Civil Engineering

INTERLINKING OF RIVERS IN INDIA

noreply@blogger.com (Civil Engineer) — Sat, 19 Jun 2010 06:59:00 +0530

The variations of the magnitude of annual rainfall in India are quite marked. It varies from an average of about 300cm in northeastern states of India to less than 15cm in its northwestern part in the semi arid and arid parts of Rajasthan and Gujarat. Also the Himalayan rivers flowing in the northern part of India are snow fed and perennial, the peninsular rivers are rain fed and seasonal. The hydrological, climatic and topographical factors cause recurrence of floods in certain parts of the country and some parts may be under scarcity of water.

The diversified distribution of dominant water demanding features such as density of population, irrigable land is the context that the interlinking of rivers for inter basin transfer of water on a national scale has been `haunting individuals and even engineers for more than a century. Linking of rivers and trans basin diversion of water is not new in our country and also other parts of the world. Diversion of river waters for cultivation of crops has been taking place from historical times. During recent times, the linking of rivers such as the Beas-sultlej link and the diversion of waters on a large scale to far off areas in rajasthan through the rajasthan canal is an excellent example. The 440 Km Narmada canal with a capacity of 40,000cusecs in the initial reach is also to supply water to some of the districts in Rajasthan. The diversion of 40,000 cusecs of Ganga waters at Farakka Barrage has also proved very useful. The present National plan for linking rivers has several components. The main ones are :

(i) Himalayan components and

(ii) Peninsular riverlinks system

The implementation of the Himalayan component depends on the co-operation of Nepal as the major tributaries of the Ganga originate in that country.

Need for Interlinking OF RIVERS: -

Somewhere people loose their lives, home, belongings due to floods or droughts. In either case people don’t have water to drink, a basic necessity for life.

Requirement of water: -

(i) Irrigation-1,060 cubic meter

(ii) Domestic water supply and live stock – 90 billion Cu-m

(iii) Agriculture – 600 billion Cu-m

(iv) Industry – 64 billion Cu-m

(v) Energy – 50 billion Cu-m

Total – 1,864 billion Cu-m

Thus the requirement of water will exceed the utilizable water resources of 1,122 billion Cu-m. The position of agriculture is no better. Today agriculture has become most unattractive job because of the floods and droughts. The Indian agriculture has been a “Gambling in monsoon”. The floods and droughts have remained permanent visitors causing havoc with Indian economy.

We witness frequent floods in some parts of the country causing havoc, devastation, damages, human suffering besides, a huge amount of public funds being spent on relief measures.

On the other hand, there is a large stretch of land vertically passing through the country as rain shadow area in the name of drought prone area, commencing from the Ramanathapuram in the south and ending up somewhere in the Ganganagar in Rajasthan traversing several districts in almost every state in south India. Many farmers died by making suicides in Karnataka due to lack of rainfall in the last five years.

Concept of interlinking of rivers: -

The concept of interlinking of rivers evolved during 1950_s.At that time, the UN promoted such projects as part of “Stability and Peace”. That was the time when big projects and technology were seen as the answer to poverty. It was also the time when many countries, after gaining independence from colonial powers wanted to express their national confidence through such major projects. The interlinking of Indian rivers proposal originated at the same time as the world became fascinated with large water infrastructure projects.

Rivers, which join, act as drainage channels and entire river system so formed drains a specified area called the basin of that system. Thus intra-basin interlinking of rivers is a natural geomorphologic process. As distinct from this, interlinking of rivers belonging to altogether different basins is not a natural process and can only take place through man made devices. Essentially inter-basin transfer of water has been done through surface irrigation projects, in which lower portion of command areas include areas in the adjoining river basin through which water is conveyed through ridge canals. Such inter-basin transfer however, is marked by the following characteristics,

(i) Transfer of water is invariably to the adjoining basins and not across basins.

(ii) Irrigation channels are generally ridge channels suitable for distribution of water as distinct from valley channel suitable for drainage of water.

(iii) Water transferred is directly used, for irrigation in this case and not brought to a river in the receiving basin and hence does not constitute interlinking of rivers, and

(iv) Transfer of water takes place through gravity flows and does not require lifting by pumps.

From the above points, it is clear that interlinking of rivers through inter-basin transfer of water is different from intra-basin linking of rivers. Interlinking of rivers that is being talked about as a national programme will have the following characteristics:

(i) It envisages linking of rivers belonging to different basins, which may or may not be adjacent.

(ii) The primary purpose of link channels will be to transfer water of a river to another river of a different basin. Any other use of a link channel will be incidental to serve the primary purpose.

(iii) Neither the lateral slope available to the tributaries linking with their parent channel nor the longitudinal slope available to ridge channels for distribution of water will be available to link channels. Hence, the link channels will almost invariably have to operate with adverse slope, making pumping or input of energy necessary. Also, the link channels, as any other channel, will be subject to seepage losses of varying magnitudes depending upon their surface and subsoil conditions.

(iv) As the objective of interlinking of rivers in the present context is to transfer water from water-surplus rivers/basins to water-deficit rivers/basins, the direction of flows in the link channel and its alignment will be determined accordingly.

NATIONAL WATER DEVELOPMENT AGENCY

National water development agent (NWDA) was set up in July, 1982 as Autonomous Society under the Societies Registration Act, 1860 under Ministry of Water Resources to carry out the water balance and other studies on a scientific and realistic basic for optimum utilisation of Water Resources of the Peninsular Rivers System for preparation of feasibility reports for interbasin transfer of water and thus to give concrete shape to Peninsular rivers Development Component of National Perspective Plan envisage by the Ministry of Water Resources. In 1990 NWDA was also entrusted with the task of Himalayan Rivers Development Component of the National Perspective.

NWDA has so far identified and investigated 16 links for peninsular rivers and 14 for the Himalayan Rivers and has carried out pre-feasibility studies with respect to about 6 of them. The Supreme court of India, in response to a public interest litigation(PIL) against inordinate delay of rivers a task for which NWDA was created about two decades ago. The president of India an avowed scientist in his own right also lent his wisdom in favour of the grand scheme. In accordance with the directive of the Supreme Court , the Task Force has been set up with a time bound mandate of taking various steps towards the implementation of the project in a period of 10 years at a tentatively estimated cost of Rs.5,60,000 crore.

The Agency is headed by the Director General Executive Officer of the Society, responsible for the proper administration of the affairs and funds of the Society and for co-ordination and general supervision of the activities of the Society. The Head Quarter for the Agency is ay New Delhi. It has two field organisations, each headed by a Cheil Engineer, 5 circles each headed by a Superintending Engineer, 15 Divisions each headed by an Executive Engineer and 8 Sub-Divisions each headed by an Assistant Executive Engineer/Assistant Engineer.

OBJECTIVES OF NWDA

(a) To promote scientific development for optimum utilisation of water resources in the country.

(b) To carry out detailed surveys and investigations of possible reservoir sited and interconnecting links in order to establish feasibility of the proposal of Peninsular Fivers Development and Himalayan Rivers Development Components forming part of National Perspective for Water Resources Development prepared by the them Ministry of Irrigation ( now Ministry of Water Resources and Central Water Commission)

(c) To carry out detailed studies about quantum of water in various Peninsular River Systems and Himalayan River Systems and which can be transferred to other basins/States after meeting reasonable needs of basin States in the foreseeable future.

(d) To prepare feasibility reports of various components of the scheme relating to Peninsular Rivers Development and Himalayan Rivers Development.

(e) To take such other actions the Society may consider necessary, incidental supplementary or conducive to the attainment of above objectives.

NATIONAL PERSPECTIVE FOR WATER RESOURCES DEVELOPMENT

The erstwhile ministry of irrigation (now ministry of water resources) and the Central Water Commission had formulated in 1980 a National Perspective Plan for optimum utilization of water resources in the country which envisages inter basin transfer of water from surplus to deficit areas. Apart from diverting water from rivers which are surplus in ultimate stage of development to deficit areas the plan enables flood moderation also. The National Perspective Plan comprises of two main components

(f) Himalayan rivers Development

(g) Peninsular rivers Development

(a) Himalayan Component

NWDA has completed the pre-feasibility studies of fourteen links in the Himalayan component too. They are namely

Manas-Sankosh-Tista Ganga link,
Jogighopa-Tista-Farakka link,
Ganga-Damodar-Subernarekha link,
Subernarekha-Mahanadi link,
Farakka-Sunderbans link,
Gandak-Ganga link,
Ghaghara -Yamuna link,
Sarda-Yamuna link,
Yamuna-Rajasthan link,
Rajasthan-Sabarmati link,
Chunar-Sone Barrage link,
Sone Dam-Southern tributaries of Ganga link,
Kosi- Ghaghara link and
Kosi-Mechi link

(b) Peninsular Components

In this component, NWDA studied in depth water balance studies of various major river basins including Mahanadi, Godavari, Krishna, Pennar, Cauvery, Vaigai, West flowing rivers of Kerala, Karnataka, north of Bombay and south of Tapi and southern tributaries of Yamuna to establish water surplus and deficit regions. These studies indicate that while Mahanadi and Godavari basins are water surplus, other basins in Peninsular India such as Krishna, Pennar, Cauvery and Vaigai are water deficit. As a next step, pre-feasibility studies for 16 probable links were carried out, of which 7 feasibility studies have also been completed by NWDA. Also, these studies suggest that it is technically possible and economically viable to transfer water from the surplus river basins to the deficit ones. Each link, in this component is briefly described here. This information is tentative and likely to change at DPR stage.

1. Mahanadi-Godavari Link

2. Inchampalli-Nagarjunasagar Link

3. Inchampalli Low Dam-Nagarjunasagar Tail Pond Link

4. Polavaram -Vijayawada Link

5. Almatti-Pennar Link

6. Srisailam-Pennar Link

7. Nagarjunasagar-Somasila Link

8. Somasila-Grand Anicut Link

9. Kattalai-Vaigai-Gundar Link

10. Pamba-Achankovil-Vaippar Link

11. Bedti-Varada Link

12. Netravati-Hemavati Link

13. Damanganga-Pinjal Link

14. Par-Tapi-Narmada Link

15. Ken-Betwa Link

16. Parbati-Kalisindh-Chambal Link

Benefits from peninsular and Himalayan rivers development components

On implementation of the proposed National Perspective Plan for inter-basin transfer of water, accrual of irrigation benefits would be to the extent of about 35 million ha (25 M-ha from surface waters and 10M-ha by increased use of ground water) which will be over and above the ultimate potential of 140 M-ha from major, medium and minor irrigation projects and generation of 34 MKW of hydropower apart from the benefits of flood control, navigation, water supply, fisheries, salinity ingress and pollution control.

Current and projected gross utilization in 2050 of surface and ground water

(Billion cubic meter)

Basin	Mean Flow	current			Projected			Percent increase
Basin	Mean Flow	Surface	Ground	Total	Surface	Ground	Total	Surface	Ground	Total
Mahanadhi	66.9	18	1.0	19.0	31.8	21.8	53.6	77	2080	182
Godavari	110.5	38	6.9	44.9	45.8	30.7	76.6	21	345	171
Krishna	69.8	47	6.3	53.3	47.8	23.0	70.9	2	265	133
Pennar	6.3	5	1.3	6.3	6.3	5.3	11.6	26	300	1821
Cauvery	21.4	18	5.8	23.8	19.9	15.1	35.0	11	160	47

CASE STUDY OF BIHAR

Bihar, a state situated in the eastern part of India, will serve and apt case to illustrate various issues and aspects related to interlinking of rivers. In the envisaged national scheme of interlinking of rivers, Bihar occurs significantly, probably as a water surplus region.

The present day Bihar, after a separate state of Jharkand, can be considered as comprising two distinct hydrological regions, North Bihar lying north of the river Ganga up to its border with Nepal and South Bihar lying south of Ganga adjoining Jharkand. While most of Bihar is part of the Ganga basin, north Bihar is drained by rivers originating in the Himalayas and Nepal, and south Bihar is drained by rivers originating in the Vindhyan, Chhotanagpur and Rajmahal hills. All these rivrs join Ganga at various confluence points lying mostly in Bihar.

The fact that rivers of north Bihar cause recurrent floods, ie; they carry more water than they can contain within their banks and hence it is concluded that if this excess flow is transferred to a water deficit river/basin, it will not only provide valuable water to serve its needs but would also solve the problem of floods in north Bihar. For this, each component of the view is dealt with separately as follows.

RECURRENCE OF FLOODS AS CONCLUSIVE EVIDENCE OF SURPLUS

In the case of north Bihar, recurrent sccurences of floods are caused by a combination of the following five factors,

(i) Hydrometeorological

The catchment areas of north Bihar rivers receive almost 85% of their annual precipitation during 4 months of the south-west monsoons during June-September, mostly concentrated during July and August. The annual precipitation varies from 130 cm in the North Bihar plains up to 300 cm on the southward slopes of the Himalayan part of the catchments in Nepal.

(ii) Hydrological

On an average, more than 60% (85% in the case of Kosi and 76% in the case of Gandak) of the aggregate catchments areas of north Bihar Rivers lie in high precipitation region outside north Bihar, mostly in Nepal.

(iii) Topographical

Catchments of north Bihar rivers undergo a very large and sharp change in gradients from very steep in the mountainous (Mt. Everest lies in these catchments) to steep in the sub-mountainous parts to extremely mild in the north Bihar plains through a relatively short stretch of 300 Km.

(iv) Hydraulic

When high flows resulting from run-off transformation of seasonally concentrated precipitation in higher precipitation upper catchments areas travel from steep gradients and encounter mild gradients downstream, they exceed the conveyance capacities of rivers in their lower reaches. So they spill over the banks and inundate the flood plains, using them as temporary dynamic storage.

(v) Demographic

as the inundated flood plains support habitation, agriculture and other activities of a high-density population, floods cause recurrent disruption, damages and devastations on a large, attractin national attention. Recurrent floods in north Bihar constitute a case of ill management of water resources rather than being an indication of water being in surplus on an annual and basin wide scale. This is also linked by other facts and situations as mentioned below,

(a) It is common experience that crops damaged by floods at one time suffer from agricultural drought subsequently. In Bihar, it is estimated that agricultural droughts cause 25% less in crop yields.

(b) About 30% of cultivable land in north Bihar is presently under irrigation, while 90% of the cultivable land is irrigable. When this high potential irrigation is provided, agricultural water demand will rise considerably.

As per the “Report of second Bihar state irrigation” commission(1994) , irrigation water demands will fall short of availability of water in the state to meet food grain requirements of the rising population by the year 2025.

(c) When India and Nepal will agree to co-operate in developing their shared water resources comprehensively, not only will north Bihar rivers be free from recurring floods, but other beneficial uses of water- consumptive as well as non-consumptive such as for irrigation, hydro-power generation, water transport, industrial as well as municipal uses and aquaculture will also be secured for immense mutual benefits. In that case, the perception of north Bihar rivers being water surplus will undergo a fundamental and conceptual change.

ENVIRONMENTAL, ECOLOGICAL AND HUMAN IMPACT

As interlinking of rivers is achieved by a combination of engineering measures such as dams, barrages, cross drainage structures and link channels, environmental and ecological impacts as well as displacement of people resulting form each of them will be the consequences of interlinking.

The link channels of interlinking system will be different from natural or other man made channels in the following ways along with their associated consequences. The purpose of a link channel is conveyance and transfer of water, as distinct from a natural channel, which is for drainage or irrigation channel which is for distribution of water or a navigation channel where basically depths are maintained for plying of boats. Link channels will mostly be in filling to avoid excessive lift, will have to cross natural drainage channels and may pass through forested or inhabited areas. These channels will generally carry high discharges requiring large cross sections, and hence these factors will lead to the following consequences.

(1) Unless the link channels are lined, which will be a cost-prohibitive proposition, will cause heavy seepage which will not only constitute loss of water under transfer but may also create water logging conditions in certain areas.

(2) They are likely to cause substantial displacement of people giving rise to problems of resettlement and rehabilitation. As the people to be displaced will be far from being beneficiaries, there is bound to be resistance on their part.

(3) As these long link channels may pass through dense forest and habitats of wildlife, their ecological consequences may be serious and substantive.

(4) Import of vast amount of water in arid or semi-arid areas may adversely affect their dry land ecology.

EXISTING INTER BASIN TRANSFER PROJECTS

The periyar Project, Parambikulam Aliyar Projet, Kurnool-Cudappah Canal and the Telugu Ganga Project in the south and inter sub-basin transfers in the Indus basin and Rajasthan canal project in the north are good examples of inter basin water transfers executed in India in 19^th and 20^th centuries.

The Periyar project

A masonry gravity dam 47.28m high has been constructed across a gorge on west flowing Periyar river. A1,740m long tunnel with a discharging capacity of 40.75m³/s has been driven across the mountain barrier to convey the waters eastwards to Vaigai basin. The project was commissioned in 1895 and provided irrigation to 57,923ha initially, which has since been extended to 81,069ha. There is also a power station of 140 MW capacity.

Rajasthan canal project

The project diverts water from the Himalayas to the deserts of Rajasthan. The projet comprises of a huge multipurpose project constructed across the Beas river at Pong, a barrage at Harike and a grand canal system.

ABROAD

(i) In United States, the California’s state water project, first phase of which was completed in 1973, provides for the diversion of 4 cubic Km of flow from better watered northern California to the drier central and southern parts of the state. The conveyance system comprises of 715 Km long California aquaducts a complec system of lined and unlined canals, pumping stations, siphons and tunnels. The lift involved is nearly 1,000m.

(ii) Inter basin transfer projects have also been planned and implemented in China and former USSR. A notable scheme executed in the USSR is Irtysh Karaganda scheme in the central Kazakistan. The link canal is about 450 Km long with a maximum capacity of 75 cumecs. Lift involved is 14 to 22 m. other proposals include partial redistribution of water resources of northern rivers and lakes of European part to the Caspian sea basin involving 2 M.ha-m of water.

(iii) In china recently completed inter basin transfer include Biliuha-Daliah inter basin water supply system, trans basin transfer of Luhana river to Tiajian river and Tengshan. Diversion of yellow river surpluses and south to north transfer project.

Promises	Pitfalls
Transfer 173 billion cubic metres of water to water-stressed regions	More inter state water disputes; Diplomatic row with Bangladesh &Nepal
Building 11000km of canal network	Increased incidence of water logging and submergence of 79,292 ha of forests.
Generate 34000 MW of power	Rising funds a constraint; cost-overturn to make the project prohibitively costly.
Boost GDP growth by 4%	4.5 lakh people to be displaced.

The foreign schemes give confidence for planning inter-basin water transfer schemes in India. At the same time, lessons have to be learnt from their actual performance, economic viability and environmental suitability.

The envisaged benefits to water-deficit regions of the country through interlinking of rivers and also solution for problems such as flood as seen from case study of Bihar should be assessed and analysed in terms of economic, environmental and ecological as well as social cost involved and finding options and alternatives in the context.

The conceptual, technological and economic aspects of interlinking need comprehensive examination and analysis.

APPLICATION OF “FUZZY CONCEPTS” IN CIVIL ENGINEERING

noreply@blogger.com (Civil Engineer) — Sat, 19 Jun 2010 06:50:00 +0530

It has increasingly been recognized that our society is undergoing a significant transformation, usually described as a transition from an “Industrial to an Information Society”.

In this span of transformation, one way of simplifying a very complex system perhaps the most significant one – is to allow some degree of uncertainty in its description. It is entails an appropriate aggregation or summary of the various entities within the system. Statement obtained from this simplified system are less precise, but their relevance to the original system is fully maintained. That information loss that is necessary for reducing the complexity of the system to a manageable level is expressed in UNCERTAINTY. The concept of Uncertainty is thus connected with both complexity of information 1

Thus, complexity and information are closely interrelated. During this course of time, the realization of Uncertainty, vagueness and ambiguity in the world has led to the concept of fuzziness.

Uncertainty – it’s the state of being uncertain, something that you cannot be sure

That. Where as, our statistics & probabilistic approaches deal with

uncertainty.

Vagueness – not clear in person’s mind.

Ambiguity – it’s the state of having more than one possible meaning.

Hence, due to these constraints; the idea of fuzzy sets was born in 1964, and in 1965 Lofti A. Jadeh a well respected professor in the department of Electrical Engineering & computer science at university of California presented a paper on FUZZY SETS 2.

This made to the development of new mathematical formulation called the FUZZY CONCEPTS by himself (Jadeh) & and his followers.

In the last 3 decades, significant progress has been made in the development of Fuzzy sets and Fuzzy logic theory in Engineering, Natural and socio-economic science.

The successful applications of fuzzy sets and fuzzy logic can be attributed to the fact that the fuzzy theory reflects the true situation of the real world, where human thinking is dominated by approximate reasoning logic.

* For example, during the design stage, decision making is mainly based on conceptual understanding. Unfortunately, such information is usually vaguely defined by the experts. Therefore, consideration of imprecise and vague information becomes an important issue in an automated design environment.

2.0. Application to Civil Engineering tiled

Engineering field acts as platform for the application of fuzzy concepts. We know that Civil Engineering field is fundamentally different from other disciplines. It means that the theories never fully satisfy the problem considered. This is because, the civil engineering project is complex and usually large in nature: hence, there will be almost no chance to test the prototype compared to other disciplines. As result, there is uncertainty in application of theoretical solutions. More over, our engineering problems are constraint satisfaction problems.

Example: when we trying to determine the best frame design for a building, one may be constrained by design codes as well as by the design specifications such as functional, architectural and structural behavior requirements. Once these constraints are satisfied the remaining problem may be to find and design that requires the least construction material. These, constraints mush be strictly satisfied without disregarding them.

There by, these complexities, uncertainties and vagueness in decision making in real structure provide the main motivation for the use of fuzzy concepts. Its proven by the experts that the fuzzy concept is a useful tool and can be effectively applied for the problems in civil engineering in order to arrive at the optimal solution.

During the last decade there has been a growing interest in the application of these concepts to engineering problems. Fuzzy concepts provide an easy way of dealing with complex problems, because it can be built with fuzzy models containing vagueness and impreciseness in knowledge representation. Hence, it is suited for applications where the ability to model real world design problem in precise mathematical form is difficult.

Also by integrating Fuzzy concepts with Genetic Algorithms (GA) or Genetic Programming (GP) and Neural Networks (NN), the complex problems can be more efficiently and effectively solved in order to arrive at optimal soln.

So fat, these concepts are effectively used in;

· Structural analysis and Design

- for structural optimization and optimum Design of structures [ Y.Yang & C.K. soh (2000)].

- Computation Morphogenesis of Deserete structures [ H. Kawamura et al. (2004)].

Construction field

- for management problems like construction scheduling of the project [ S.S. Leu et al. (1999)]

- for planning of life cycle of project problems like selection of best construction equipment.*

[V.S.S. Kumar et al. (2004)]

· The field of Hydrology & Water Resource engineering.

- for forecasting rainfall, rainfall runoff, river stage, etc.

[Chandramouli et al. (2001)]

- Hydrologic flow routing [Paresh Deka et. al. (2005)]

· Traffic engineering

- for automatic control of traffic signals based on fuzzy stochastic model [George J. Klir et al.]

· Reliability of structures

- for damage assessment in structures [W. Chiang et al. (2000)]

· Metal structures

- for predicting fatigue & Creep characteristics [J. Harris (2001)]

Fuzzy concepts thrown its wide variety of application for the field of civil engineering. Hence, we the engineers should explore it for its potential application for the problems we face in this engineering world.

3.0. FUZZY CONCEPTS

Fuzzy concepts is mainly of Fuzzy set and Fuzzy logic theories. Before, we get into the discussions of these theories let us discuss classical or crisp sets.

3.1 Classical or crisp sets

A classical set is a collection of objects in a given domain. In which object either belongs to the set or does not belong to the set. Therefore, there is a sharp boundary between members of the set and those not in the set.

We can say, classical sets divide the world into yes & no, true & false and white & black.

i.e, membership in a classical set is a yes & no or true & false or white & black concept.

The classical set can be represented as:

Membership function is;

Where:

C- an arbitrary crisp set

X – an element in the set

U – membership function

Limitation:

It has sharp boundary between members of the set and those not in the set.

3.11 Classical set operations:

There are three basic set operations

Where:

U is a universe discourse

A & B are sets inU.

There three basic operations have several fundamental properties interms of

Laws. They are:

1. Commulative law

2. Associative law

3. distributive law

4. Law of Double complementation

5. Demorgan’s law

6. Law of Excluded middle

7. Law of Contradiction

8. Law of Tautology

9. Law of Absorption

3.2 Fuzzy set theory

Fuzzy set theory generalizes classical set theory.

The best way to introduce fuzzy sets sis to start with a limitation of classical sets. Fuzzy set theory directly addressess this limitation by allowing membership in a set to be a “matter of degree”. The degree of membership in a set is expressed by a number between 0 & 1 ‘0’ means complete Exclusion from the set and ‘1’ means absolute INCKUSION in the set. Such a function which maps object in a domain of concern to their membership value in the set is called as “membership function” (u).

The membership represents a certain degree of belonging of the object in the fuzzy set. The transition from belong to not belonging is gradual, which gives one some means of handling vagueness. Fuzzy sets thus overcome a major weakness of crisp sets.

i.e, Fuzzy sets do not have an arbitrarily established boundary to separate the members from nonmembers. Thus in a fuzzy set membership function can be represented as:

The discussion on classical set and fuzzy set can be represented graphically:

3.2.1. Membership function

What is important about membership function is that it provides gradual transition from regions completely outside a set to regions completely in the set.

There are, numerous types of membership functions, but the most commonly used in practice are triangles, trapezoioh, bell curves, Gaussian and sigmoidal functions.

In which triangles and trapezoid membership functions are more frequently used.

3.2.2. Representation of fuzzy sets

Fuzzy sets can be represented in two ways:

1. by enumerating membership values of those elements in the set completely or partially.

2. by defining the membership function mathematically.

Generally speaking, a fuzzy set ‘A’ be defined through enumeration using expression.

Similarly. When U (universe of discourse) is a set of interval of real members, then:

3.2.3. Fuzzy set operations.

The fuzzy set theory is formulated in terms of the following specific operators.

1. A common fuzzy conjunction (AND) operation is the minimum operator.

Example: Figure shows the result of using min. to form the intersection of two fuzzy sets is:

2. A common fuzzy disjunction (OR) operation is the max. Operator.

Example: Figure shows the result of using max. to form the union of two fuzzy sets as;

3. A complement of fuzzy set A defined by the difference between one and the membership degree in A.

Example: Figure shows Fuzzy set medium.

It should be noted that the range of membership degree is restricted to the set {0, 1}.

3.2.4. A paradox in fuzzy set theory

It doesnot mean that fuzzy set theory should hold all the laws of classical sets.

i.e, failing of the law of excluded middle and the law f contradiction.

We know that fuzzy concept generalizes the black & white concept, by varying the membership to allow “gray areas”, it has to violate two fundamental laws of set theory.

i.e, Law of excluded middle

& the law of contradiction

In other words, it is possible for an element to partially belong to both fuzzy set and sets complement.

Example: Mr. X is a person belongs to the set of bald people to degree 0.2.

i.e, μ bald (X) = 0.2

Based on the definition of complement operator, Mr. X belongs to the complement of bald people to degree 0.8.

i.e, μbald (X) = 0.8

The person partially belongs to the set of bald people as well as the set of people who are not bald.

In fuzzy theory any element partially belonging to fuzzy set, is also partially member of its complement.

Hence, we can say that law of excluded middle & law of contradiction are not axioms of fuzzy theory.

3.2.5. Hedges:

A hedge is a modifier to a fuzzy set. It modifies the meaning of the original set to create a compound fuzzy set.

Very & more or less are two commonly used hedges. Their definitions are listed below.

Figure illustrates their application to the concept of high temperature.

“Very” has the effect of narrowing the membership function.

“More or less” widens the membership function.

This is intuitively appealing because the criteria for “Very high” should be more stringent that those for “thigh”, while the criteria for “more or less high” should be relaxed.

Hence, we can express

In principle, a hedge can be applied to any fuzzy set. In practice, however it is used only when the compound terms is meaningful. For instance, very medium temperature, very excellent.

3.2.6. General aggregation operations:

Aggregation operations on fuzzy sets are operations by which several fuzzy sets are combined to produce a singe set.

In general, any aggregation operation is defined by a function

h = {0, 1}n – [0,1]

when applied to ‘n’ fuzzy sets {Al, A2, ------An} defined on ‘U’, ‘h’ produces an aggregate fuzzy set ‘A’ by operating on the membership grades of each χ € U in the aggregated sets.

Thus,

In order to quality as an aggregation function “h” must satisfy at least the following two axiomatic requirements, which express the essence of the notion of the aggregation.

Axiom 1: If h = {0, 0, -------0} = 0

and h = { 1, 1, ------1} = 1 as boundary conditions.

Axiom 2. For any pair,

i.e, ‘h’ is monotonic nondecreasing in all its arguments the other two additional axioms which we commonly use are:

Axiom 3: ‘h’ is a continuous function.

Axiom 4: ‘h’ is a symmetric function in all its arguments.

i.e,

Fuzzy unions and intersections can be easily qualify as aggregation operations on fuzzy sets.

Note: In application to problems various types of aggregation procedures can be used to in corporate exports judgments.

3.2.7 Properties of fuzzy sets

Convex fuzzy set

The height of a fuzzy set is the largest membership grade affined by any element in that set. A fuzzy set is called normalized when at least one of its elements attains the maximum possible membership grade. If membership grades range in the closed interval between 0 and ‘1’, then at least one element must have a membership grade of ‘1’ for the fuzzy set to be considered normalized such a normalized fuzzy set to be considered as a convex fuzzy set if and only if:

If the above statement is violated, then such a fuzzy set is a nonconvex fuzzy set.

- Cut of a Fuzzy set:

An - cut of a fuzzy set A is a crisp set A that contains all the elements of the universal set U that have a membership grade in A greater that or equal to the specified value of . this definition can be written as:

The value ‘ ‘ can be chosen arbittrarity but is often designated at the values of the membership grades appearing in the fuzzy set under consideration.

Example: consider the concept “moderately approved” regarding the public opinion of a presidential candidate. The universe of discourse is the % of those people supporting the candidate in a poll

Let U = [ 0%, 10%, 20%......... 100%]

The membership function of a fuzzy set

Cardinality of fuzzy set:

The cardinality of a set is the total number of elements in the set. Since, an element can partiality belong to a fuzzy set, a natural generalization of the classical notion of cardinality is to weigh each element by its membership degree, which gives us the following formula for calculating the cardinality of a fuzzy set:

The cardinality of fuzzy sets is useful for answering questions. Therefore, it plays on important role in fuzzy databases and information systems.

3.3 Linguistic variables:

A linguistic variable is defined as a variable whose values are in words, phrases or sentences in a given language.

Having introduced the fundamental concept of a fuzzy set, it is natural to see how it can be used. Like a conventional set, conventional set, a fuzzy set can be used to describe the value of a variable.

For example, if the variable is linguistic one say “site conditions” which can take the values of excellent, fair, poor, etc. The fuformation expressed in words or phrases in this example has a value but it is not clearly defined. These values scan be made susceptible to meaningful classifications.

Jadeh considered these values as fuzzy sets.

i.e, U = {site conditions}

This universal set consists the sub sets as

U = {excellent, fair, poor}

In which membership values may be given for the subsets considering their ranges.

In the manner, fuzzy sets can well be considered for quantifying qualitative factors.

If the Degree of belief in a fuzzy set is say getting narrowed, then the linguistic variables can be described as say very excellent, very fair, very poor, etc.

This can be represented graphically as;

Instead of enumerating all these different linguistic descriptions, they can be generated from a core set of linguistic terms using “modifiers”. In fuzzy theory we call these modifiers as HEDGES as discussed earlier.

NOTE: The interpretation of fuzzy linguistic terms has been clearly given by Jadh [Fuzzy sets and applications (1984)]

3.4. Fuzzy Logic

The foundation of fuzzy logic is mathematically the fuzzy set theory. This logical technique is based on four basic concepts.

1). Fuzzy sets

2). Linguistic variables

3) Possibility distribution

4) Fuzzy if – then rules.

· Fuzzy sets – sets with smooth boundaries

· Linguistic variables – variables whose value are both qualitatively and quantitatively described by a fuzzy set.

· Possibility distribution – constraints on the value of a linguistic variable imposed by assigning it a fuzzy set.

· Fuzzy if – then – a knowledge representation scheme for describing a functional mapping or a logic formula that generalizes an implication in two valued logic.

Frame work of these concepts results in a “Fuzzy logic controller” (FLC).

3.4.1 Fuzzy logic controller [FLC].

A fuzzy logic controller (FLC) is a rule based system that incorporates the flexibility of human decision making by means of the use of fuzzy set theory. The fuzzy rules of FLC incorporate fuzzy linguistic terms described by membership functions. These functions are intended to represent human experts conception of the linguistic terms, thus giving an approximation of the confidence with which precise numeric value is described by a linguistic label.

Fuzzy rules take the form. If (conditions or inteceden) and THEN (actions or consequent). Where conditions ad actions are linguistic labels applied to input and output variables, respectively.

A set of such fuzzy rules conciliates the Fuzzy rule as of FLC. The system uses this rule base to produce precise output values according to the input values.

Control process is divided in to three stages.

· FUZZIFICATION: to calculate the Fuzzy input (i.e, to evaluate the input variable w.r. to to corresponding linguistic terms I the condition side).

· FUZZY INFERENCE: to calculate the Fuzzy output (i.e, to evaluate the activation strength of every rule base and combine their action sides.

· DEFUZZIFICATION: to calculate the actual output (i.e, to correct the Fuzzy output into precise numerical value).

· So, this is just an outlook discussion of Fuzzy concepts, if yougo n depth, explore it & understanding; it will help in applying these concepts to a complex problem, so that the problem can be tuned to meet all constraints or in over coming all the uncertainties, ambiguity & vagueness .

3.5. Considering the CASE STUDY : A Fuzzy logic approach to selection of Cranes.

3.5.1 INTRODUCTION

Selection of a crane on construction projects is a central element in the planning phase of the life cycle of the project. An appropriately selected crane is the life blood of many multistory construction projects and contributes largely to the efficiency, timeliness, and profitability of the project. An error in selection can lead to large and unnecessary expenses arising from operational inadequacy or Failure, and can produce an unsafe working environment. Decision to select a particular crane depends on

many input parameters such as site conditions, economy, safety and weather conditions and their variability. Many of these parameters are qualitative, and subjective judgments implicit in these terms cannot be directly incorporated into the classical decision making process.

Therefore, it is important to find some way of incorporating an expert’s knowledge on these qualitative Factors into the selection process. One way of achieving this, by the development of fuzzy logic to decision making process. In this, expert’s opinion interns of membership values of fuzzy sets are aggregated by modified pessimistic aggregation procedure and final selection of a crane is achieved by max-min criteria.

The objective of this paper is to provide a methodology to select the most appropriate crane using a fuzzy logic approach by considering the viewpoints of the experts in relevant fields.

3.5.2. Classification of cranes.

A crane is defined as a mechanism for lifting and lowering loads with a hoisting mechanism. On many construction sites a crane is needed to lift small to medium loads such as concrete skips, reinforcement, and form work. As the lifting needs of the construction industry have increased and diversified, a large number of general and special purpose cranes have been designed and manufactured.

Mobile cranes:

A mobile crane is crane capable of movement under its own power without being restricted to predetermined travel. Mobility is provided by mounting or integrating the crane with trucks by providing crawlers. Truck-mounted cranes have the advantage of being able to move under their own power to the construction site. Additionally, mobile cranes can move about the site, and are often been able to do the work of several stationary units.

Tower Cranes:

The tower crane is a crane with a fixed vertical most and equipped with a winch for hoisting and lowering loads. Tower cranes are designed for situations which require operation in congested areas. Congestion may arise from the nature of the site or from the nature of the construction project. There is no limitation to the height of a high rise building that can be constructed with a tower crane. The very high line speeds, up to 304.8m/min, available with some models yield good production rates at any height. They provide a considerable horizontal working radius, yet require a small work space on the ground. Some machines can also operate in winds of upto 72.4km/hr, which is far above mobile crane wind limits.

Derrick Cranes:

A derrick is a device for raising, lowering, and moving loads laterally. The simplest form of the derrick is called a Chicago boom and is usually installed by being mounted to building during construction. This derrick arrangement becomes a guy derrick when it is mounted to a mast and a stiff leg derrick when it is fixed to a frame.

An appropriately selected crane contributes, efficiency, timeliness, and profitability to the project. This is achieved using fuzzy logic approach.

3.6. Translation of qualitative factors into fuzzy sets:

The qualitative factors that are commonly used in the selection of cranes need to be translated into mathematical measures. For example, high temperature, inadequate external access, and poor design co-ordination can be considered as qualitative factors. The resulting quantitative indices for these variables are known as fuzzy variables.

Let U be a universe of linguistic variable set of element’x’s, and A be a subset of U. that is, variability of a linguistic variable. Each element, ‘x’, is associated with a membership value ma (x) , to the subset ‘A’, in which ma (x) is the grade of membership if x in A, and us a real number.

Therefore, variability of qualitative factor

A= (x, ma(x) ), xEA&AEU.

For example, the linguistic variable “Weather conditions” is interpreted , using the following membership function. The “universal set” is “weather conditions” as a variable. The linguistic quantification for this variable can be expressed by fuzzy sets. Dividing the range into increments of 0.1, the following fuzzy set ‘poor’ can be assigned for the variable ‘poor weather conditions

ANAEROBIC DIGESTION

noreply@blogger.com (Civil Engineer) — Sat, 19 Jun 2010 06:42:00 +0530

Anaerobic digestion promotes the bacterial decomposition of the volatile solids in animal wastes to biogas, thereby reducing lagoon loading rates and odour. The primary component of an anaerobic digestion system is the anaerobic digester, a waste reactor containing bacteria that digest the organic matter in waste under controlled conditions to produce biogas.

Anaerobic digestion is widely applied in the treatment of high strength municipal sludges and industrial wastes, where the BOD is more than 1500mg/lt. It is the oldest processes used for the stabilization of solids and bio-solids. This seminar discusses about the anaerobic digestion processes, design and some applications, in detail.

Organic waste has the potential to cause significant pollution through atmospheric methane, polluted groundwater and the spread of diseases. Anaerobic digestion - a technology that has traditionally been viewed as simply 'energy-from-waste' technique - can provide a range of benefits in addition to the valuable renewable energy from biogas.

Anaerobic digestion is a technology that is generally perceived of as a waste treatment technology. However, in its broadest sense, it is a natural process harnessed by mankind. Anaerobic digestion (AD) is a biological process in which biodegradable organic matters are broken-down by bacteria into biogas, which consists of methane (CH₄), carbon dioxide (CO₂), and traces of other gases. Absence of Oxygen is the primary requirement of AD to occur. Anaerobic digestion provides an effective method for turning residues from livestock farming and food processing industries into:

· Biogas (rich in methane), which can be used to generate heat and/or electricity

· Fibre which can be used as a nutrient-rich soil conditioner, and

· Liquor, which can be used as liquid fertilizer.

Anaerobic processes could either occur naturally or in a controlled environment such as a biogas plant. Organic wastes such as livestock manure and various types of bacteria are put in an airtight container called digester so that the process could occur. Depending on the waste organic matter and the system design, biogas is typically 55% to 75% pure methane. State-of-the-art systems report producing biogas that is more than 95% pure methane.

SOURCES OF WASTE ORGANIC MATTERS

Food Waste: Fruits, vegetables, dairy products, bakery waste, meat, pre/post consumer food wastes (liquid or solid), processed and frozen foods.

Yard Waste: Leaves, grass, plant material, etc.

Fibre Waste: Paper products, polycoat, boxboard, towels, napkins, tissues, waxed plates/cups, books, directories, magazines, newsprint, disposable diapers, feminine hygiene products, incontinence Pads etc.

Miscellaneous Waste: Pet wastes, hair, vacuum cleaner bags, sawdust, etc.

Industrial, Commercial & Institutional Waste: Agricultural waste (food, straw, chaff , manures), organic sludges and slurries (label and brewery pulps, filtration etc), glycol and other alcohols, slaughterhouse slurries, food processing residues. Industrial waste and wastewater usually come from food/beverage industry, starch industry, sugar industry, paper processing, slaughterhouse (gastrointestinal wastes), chemical industry, pharmaceutical industry, dairies, cosmetic industry, fish oil and fish processing residues.

PRINCIPLE OF THE ANAEROBIC DIGESTION:

The Digestion Process

Anaerobic decomposition is a complex process. It occurs in three basic stages as the result of the activity of a variety of microorganisms. Initially, a group of microorganisms converts organic material to a form that a second group of organisms utilizes to form organic acids. Methane-producing anaerobic bacteria utilize these acids and complete the decomposition process.

The anaerobic digestion process can be carried out in quite different conditions. All of these conditions have specific influences on the biogas production. Additionally, from a technological viewpoint, the biological process can also be carried out in more than one reactor, which has some, mainly economical, implications.

"Dry" digestion and "wet" digestion

In the digestion processes, water is an important parameter. Water is needed for life in general and for digestion bacteria too. It is an important medium for the transport of nutrients, for products and it is a very good reaction medium for digestion.

Digestion is practiced in two different ranges of water content: dry digestion, with a typical dry solids content of 25-30% and wet digestion, with a dry solids content of less than 15%. These ranges have technological and economic reasons: higher solid contents leads to smaller reactors, lower solid contents (more water) lead to much better mixing possibilities but to a higher energy input (more water to be heated) and a bigger reactor.

Natural wastes from plants (like greenhouse residues), have an estimated dry solids content of 25%. This dry solids content opens the possibility to perform the digestion without addition of water.

Batch processes and continuous processes

In process technology the two main types of process (models) are used, the batch process and the continuous process. In the batch process the substrate is put in the reactor at the beginning of the degradation period after which the reactor is closed for the entire period without adding additional substrate. In the continuous process, the reactor is filled continuously with fresh material and also emptied continuously.

As explained before, digestion consists of several consecutive steps. In a batch reactor, all these reaction steps occur more or less after each other. The production of biogas (end product) is non-continuous: at the beginning only fresh material is available and the biogas production will be low. Halfway through the degradation period the production rate will be highest and at the end, when only the less easily digestible material is left, production rate will drop again.

In a continuous process, fresh substrate is added continuously, and therefore all reactions will occur at a fairly constant rate resulting in a fairly constant biogas production rate. Several mix forms of these two models are developed in process technology including the so-called plug-flow reactor and the sequencing batch-reactor all of which try to combine the advantages of the two extremes.

Environmental Factors affecting the digestion

The environmental factors affecting anaerobic digestion include solid retention time, nutrients, pH, temperature, Volatile fatty acids and toxic materials.

Mixing of the digesting material: Pre-sizing and mixing of the feed material for a uniform consistency allows the bacteria to work more quickly. Occasional mixing or agitation of the digesting material can aid the digestion process.

Retention time: Retention time is the time needed to achieve the complete degradation of the organic matter. The retention time varies with process parameters, such as process temperature and waste composition. The retention time for waste treated in a mesophilic digester ranges from 15 to 30 days and 12 to 14 days for thermophilic digester.

The three reactions (hydrolysis, fermentation, and methanogenesis) are directly related to solid retention time (SRT= mass of solids in the reactor / mass of solids removed daily). An increase or decrease in SRT results in an increase or decrease in the extent of each reaction. There is a minimum SRT for each reaction. If the SRT is less than the minimum SRT, bacteria cannot grow rapidly enough and the digestion process will fain eventually.

Nutrients: Nutrients must be present in sufficient quantities to ensure efficient digestion. The nutrients required in highest concentration are nitrogen and phosphorous. Nitrogen is used in synthesis of proteins, enzymes. Phosphorous is required to synthesis energy storage compounds ATP (adenosine tri-phosphate) RNA and DNA. Other nutrients required are Iron, Nickle, Cobalt, Sulphur and Calcium.

Temperature: Anaerobic digestion can occur under two main temperature ranges:

Mesophilic conditions, between 20-45ºC, usually 35ºC.

Thermophilic conditions, between 50-65ºC, usually 55ºC. digestion:

Thermophlic is much faster than mesophilic. Advantages cited for thermophilic include increased solids destruction capability, improved dewatering, and increased bacterial destruction. Disadvantages of thermophilic are higher energy requirements for heating, poorer quality supernatant containing larger quantities of dissolved solids, odours and less process stability. Thermophilic systems offer higher methane production, faster throughput, better pathogen and virus ‘kill’, but require more expensive technology, greater energy input and a higher degree of operation and monitoring. However, the process is highly sensitive to disturbances such as changes in the feed materials and temperature.

To optimize the digestion process, the digester must be kept at a consistent temperature, as rapid changes will upset bacterial activity. The sterilization of the waste is also linked with the temperature. The higher it is the more effective it is in eliminating pathogens, viruses and seeds.

pH: The optimal pH values for the acidogenesis and methanogenesis stages are different. During acidogenesis, acetic, lactic and propionic acids are formed and, thus the pH falls. Low pH can inhibit acidogenesis and pH below 6.4 can be toxic for methane-forming bacteria. The optimal pH range for all is between 6.4 and 7.3.

Volatile fatty acids: Anaerobic reactor instability is generally manifested by a marked and rapid increase in volatile fatty acids concentration. Concentration of acetic acid of 1000mg/l has no inhibitory effect on methanogens. However, at low concentration 100mg/l of the propionic acid are inhibitory to anaerobic digestion.

Carbon to Nitrogen ratio (C:N): The relationship between amount of carbon and nitrogen present in organic materials is represented by the C: N ratio. Optimum C: N ratios in anaerobic digesters are between 20 and 30. A high C: N ratio is an indication of a rapid consumption of nitrogen by the methanogens and results in a lower gas production. On the other hand, a lower C: N ratio causes ammonia accumulation and pH values exceeding 8.5, which is toxic to methanogenic bacteria. Optimum C: N ratio of the organic matter materials can be achieved by mixing waste of low and high C:N ratio, such as organic solid waste mixed with sewage or animal manure.

Toxicity: The natural of toxicity in biological waste treatment is often misunderstood especially to anaerobic digestion. Whether a substance is toxic to a biological system is a matter of the nature of substance concentration and acclimation. Many substances will stimulate the reactions in low concentrations. However, as concentration increases the effect becomes inhibitory.

It is often presumed that methane-producing bacteria are dead once gas production goes to zero. This is not necessarily true. It was found that maintenance of proper sludge retention time (SRT) is extremely important in allowing for acclimation to toxicants tend to alter their growth kinetics by increasing bacterial generation time. If SRT is too low, dormant methane bacteria will be washed out of the system prior to acclimation or metabolism of the toxicants.

Chlorinated hydrocarbons are extremely toxic to anaerobic digestion. Ethyl benzene concentration can reduce the activity by 25% to 60%. The solvent ethylene dichloride is found to severely inhibit methane fermentation. Also antibiotics in livestock feed have been known to kill the anaerobic bacteria in digesters. So the Complete digestion, and retention times, depends on all of the above factors.

How does AD work?

The digestion process takes place in a warmed, sealed airless container (the digester), which creates the ideal conditions for the bacteria to ferment the organic matter in the absence of oxygen. The digestion tank needs to be warmed and mixed thoroughly to create the ideal conditions for the bacteria to convert organic matter into biogas.

Anaerobic digestion is a complex process, which consists of three stages of

1) hydrolysis, 2) Acidogenesis, and 3) Methanogenesis.

1) Hydrolysis: During hydrolysis insoluble complex organic matter such as cellulose is decomposed into simple soluble organic molecules such as fatty acids, amino acids and sugar, using water to split the chemical bonds between the substances. Then, it can be utlised by the bacteria, which is achieved by extracellular, hydrolytic enzymes produced and excreted by the bacterial population for this specific purpose. Chemicals can be added during this stage in order to decrease the digestion time and provide a higher methane yield.

2) Acidogenesis: In this stage, acetogenic bacteria degrade amino acids, sugars, and some fatty acids further into simple organic acids, carbon di oxide and hydrogen. The principle acids produced are acetic acid, butyric acid, propionic acid and ethanol.

3) Methanogenesis: Methanogenesis is carried out by a group of organisms known as methanogens. Two groups of methanogenic organisms are involved in methane production. One group, termed aceticlastic methanogens, split acetate into methane and carbon dioxide. The second group, termed hydrogen-utilizing methanogens, the acetic acid will be converted to methane. Waste stabilization occurs during the methanogenic phase of conversion of the acetic acid into methane, which is insoluble in water. So approximately 72% of the methane formed in the anaerobic digestion of wasterwater comes from acetate cleavage.

CH₃COOH -------- CH₄ + CO₂

The remaining 28% results from reduction of carbon dioxide using hydrogen as energy source by CO₂ – reducing methanogens.

C0₂ ± H₂ ----- CH₄ + H₂O

Biogas produced in anaerobic digestion is primarily composed of methane (CH₄) and carbon dioxide (CO₂), with smaller amounts of hydrogen sulphide (H₂S) and ammonia (NH₃). Trace amounts of hydrogen (H₂), nitrogen (N₂), carbon monoxide (CO), saturated carbohydrates and oxygen (O₂) are occasionally present in the biogas. The composition of biogas is different from the one of natural biogas but it is quite similar to landfill gas.

Types of Anaerobic Digesters

There are three basic digesters. All of them can trap methane and reduce fecal coliform bacteria, but they differ in cost, climate suitability, and the concentration of manure solids they can digest.

A covered lagoon digester , as the name suggests, consists of a manure storage lagoon with an impermeable cover. The cover traps gas produced during decomposition of the manure. Covered lagoon digesters are used for liquid manure (less than 2 percent solids) and require large lagoon volumes. This type of digester is the least expensive of the three.

Covered lagoon digesters typically have a hydraulic retention time (HRT) of 40 to 60 days. The HRT is the amount of time a given volume of waste remains in the treatment lagoon. A collection pipe leading from the digester carries the biogas to either a gas treatment system such as a combustion flare, or to an engine/generator or boiler that uses the biogas to produce electricity and heat. Following treatment, the digester effluent is often transferred to an evaporative pond or to a storage lagoon prior to land application.

Climate affects the feasibility of using covered lagoon digesters to generate electricity. Covered lagoon digesters are most appropriate for use in warm climates if the biogas is to be used for energy or heating purposes.

A complete mix digester is suitable for manure that is 2 percent to 10 percent solids. Complete mix digesters process manure in a heated tank above or below ground. A mechanical or gas mixer keeps the solids in suspension. However, complete mix digesters are expensive to construct and cost more than a plug-flow digester to operate and maintain.

-9-

Complete mix digester systems consist of a mix tank, a complete mix digester and a secondary storage or evaporative pond. The mix tank is either an aboveground tank or concrete in-ground tank that is fed regularly from under-floor waste storage below the animal feedlot. Waste is stirred in the mix tank to prevent solids from settling in the waste prior to being fed to the digester. The complete mix digester is essentially a constant-volume covered lagoon that is fed daily from the mix tank. Complete mix digesters with in-ground lagoons often employ covers similar to those used in covered lagoon digesters. In the digester, a mix pump circulates waste material slowly around the heater to maintain a uniform temperature. Hot water from an engine/generator co-generation water jacket or boiler is used to heat the digester. A cylindrical above-ground tank, optimizes biogas production, but is more capital intensive than in-ground tanks.

Complete Mix Digesters – A Methane Recovery Option for All Climates. Complete mix digesters have an HRT of 12 to 20 days, which means that complete mix digesters can reduce the overall lagoon volume required for waste storage and treatment. This makes complete mix digesters comparable to covered lagoon digesters in cost, despite the increased complexity of stirring, mixing and plumbing components. In addition, biogas production rates, and therefore heat and electricity production, are greater and more consistent than for covered lagoons. This can help reduce system payback periods compared to covered lagoon systems. Like covered lagoon systems, digester effluent from complete mix digesters is frequently stored in evaporative ponds or storage lagoons.

Plug-flow digesters, are suitable for ruminant animal manures having a solids concentration of 11% to 14%. In a plug-flow digester, raw manure slurry enters one end of a rectangular tank and decomposes as it moves through the tank. New material added to the tank pushes older material to the opposite end. Coarse solids in ruminant manure form a viscous material as they are digested, limiting solids separation in the digester tank. As a result, the material flows through the tank in a "plug." Anaerobic digestion of the manure slurry releases gas as the material flows through the digester. A flexible, impermeable cover on the digester traps the gas.

A plug-flow digester requires minimal maintenance. Inside the digester, suspended heating pipes allow hot water to circulate. The hot water heats the digester to keep the slurry at 25°C to 40°C, a temperature range suitable for methane-producing bacteria. The hot water can come from recovered waste heat from an engine generator fueled with digester gas or from burning digester gas directly in a boiler.

The plug-flow digester design offers a high-temperature variation. High temperature speeds the digestion process and reduces the required volume of the tank by 25% to 40%. However, there are more species of anaerobic bacteria that thrive in the temperature range of a standard design (mesophillic bacteria), than there are species that thrive at higher temperatures (thermophillic bacteria). High-temperature digesters also are more prone to upset because of temperature fluctuations, and their successful operation requires close monitoring and diligent maintenance.

Digester Designs

The primary purpose of these anaerobic digesters is waste (sewage) treatment and fertilizer production. Biogas production is secondary. Anaerobic digesters are made out of concrete, steel, brick, or plastic. They are shaped like silos, troughs, basins or ponds, and may be placed underground or on the surface. All designs incorporate the same basic components: a pre-mixing area or tank, a digester vessel(s), a system for using the biogas, and a system for distributing or spreading the effluent (the remaining digested material).

For the optimum design and efficient operation of the anaerobic digester following factors helps:

1. Optimum Retention Time.

2. Adequate mixing.

3. Proper pH (6.5 –7.6)

4. Proper Temperature Control.

5. Adequate concentration of proper nutrients (BOD: N: P = 100: 2.5: 5).

6. Absence of toxic materials, and

7. Proper feed characteristics.

EFFLUENT/ DIGESTATE UTILISATION

The material drawn from the digester is called sludge, or effluent or digestate. Anaerobic digestion draws carbon, hydrogen and oxygen from the organic matter. Essential plant nutrients (N, P and K) remain largely in the digestate/effluent. The composition of the fertilizing agents depends on the organic matter and can therefore vary. The availability of nutrients is higher in digestate than in untreated organic waste, also it benefits the humus balance in the soil. Thus it can be used fertilizer or soil amendment in agriculture, landscaping. Such use permit the creation of a nutrient cycle and maintains or improves soil structure due to the application of organic matter.

The digestate may have to be dewatered and thus separated into two fractions: the fibre and the liquor.

The fibre is bulky and contains a low level of plant nutrients. It can be used as a soil conditioner and as a low-grade fertilizer and also as alternative to peat as well. Further processing of the fibre, such as through composting could produce good quality compost.

The liquor (liquid effluent) contains a large proportion of nutrients and can be used as a fertilizer. Its high water content facilitates its application through conventional irrigation methods, representing an advantage over compost as it can be applied throughout the crop cycle. The liquor is generally used on the farms on which it was produced. It has advantage over raw manure applications, as the ammonia uptake by plans is higher than for organic nitrogen.

ADVANTAGES OF AD

AD contributes to reducing the greenhouse gases. A well-managed AD system will aim to maximize methane production, but not release any gases to the atmosphere, thereby reducing overall emissions. AD also provides a source of energy with no net increase in atmospheric carbon which contributes to climate change.

The organic matter for AD also a renewable source, and therefore does not deplete finite fossil fuels. Energy generated through this process can help reducing the demand for fossil fuels. The use of the digestate also participates to this reduction by decreasing synthetic fuels use in fertilizer manufacturing, which is an energy intensive process.

AD creates an integrated management system, which reduces the likelihood of soil and water pollution to happen, compared to disposal of untreated animal manure/slurries. The treatment can also lead to a reduction up to 80% of the odour and it destroys virtually all weed seeds, thus reducing the need for herbicide and other weed control measures.

On a financial aspect, the advantage of AD is to convert residues to potentially saleable products: biogas, soil conditioner, and liquid fertilizer. It can also contribute to the economic viability of farms by keeping costs and benefits within the farm if the products are used on-site.

DISADVANTAGE OF AD

AD projects, as with many developments, will create some risks and have some potential negative environmental impact. These need to be removed wherever possible or at least minimized.

AD has significant capital and operational costs. It is unlikely that AD will be viable as an energy source alone and therefore must be seen as an integrated system. It is likely to be cost effective for those who can use the other products of AD: better waste management fertilizer.

-13-

All waste management systems create traffic movement. This can become a problem in centralized AD plants and alternative methods of transport should be investigated as transport greatly influences costs and emissions. The location of the plant should be chosen carefully so that distances traveled are minimized between the production of the organic matter, the storage tanks and the digester. Nuisance for the neighborhoods has also to be taken into account.

About health and safety, there may be some risks to human health with the pathogenic content of the organic matter but it can be avoid with an appropriate plant design and organic matter handling procedures. There may also be some risks of fine and explosion, although no greater than for natural gas installation.

APPLICATIONS

Applications such as: waste treatment, reducing pollution, odours and disease; recycling of nutrients back to the soil (thereby reducing the requirements for artificial fertilizers); improved soil quality by recycling the organic matter as humus, thus preserving fragile top soils; sanitization of the compost, reducing the spread of soil-borne pathogens and weeds.

Anaerobic digestion is particularly suited to wet, organic wastes. As such it has been used in the water industry for sewage treatment since the end of the last century. Most large sewage treatment works use the process, recovering the biogas to meet on-site heat and power requirements.

Household waste is made up of a range of materials including paper, card, plastics, textiles, glass, metal and putrescibles (organic material that is easily degraded such as fruit and foodstuffs). Of these, only putrescibles and paper are ideally suited to anaerobic digestion and the process will be easier to manage if these wastes comprise the only feed to the system.

Garden waste may also be treated by anaerobic digestion, but the extent of degradation will vary according to the type of material.

At Freiburg, Germany, cow manure is scraped and fed into a plug flow digester. The biogas produced is used to fire an 85 kW gas engine. The engine operates at 35 kW capacity levels and drives a generator to produce electricity. Electricity and heat generated is able to fulfill all dairy energy demand. The system has been in operation since 1982.

Fig 5: Anaerobic digestion plant (Freiburg, Germany) processes 36,000 tonnes waste per year, producing 3 million m³ gas and 15,000 tonnes compost.

Anaerobic digestion technology is available to produce and recover biogas from biodegradable organic matters. Three commercial technologies are available and have been operated successfully throughout the world to treat a wide range of industrial wastes.

The Anaerobic digestion process can only degrade the organic fraction of the organic matter. The implication of this is that not all waste streams are amenable to anaerobic digestion. In addition, anaerobic digestion is not the technology that can solve all the problems of waste.

It is a biological process and this places constraints on the operation of the process and how quickly it can respond to changes. The process requires conditions within the process to be stable, with either mesophilic (35°C) and thermophilic (55°C) temperatures and at moisture contents above 60%. The micro-organisms can be killed off by extremes of process conditions or toxic chemical and also require time to grow to sufficient populations to carry out the treatment. However, as a biological process the methane product is much purer than could be achieved by chemical means.

Thus, anaerobic digestion is an engineered process that requires management to obtain the best from the process.

CARTOGRAPHY

noreply@blogger.com (Civil Engineer) — Sat, 19 Jun 2010 06:34:00 +0530

Cartography is an art, science and technology of creating maps together with their study as scientific documents. Maps are graphic representation of geographical environment. Map-making process is a series of information transformation, each of which has the power to alter the appearance of final product. The fundamental function of a map is to bring things into view. All maps are concerned with two elements of reality namely location and attribute. From these two basic elements, any relationship can be formed which depends on the purpose of map.

Creating a map depends largely on its intended use. Depending upon the purpose, maps can be classified into general reference maps; and thematic maps. General reference maps show the location of a variety of different features like roads, rivers, political boundaries etc. Thematic maps concentrate on the distribution of a single and multiple attributes or the relationship among several attributes. Thematic maps tell about a theme. A simple example for a thematic map is a map used for weather forecasting.

Traditional surveying methods, which were used for cartography, are laborious and time consuming. Also the accuracy of traditional methods is low. Cartography is in the midst of a revolution in technology. This revolution is referred to as digital cartography. It is caused by widespread use of electronics and computers in the field of cartography. Increasing use of cartographic products is another factor for this revolution. This paper is an attempt to explain the new trends in cartography. This paper also deals with a brief history of cartography.

The oldest known maps are preserved on Babylonian clay tablets, which dates back to 2300 B.C. The concept of a spherical Earth was well known among Greek philosophers at the time of Aristotle (350 B.C.) and has been accepted by all geographers since.

Babylonians were the first to use sexagesimal system. Around 1320 B.C., Egyptians developed accurate system of land surveying. Greeks developed the foundation of modern cartography. They were first to develop concept of latitude and longitude. Around 400 B.C., Romans developed many military maps based on flat-earth concept. Around 1300, the use of magnetic compass in cartography was brought to western world from china. There was an end to speculative mapping from 1650 onwards. Cartographers began to explore the power of electronics in early 1950’s.

When data collection is discussed in cartography, an important term comes into picture “Ground control points”. Ground control points are fixed points, which are used to determine two or three-dimensional positions of an object. This paper deals with data collection by satellite remote sensing method.

After data has been collected the actual cartographic process starts. The data will be fed into the computer database and analysis of data and design of maps are done. After this the map is scaled according to the requirements and a suitable map projection is chosen to view the map on the computer or a hardcopy can be obtained. Choosing a map projection is very important because the resulting map should have minimum distortion.

SATELLITE REMOTE SENSING

Remote sensing is the process for collecting, storing, and extracting environmental information from images of the ground acquired by devices not in direct physical contact with the features being studied. Remote sensing devices detect and record radiant energy. Remote sensing of land surface features is based on detection of radiant energy called electromagnetic radiation. Visible light is an example of radiant energy.

All objects with temperatures above absolute zero continuously emit a broad range of electromagnetic wavelengths and frequencies. The range of electromagnetic wavelengths and frequencies can be termed as electromagnetic spectrum. The electromagnetic spectrum has been divided into energy regions. It’s as shown in the figure below. Remote sensing devises operate in all energy regions except radio, x-ray and gamma ray.

Remote sensing instruments detect and record the energy of photon in the band or bands to which the sensors is sensitive. The amount of energy detected depends on the inherent energy of photons in the band and on the number of photons reaching the detector during the short time interval of energy collection. The number of photons reaching the detector varies according to the amount of energy emitted by the illumination source, the amount of energy absorbed by the atmosphere and the degree to which ground objects reflect and emit energy.

The portions of the electromagnetic appropriate for remote sensing are restricted by atmospheric absorption. This atmospheric absorption reduces the percentage of energy transmitted through the atmosphere to the ground and back through the atmosphere to the sensing instrument. Portion of low absorption, called atmospheric windows, are the portions of the spectrum used for remote sensing using multispectral scanners. Spectral signatures of objects are identified and mapped by remote sensing methods. The figure below shows the atmospheric window where remote sensing is possible.

Satellite is used as a platform for remote sensing devices. All the satellites used for remote sensing are sun synchronous satellites. Indians are considered pioneers in remote sensing space technology. Indian space research organization (ISRO) has launched IRS satellites; the data received by these are used for various purposes in India and abroad. For example IRC-P5 (CARTOSAT-1) caters to the needs of cartographers and terrain modelling applications. The satellite will provide cadastral level information up to 1:5000 scale and will be useful for making 2-5m contour maps.

Images created by a variety of remote sensing devices are used in map compilation and updating. Remote sensing images are also geometrically rectified and mosaicked to form planimetrically correct photomaps. Energy can be recorded photographically and electronically, and the record may be in hardcopy or digital data file format.

Cartographers should understand the basic operation of major remote sensing instruments and be well acquainted with the forms of imagery each creates.

Photographic imaging

Aerial cameras, which were first developed during World War I, have long provided aerial photographs for topographic map compilation and resource inventories. The standard mapping camera produces individual large-format 9x9inch. High precision 6-inch or 12-inch focal length lenses can be used to minimize spatial distortions on the photo. The geometric accuracy of aerial photographs depends on the camera and lens design. Photo appearance and resolving power depend primarily on the type of film used.

Photographic films are composed of a transparent plastic base coated on one side with an emulsion of silver salt crystals. These crystals are sensitive to electromagnetic energy. The emulsion is exposed to photons reflected from ground objects and focused by the camera lens. Sliver crystals struck by a sufficient number of photons change their chemical properties so as to turn black upon film development. Other crystals exposed below this energy level remain in their original state. Photographic emulsion can record energy between 0.3 and 1.2mm or from the near-UV through the near-IR. Four emulsions – panchromatic, black and white infrared, true-colour, and colour-infrared have been developed for remote sensing within this spectral range.

Electronic imaging

Photographic film emulsion used in remote sensing can only be made sensitive to energy in the 0.3-1.2mm range. In all other regions of the electromagnetic spectrum, we must use electronic detection and recording instruments.

The three forms of imaging instruments currently in use are termed matrix array, pushbroom, and whiskbroom. These terms roughly describe the way these instruments create images. The basic principle of working is the same. Electronic sensors measures the intensity of radiation striking its surface, converts the intensity to a digital number, and transmits this number to a large hard disk in the control computer.

Thermal scanners are whiskbroom instruments that detect middle-IR energy in the 3-14mm range. The detector is sensitive to the temperature of the scanning device as well as to energy from the ground. Therefore, the entire instrument must be cooled with liquid nitrogen to an extremely low temperature and enclosed in a heatproof box. Since thermal scanners do not operate in the visible region, they may be used to record the nearly equal mixture of reflected and emitted thermal IR energy during the day, or emitted energy alone at night. These are used to detect forest fires, fresh lava, discharge form power plants, soil moisture differences etc.

Multi spectral scanners simultaneously record electromagnetic energy in several narrow spectral bands. Most multi spectral scanners are similar in design to the whiskbroom scanner. These are used in study of crops, natural vegetation types, soil moisture variations and land use.

Passive microwave sensors detect and record energy in the 0.1-25 cm band of the microwave region. Passive microwave sensors are similar to whiskbroom scanners except that detection of microwave energy requires an antenna device called microwave radiometer. Passive microwave images are used to map soil moisture, ocean surface conditions, inventorying the water content of snow fields, delineating the location of ice-water boundaries, and distinguishing among geologic strata.

IMAGE PROCESSING

Image processing refers to manual and digital techniques used to improve geometry, enhance image appearance, identify feature in an image, and extract selected information from an image. Cartographers use digital image processing systems to geometrically rectify images, prepare contrast enhanced multicolour image maps, create thematic maps by extracting information from image data, and simplify such thematic maps. Before this the image should be in raster format. In raster format each image is identified by a matrix of pixels.

Original image must be rectified to match a particular map projection surface or grid coordinate system laid over the projection surface. Mathematical equations are used for linear coordinate transformation. Image rectification involves placing satellite image on to a base map so that the coordinate system can be used for the satellite image.

Image enhancement is done to improve the appearance of image data displayed. Image contrast can be improved by using spatial filter, density slicing, and image combination.

THEMATIC INFORMATION EXTRACTION

The extraction of thematic information from digital image data is a very important image processing activity. There are two general approaches to compiling thematic maps through image processing namely manual image classification and digital image classification.

Digital image classification involves use of image processing software, which classify each pixel, based on the reflectance value in each spectral band. Cartographers perform two major forms of digital image classification namely supervised and unsupervised classification. Supervised classification involves determination of the digital reflectance characteristic of pixels known to be of each feature class. Unsupervised classification is based on finding inherent clusters of similar reflectance values. Digital image simplification can be done according to the requirements. In this way enhance image maps can be produced.

APPLICATIONS OF REMOTE SENSING

· Used to create digital terrain models, which are used to study topographical details.

· Used to study soil and rock types.

· Used in highway design.

· Digital maps created by remote sensing method can be used with GIS for studying

the variation of an attribute or to find relationships among them.

· Integration of thematic maps through GIS for identification of ground water potential zones.

· Used for weather forecasting.

SOIL STABILISATION

noreply@blogger.com (Civil Engineer) — Sun, 13 Jun 2010 19:32:00 +0530

Stabilization in a broad sense incorporates the various methods employed for modifying the properties of a soil to improve its engineering performance. Stabilization is being used for a variety of engineering works, the most common application being in the construction of road and airfield pavements, where the main objective is to increase the strength or stability of soil and to reduce the construction cost by making best use of locally available materials.

Principles Of Stabilization:

Natural soil is both a complex and variable material. Yet because of its universal availability and its low cost winning it offers great opportunities for skilful use as an engineering material.

Not uncommonly, however the soil at any particular locality is unsuited, wholly or partially, to the requirements of the construction engineer. A basic decision must therefore be made whether to:
• Accept the site material as it is and design to standards sufficient to meet the restrictions imposed by its existing quality.
• Remove the site material and replace with a superior material.
• Alter the properties of existing soil so as to create a new site material capable of better meeting the requirements of the task in hand.

The latter choice, the alteration of soil properties to meet specific engineering requirements is known as “Soil stabilization.”

It must also be recognized that stabilization not necessarily a magic wand by which every soil property is changed for the better. Correct usage demands a clear recognition of which soil properties must be upgraded, and this specific engineering requirement is an important element in the decision whether or not to stabilize. Properties of soil may be altered in many ways, among which are included chemical, thermal, mechanical and other means.

The chief properties of a soil with which the construction engineer is concerned are: volume stability, strength, permeability, and durability.
Methods of stabilization may be grouped under two main types:
1. modification or improvement of a soil property of the existing soil without any admixture.
2. Modification of the properties with the help of admixtures.

Compaction and drainage are the examples of the first type, which improve the inherent shear strength of soil.
Examples of the second type are: mechanical stabilization, stabilization with cement, lime, bitumen and chemicals etc,.

LIME STABILIZATION:

Stabilization of soils with hydrated lime is applicable to far heavier clayey soils and is less suitable for granular materials and second it is used more widely as a construction expedient that is to prepare a soil for further treatment or to render a sufficient improvement to support construction traffic. As a temporary measure such modification or stabilization need not necessarily affected to the standards required for permanent construction. Quick lime or lime slurries may also be used for excessively wet or dry conditions respectively. It is therefore a very versatile stabilizer.

In roads lime stabilization is widely used for sub-base construction or sub grade improvement; nevertheless there is no sound reason why these roles should not be interchangeable.

MATERIALS:

The materials to be considered are lime, soil and water and it is important that the type of lime to be used is clearly defined. It is unfortunate that the term “lime” is used to describe calcium hydroxide (agricultural lime) calcium hydroxide (slaked lime or hydrated lime) and calcium oxide (quick lime). The term is used here and in general engineering practice to mean hydrated lime.

LIME:

Calcium hydroxide is most widely used for stabilization. The stabilizing effects ultimately depend on chemical attack by the lime on clay minerals in the soil to form cementitius compounds (calcium silicate) and carbonate doesn’t do this. Lime is prepared by heating calcium carbonate (natural limestone) in kilns until carbon dioxide is driven off. The calcium oxide discharged from the kiln is known as “Quick lime” and because of lumpy condition and high heat of hydration, which makes it difficult to handle and store, particularly in humid climates it is usual slake the quick lime immediately forming hydrated lime (calcium hydroxide) as very fine powder. It is important to note that the hydration process involves a large reduction in density and this expansion is the basis of deep stabilization techniques using lime piles. Hydrated lime poses much less of a storage problem as it is no longer so susceptible to humidity: but both forms will revert to carbonate on prolonged exposure to air. The mean particle size is about 1/10th that of cement. On addition of lime to soil two main types of chemical reaction occur:

• Alteration in the nature of the absorbed layer through base exchange phenomenon and
• Cementing or puzzolanic action.

Lime reduces the plasticity index of highly plastic soils making them more friable and easy to be handled and pulvarised. The plasticity index of soils of low plasticity generally increase in the optimum water content and a decrease in the maximum compacted density, but the strength and durability increases.

The amount of lime required may be used on the unconfined compressive strength or the CBR test criteria. Normally 2 to 8% of lime may be required for coarse grained soils and 5 to 10% for plastic soils.

SPECIFICATION REQUIREMENTS FOR LIME

Property Lime
Quick lime
(Cao) Hydrated lime
(Ca(OH)2)
Calcium and magnesium oxides
Carbon dioxides-at kiln
-elsewhere

Fineness

Not less than 92 percent

Not more than 3 percent
Not more than 10 percent
Not less than 95 percent

Not more than 5 percent
Not more than 7 percent

Not more than 12 percent on 180*180
Cement standard sieve.

Construction Sequence for Lime Stabilized Bases:

1. Shaping the Sub-grade and scarifying the soil.
2. pulvarising the soil.
3. Adding and mixing lime.
4. Compacting.
5. Finishing
6. Curing.
7. Adding wearing surfacing

There are three methods for carrying out these operations:

• Mix in place method
• Traveling plant
• Stationary plant method.

Mix in place method:
In this method, the subgrade is first shaped to the required grade and is cleared of undesirable materials. It is then scarified to the required depth of treatment and the soil is pulvarised until atleast 80% of the material (excluding stones) passes a 4.75mm sieve. If another soil is to be blended, it is mixed with the loose, pulvarised soil. The pulvarised soil is spread and shaped to proper grade. Calculated amount of lime is then evenly distributed over the surface and intimately mixed. Water is added as required for compaction and the soil lime water is turned into an intimate mixture. No strict time limitation for completion of job is however necessary since soil lime cementation reactions and are slow. It is fairly easy to process coarse grained soil. Adding lime in proportions of1 to 4% can facilitate Pulvarisation and mixing of plastic clays.

Mix in place method is considered cheaper and more adaptable to different field conditions, but the processing of soil is not so thorough and accurate as with other methods.

Traveling Plant method:

In this method, the pulvarised soil is heaped into a window and the lime is spread on the top. An elevator to a mixer carried on a traveling platform where water is added and mixing is done lifts the soil and lime. The mixture is then discharged on to the subgrade. It is spread with a grader and compacted. A uniform subgrade surface with controlled depth of treatment is possible. The plant is however costly.

Stationary plant method:
In this method, the excavated soil is brought to a stationary mixing plant. At the plant lime and water are added and mixed with the soil. The mixture is then transported back to the desired location, dumped, spread and compacted. Similar to traveling method, the method affords an accurate proportioning of materials and thorough mixing. The method is slower and may prove expensive due to additional haulage of soil.

MIX DESIGN:

The mix design procedures start from an estimate of the likely lime requirement followed by detailed tests as necessary for the particular circumstances. These should be based on a knowledge of the appropriate properties, mechanisms criteria etc. as described below.

Properties:

The properties of lime-stabilized soils vary in a similar manner to that found with cement-stabilized soils. The differences lie mainly in the effect of additive content, the effect of time and the effect of temperature.

The unconfined compressive strength of soil lime mixtures increase with increasing lime content to a certain level usually about 8% for clay soils. The rate of increase then diminishes until no further strength gain occurs with increasing lime content: in contrast to cement stabilization where the increase in strength continues to quite high cement contents (20%) (Fig 5.1). Because with lime soil mixtures there is no rapid cementation akin to the setting of concrete the effect of delay in compaction is far less important with lime stabilization (fig 5.2) and indeed, an enhanced stabilizing effect may be obtained by leaving the material loose or by breaking up lightly compacted material and recompacting after 24-hours delay. Because there is, in general no urgency for compaction, the process of lime stabilization is more flexible in the field. However it was pointed out that where a rapid increase in optimum moisture content occurs as a result of lime stabilization “it may be more economical to compact quickly than to add extra water”.

The gain in strength with time of a compacted soil-lime mixture broadly follows the pattern for soil-cement mixtures (fig 5.3) but the effect of temperature is more marked. The more rapid gain in strength with increasing temperature may be one reason for the widespread use of lime in warmer climates.

Lime has an almost instantaneous effect in most cases on the plasticity of a clay(fig 5.4) and therefore upon the strength. Figure 5.5 shows a four-fold increase in strength after six minutes for clay mixed with lime: by contrast the change in strength with cement is delayed until the initial hydration set takes place. Lime improves texture, rendering a clay more workable, so much so that lime stabilization is often used for this purpose alone in clayey soils as a preliminary to shaping and compaction or to cement stabilization without regard to any possible strength increase in the compacted state.

Reaction Mechanism

Lime reacts with the clay minerals of the soil, or with any other fine, pozzolanic component such as hydrous silica, to form a tough water-insoluble gel of calcium silicate, which cements the soil particles. The cementing agent is thus exactly the same as for ordinary Portland cement, the difference being that with the latter the calcium silicate gel is formed from hydration of anhydrous calcium silicate (cement) whereas with the lime the gel is formed only after attack on and removal of silica from the clay minerals of the soil. The with contrast cement stabilization is that the latter is essentially independent of soil type: as illustrated by fig 5.6 which shows the rate of gain of strength for cement stabilized soils is different for each soil type.

The silicate gel proceeds immediately to coat and to bind clay lumps in the soil and to block off the soil pores in the manner shown by fig 5.7. In time, this gel gradually crystallizes into well defined calcium silicate hydrates such as tobermorite and hillebrandite, the microcrystals of which can also interlock mechanically. Note that reaction proceeds only whilst water is present and able to carry calcium and hydroxyl ions to the clay surface (i.e. whilst pH is still high). The reaction thus ceases on drying, and very dry soils will not react with lime. (Or cement).
The mechanism of the reaction can be represented thus:

NAS4H + CH --- NH + CAS4 H -- NS + degradation product

Where S = Sio2 H = H2O A = Al2O3 C = CaO N = Na2O

Criteria:

The criteria developed for soils treate with lime fall into two broad groups as does the usage of the material. Where the lime treatment aimed at “modifying” the soil properties by reducing plasticity improving workability increasing grain size etc.. The lime treatment is aimed at permanent and substantial “stabilization” of a soil then the criteria are based on strength bearing capacity etc..
Lime modification of soil has been used for three main purposes: to reduce the plasticity of an otherwise acceptable mechanically stable material to improve the workability of a soil and its resistance to deflocculation and erosion and to produce a rapid increase in strength in wet clay soil as a construction expedient. Criteria are not always available to measure the adequacy of the treatment. For the first named purpose the liquid and plastic limit and plasticity index are determined with varying amounts of lime added to the soil until the normal plasticity requirements for an untreated material are met. In most cases there would be in addition an increase in UCS and bearing capacity but this is not usually taken into account.

The procedure for evaluating the effectiveness by plasticity changes may be misleading, however, in kaolinitic or illitic soils where only small and slow changes in plasticity index occur. For these soils a better procedure is to adopt a strength test.

SUGGESTED CRITERIA FOR SOIL-LIME

Process Purpose Requirement
Lime “modification” Improvement of access on wet site.
Improvement of workability and pulvarization. Large increase in plastic limit. Rapid increase in bearing strength.
Large and rapid decrease in plasticity increase in proportion passing 3/16 in. sieve.
Lime “stabilization” Improvement of subgrade material.
Improvement of base material. Increase in bearing capacity
Decrease in swell
Decrease in plasticity
Increase in strength or bearing capacity (min CBR 880).

SUGGESTED LIME CONTENTS

Soil Type Content for modification Content for Stabilization
Fine crushed rock
Well graded clay gravels
Sands
Sandy clay
Silty clay
Heavy clay
Very heavy clay
Organic soils 2-4 percent
1-3 percent

Not recommended
Not recommended
1-3 percent
1-3 percent
1-3 percent
not recommended Not recommended
~3 percent

Not recommended
~ 5 percent
2-4 percent
3-8 percent
3-8 percent
not recommended

Design Procedure:

Mix design therefore, consists of adding varying amounts of lime to the soil and observing the effect, after a suitable curing period. on the plasticity, aggregations, strength or bearing capacity, when a suitable additive level may be determined. A useful guide is to allow 1 percent of lime (by weight of dry soil) for each 10 percent of clay in the soil. For closer determination, two samples prepared at _+- 2 percent of this lime content will usually reveal the optimum economic percentage. While the changes in plasticity are accepted fairly readily, there is, unfortunately, a conservative attitude to the improvements in strength, bearing capacity and stress-strain behavior.

Addition of lime to a soil with inadequate mechanical stability will improve strength, bearing capacity and resistance to water softening. In clay soils, lime will often cause rapid changes in plasticity and this in effect will “dry out” the soil. This is the basis of the use of lime stabilization as a construction expedient or for pre-treatment prior to cement stabilization. Lime stabilization is in general more tolerant of construction delay than cement stabilization and more suitable for clay soils.

SILICA FUME

noreply@blogger.com (Civil Engineer) — Sun, 13 Jun 2010 19:29:00 +0530

The use of pozzolanic materials is an old as that of the art of concrete construction. it was recognised long time age, that the suitable pozzolns used in appropriate amount, modify certain properties of fresh and hardened mortars and concretes.

It has been amply demonstrated that the best pozzolans in optimum proportions moxed with portland cement improves many qualities of concrete, such as :

· Lower the heat of hydration and thermal shrinkage ;

· Increase the watertightness;

· Reduce the alkali- aggregate reaction;

· Improve resistance to attack by sulphate soils and sea water;

· Improve extensibility;

· Lower gusceptibility to dissolution and leaching;

· Improve workability;

· Lower costs.

Pozzolanic materials are siliceous or siliceous and aluminous materials, which in themselves possess little or no cementitious value, but will , in finely divided form and in the presense of moisture, chemically react with calcium hydroxide liberated on hydration, at ordinary temperature, to form compounds, possessing cementitious properties.

What is Silica fume?

Silica fume is a by-product from electric are furnaces used in the manufacture of silicon metal of silicon alloys. The material, which contains more than 80% silica in no crystalline state and in the form of extremely fine particles (0.1 um average diameter), is highly pozzolanic. This product is excellent for use as a Portland cement supplement In addition to economic and energy saving potential, the use of pozzolanic admixtures in concrete leads to several technical advantages, such as reduction in thermal cracking caused by heat of cement hydration, improved durability to attack by sulphate and acidic waters, and high ultimate strength.

Unlike other by- product pozzolans such as fly ashes, a unique feature of CSF is that it has a better faster pozzolonic action.

How silica fume works...

CEMENTITIOUS COMPOUNDS

In cementitious compounds, silica fume works on two levels, the first one described here is a chemical reaction called the "pozzolanic" reaction. The hydration (mixing with water) of Portland cement produces many compounds, including calcium silicate hydrates (CSH) and calcium hydroxide (CH). The CSH gel is known to be the source of strength in concrete. When silica fume is added to fresh concrete it chemically reacts with the CH to produces additional CSH. The benefit of this reaction is twofold; increased compressive strength and chemical resistance. The bond between the concrete paste and the coarse aggregate, in the crucial interfacial zone, is greatly increased, resulting in compressive strengths that can exceed 15,000 psi. The additional CSH produced by silica fume is more resistant to attack from aggressive chemicals then the weaker CH.

Chemical composition of silica fume

Chemical composition of silica fume will mostly depend upon compositon of the principle product being made by furnace.additionally,the composition is also influnced by the furnace design; generally a furnace with a heat recovery system producessilica fume with lower ignition loss.the sio2 content of silica fume varies with the silica content of alloy being producer.unlike other by product pozzoloans such as fly ash,silica fume from a single source is little or no varition inchemical composition from one day to another,

Item	Requirement
Sio₂	>90%
m_go	<1.5%
SO₃	<1.1%
H₂O	<0.4%
K₂O	<2.25%
Na₂O	<1.4%
CaO	<0.35%
Si	<0.5%
Cl	<0.06%
Fe₂O₃	<2.0%

Physical characteristics

The specific gravity of CSF from silicon metal of ferrosilicon alloy industries is close to that of amorphous silica, that is approximately 2.2

The amorphous silica structure and the fine particle size re the principle reasons for the excellent pozzolanic activity of CSF, the surface area by Blaine air permeability method ranged from about 3.3 t 7.7 m2 / g The spherical shape of CSF can be confirmed by scanning electron microscopy of well- dispersed particles Figure 5.5 ) generally, the particles exist in the form of agglomerates.

Properties of fresh concrete using silica fume

Workability:-

Water demand increases in proportion to the amt of silica fume added. The increase in water demand of concrete containing silica fume is about 1% for every 1% cement substituted Workability is the ease with which a concrete mix can be handled. Water measures can be taken to avoid this increase by adjusting aggregate grading and use of super plasticizer. The addition of silica fume will lead to a cohesive mix due to more solid-to-solid contact and will have a lower slump. This reduces bleeding and segregation.

Bleeding and segregation:-

The effect of silica fume on the rheology of fresh concrete is considered a stablising affect in the sense that addition of fine particle to a concrete mix tends to reduce segregation and bleeding. When very fine particles of silica fume are added to concrete the size of flow channel is greatly reduced because these particle are able to find their way into empty spaces between 2 cement grains causing drastic segmentation of bleed water flow and reduce bleeding. Due to increase in the number of solid-to-solid contact, the cohesiveness of the concrete mix is greatly improved when silica fume is added. This makes the concrete highly attractive for pumping, shotcreting as it reduces segregation.

Time of set:-

Silica fume in small amounts (10% by weight of cement) to ordinary concrete mixtures (250 to 300 kg/ m3 cement) either has no significant effect or alters the time of set of reference concrete only slightly. For example, the data reported by pistilli et al,27 showed that the presence of 24 kg/m3 CSF (FeSi - 75 type) in a concrete mixture containing 237 kg m3 Type 1 Portland cement increased the initial and the final times of set (ASTM Method (403) by 26 min and 29 min respectively.

Plastic Shrinkage:-

Freshly placed concrete mixtures that have not vet set (i.e., that are still in a plastic state ) are prone to surface cracking due to the phenomenon known as plastic shrinkage. Since concrete containing CSF shows little or no bleeding, there are several reports confirming the sensitivity of this concrete to plastic- shrinkage, cracking when exposed to drying conditions at early age. In order to overcome this problem, the surface of concrete must be protected against evaporation as soon as possible after placement. This precaution is a part of the standard concrete curing practice in hot weather.

Properties of hardened silica fume concrete

Drying shrinkage:-

The date from drying shrinkage tests by different researchers shows that the long- term shrinkage of concrete is not affected significantly by the addition of CSF, especially when the water content of the concrete mixture has not been changed.

Creep:-

Creep of concrete is inversely proportional to strength. Since CSF is a highly pozzolanic material, it is expected that the creep of concrete containing CSF will be lower than the corresponding Portland cement concrete a reference concrete made of a calcareous aggregate and normal Portland cement, and a concrete made of the same amount of the aggregate but with 25% (by weight) cement replaced by CSF. The ratio between water to cementations material was 0.435

Examination of the 1- year creep data showed that basic creep strains were similar in both the cases: however, the drying creep strain was about 370 X 10-6 for the reference concrete compared to 300 X 10-6 for the CSF concrete

Strength charecteristic:-.

If CSF is used as an addition, there is no deleterious effect on early strengths (i.e. I- day and 3 day strengths), and a noticeable strength increase is recorded during the 3 to 28 days moist- curing period 30 when most of the pozzolanic reaction takes place. Consequently, the relative strength increase during the 28 to 90 - day period is relatively low. From the results of the investigation reported the addition of 24 kg/m³CSF to the concrete mixture containing 297 kg/m3 ASTM Type I Portland cement caused a strength increase of about 10% and 20% at 7 and 28 days, respectively; there were no differences in the strength of reference concrete and the CSF - concrete at the test ages I and 2 days.

Three series of both non air- entrained and air- entrained concrete mixtures were designed. The first contained 284kg / m³ of ASTM Type I Portland cement 0.6 ratio between water to cementations materials (i.e., Portland cement + CSF), and 0.5, 10, and 15 % cement replacement replacement by weight with CSF (94 % SiO2, 20 m2/g surface area) The second contained 340kg/m³ Portland cement 0.5 ratio between water to cementations materials, and similar levels of cement replacement with CSF as the first series. The third contained 431 kg /m³ Portland cement, 0.4 ratio between water to cementations materials.

The incorporation of CSF did not result in a significant change in compressive strength at 3 days with concretes of 0.6 and 0.5 ratio of water/ (cement+ CSF); however, the concrete with 0.4 ratio of water / (cement + CSF); showed increase in strength with increasing amount of the fume used in the test (i.e. 5 to 15 % cement replacement)

Regardless of water / (cement + CSF) ratio at 7 days and 28 days the compressive strength of concrete were increased.

All air- entrained concretes, both with and without: CSF, showed strength loss when compared with the corresponding non- air entrained concrete

DURABILITY ASPECTS

Permeability:-

Durability o a concrete to aggressive water is generally a direct function of its permeability. Manmohan and Mehta observed that highly reactive pozzolans, such as rice husk ash, are able to reduce the size of voids in hydrated cement pastes, thus making them almost impermeable even at an early age (7- 28 days) with as low as 10% additio of the pozzolan by weight of cement. a concrete moxture containing 100 kg / m3 portland cement 20% CSF, and a superplasticizer showed approximately the same permeability as a concrete containing 250 kg/m3 Portland cement but no CSF or plasticizer.

Abrasion resistance

Generally, in high- strength concrete there is a direct relationship between strength and abrasion resistance. It may be noted that exceptionally high strength in concrete cannot be achieved unless concrete is dense (low water cement ratio) and a strong aggregate has been used. The factors that have a beneficial effect on strength have also a beneficial effect on abrasion resistance. HENCE SILICA FUME CONCRETE HAS HIGH RESISTACE TO CONCRETE. A major reason for the improved resistance of concrete to acidic and sulphate waters is the reduction in the calcium hydroxide content of the cement paste which decreases linearly with the amount of CSF added. With 20% CSF by weight of cement, very little of the calcium hydroxide produced by the Portland cement hydration is left in a well hydrated cement paste.

Alkali- aggregate reaction

The amount of pozzolan needed for reducing the alkali - aggregate expansion depends on the reactivity of the pozzzolan. Whereas many researchers have reported that 30 to 40% replacement of a high- alkali Portland cement by a class F fly ash may be needed to control the alkali- aggregate expansion according to the ASTM Method C 227, even less than 10% CSF is found adequate for this purpose.

Resistance Corrosion of embedded steel

The service life of reinforced and prestressed concrete is often adversely affected by corrosion of the embedded steel. A strongly adherent iron - oxide film is usually present on the surface of steel. and this film must get disrupted before the anodic and the cathodic processes associated with the corrosion phenomenon can make sufficent progress. In some situations, such as in the presence of chloride ions, it somehow gets disrupted: this explains why cholorides are known to accelerate the corrosion of steel in concrete.

The ability of concrete to protect embedded steel from corrosion also depends on electrical resistively.

Freeze – thaw resistance

Air void stability of concrete incorporating silica fume was studied. The test results indicated that the use of silica fume has no significant influence on the production and the stability of the air void system. However freeze-thaw testing on silica fume concrete showed acceptable results. The durability was considerable greater as compared to normal concrete

Industrial Use:

Case Study 1:

The construction of New Tjorn Bridge (Figure 5.15) in Sweden is believed to be the first industrial use of CSF for obtaining both a high strength and a lower heat of hydration than otherwise would have been possible According to Rockne and Svensson45 the bridge was designed to contain some very large structural members (Pylons) of a high - strength concrete (50MPa). The use of a high content of Portland cement in the concrete mixture would have caused excessive heat of hydration with risk of thermal cracking. The principal reason for using CSF was that this permitted a deduction of the cement content without loss of strength. The average strength of concrete was 62 MPa : reduction in the Portland cement content that was made possible by the use of CSF puls the post- cooling of concrete by circulation of cold air through imbedded pipes helped to lower the peak concrete temperature by 10 to 12 C. Case Study 2CSF was used to produce a very high- strength concrete foe a high - rise building in Montreal,canada. The average compressive strength of concrete cylinders was reported to be apa at 3 days. 75 MPa at 7 days, and 90 MPa at 28 days.

Case Study 2: -

In 1980.SKW Canada. Inc., xonstructed an experimental sidewalk in Becancour (Quebec) with a concrete containing CSF. Until the time of his report in1983, thesidewalkhassurvived three Canadian winters and numerous de-icing salt applications proving durability of silica fume concrete.

Cementitious application of silica fume

High Strength Concrete

High Performance Concrete (HPC) enhanced with silica fume is so strong it becomes an economical alternative to steel. Besides providing architects and engineers with greater design flexibility, there is more usable space, since smaller columns and beams can be used in high rise buildings and long span structural designs. Other advantages include:

Tremendous compressive strengths up to 20,000 psi (140 MPa).
High modulus of elasticity exceeding 6 million psi (40,000 MPa). High flexural strengths (2,000 psi @ 28 days) for airport pavements.
Greatly reduced permeability to moisture, chlorides and chemical attack.
Increased resistance to abrasion, erosion, corrosion.
High early strengths for fast-track construction projects and precast applications.

Shotcrete

Greater economy, greater timesaving and more efficient use of sprayed concrete. Norchem silica fume produces superior shotcrete for use in rock stabilization; mine tunnel linings, and rehabilitation of deteriorating bridge and marine columns and piles. Greater bonding strength assures outstanding performance of both wet and dry process shotcreting, with greater impermeability and less rebound loss. Norchem silica fume provides improved cohesion that resists washout in tidal rehabilitation of piles and sea walls. In addition, thicker applications--up to 12 inches-- can be achieved with each pass of the nozzle. Superior performance characteristics are:

High compressive and flexural strengths.
Reduction of rebound loss up to 50%.
Improved production time, with one-pass application thicknesses up to 12 inches higher bonding strength.
High electrical resistivity and low permeability

Oil Well Grouting

Whether used for primary (placement of grout as a hydraulic seal in the wellbore) or secondary applications (remedial operations including leak repairs, splits, closing of depleted zones), the addition of silica fume enables a well to achieve full production potential. Besides producing a blocking effect in the oil well grout which prevents gas migration, it provides these advantages:

Improved flow, for easier, more effective application
Dramatically increased impermeability, for better control of gas leakage
Easier handling

Better results

The use of CSF in concrete offers many advantages; however for several reasons the indiscriminate use of the material is not recommended. Incorporation of any additional ingredients into concrete requires extra handling and storage facilities Besides cost, special precautions will be needed for batching unusual materials such as CSF, and for curing concrete containing this admixture.

Cost. Although CSF is an industrial waste, due to its fine particle size and very low bulk density the cost of shipping and handling the material is rather high. The material that is being marketed in the form of a water suspension probably costs two to three times as much.

OFFSHORE PLATFORMS

noreply@blogger.com (Civil Engineer) — Sun, 13 Jun 2010 19:26:00 +0530

Offshore structuring has become a prominent field of marine exploration, where, man has started trying his manipulation by building mesmerizing structures along and inside the oceans. These structures are susceptible to corrosion, damage caused by dropped objects, and contacts from vessels.

The technology needed to design and build deep-ocean compliant structures, such as tension leg platforms & floaters, continues to evolve to meet technical and economic needs for deepwater development. This rapid evolution in technology needs to be independently verified to ensure continued safety of operations and protection of the environment. These structures are very helpful in manufacturing marsh gases, deep oil deposits and petroleum. This paper presentation introduces you to various offshore platforms and their analysis.

The first oil offshore platform in the world is the Oil Rocks (Neft Daşları), built near Baku in Soviet Union. Building on the platform began in 1949, with Soviet Tankers transporting Oil from the first Well to Baku in 1951.The Oil Rocks lies 45–50 km (about 25 nautical miles) offshore on the Caspian Sea. The most unique feature of the Oil Rocks is that it is actually a functional city with a population of about 5000. The Oil Rocks is a city on the sea, with over 200 km of streets built on piles of dirt and landfill. Most of the inhabitants work on shifts; a week on Oil Rocks followed by a week on the shore.

Offshore platforms are used for exploration of Oil and Gas from under Seabed and processing. The First Offshore platform was installed in 1947 off the coast of Louisiana in 6M depth of water. Today there are over 7,000 offshore platforms around the world in water depths up to 1,850M.

Specifications of platforms:

Platform size depends on facilities to be installed on top side eg. Oil rig, living quarters, Helipad etc.

Classification of water depths: 350 M- Shallow water, 1500 M - Deep water, 1500 M- Ultra deep water. US Mineral Management Service (MMS) classifies water depths greater than 1,300 ft as deepwater, as and greater than 5,000 ft as ultra-deepwater.

Types of platforms:

Platforms are broadly divided as fixed and floating type platforms.

FIXED PLATFORMS:

1. Fixed Platforms: built on concrete and/or steel legs anchored directly onto the seabed, supporting a deck with space for drilling rigs, production facilities and crew quarters. Such platforms are, by virtue of their immobility, designed for very long term use (for instance the Hibernia platform). Various types of structure are used, steel jacket, concrete caisson, floating steel and even floating concrete. Steel jackets are vertical sections made of tubular steel members, and are usually piled into the seabed. Concrete caisson structures, pioneered by the Condeep concept, often have in-built oil storage in tanks below the sea surface and these tanks were often used as a flotation capability, allowing them to be built close to shore. Fixed platforms are economically feasible for installation in water depths up to about 1,700 feet (520 m).

2. Compliant Towers, consist of narrow, flexible towers and a piled foundation supporting a conventional deck for drilling and production operations. Compliant towers are designed to sustain significant lateral deflections and forces, and are typically used in water depths ranging from 1,500 and 3,000 feet (450 and 900 m).

3. Semi-submersible Platforms having legs of sufficient buoyancy to cause the structure to float, but of weight sufficient to keep the structure upright. Semi-submersible rigs can be moved from place to place; and can be ballasted up or down by altering the amount of flooding in buoyancy tanks; they are generally anchored by cable anchors during drilling operations, though they can also be kept in place by the use of dynamic positioning. Semi-submersible can be used in depths from 600 to 6,000 feet (180 to 1,800 m).

4. Jack-up Platforms, as the name suggests, are platforms that can be jacked up above the sea, by dint of legs than can be lowered like jacks. These platforms, used in relatively low depths, are designed to move from place to place, and then anchor themselves by deploying the jack-like legs.

5. Drillships, a maritime vessel that has been fitted with drilling apparatus. It is most often used for exploratory drilling of new oil or gas wells in deep water but can also be used for scientific drilling. It is often built on a modified tanker hull and outfitted with a dynamic positioning system to maintain its position over the well.

FLOATING PLATFORMS:

Floating production systems are large ships equipped with processing facilities and moored to a location for a long period. The main types of floating production systems are FPSO (floating production, storage, and offloading system), FSO (floating storage and offloading system), and FSU (floating storage unit). These ships do not actually drill for oil or gas.

1. Tension-leg Platforms, consist of floating rigs tethered to the seabed in a manner that eliminates most vertical movement of the structure. TLPS are used in water depths up to about 6,000 feet (2,000 m). The "conventional" TLP is a 4-column design which looks similar to a semisubmersible. They are relatively low cost, used in water depths between 600 and 3,500 feet (200 and 1,100 m). Mini TLPs can also be used as utility, satellite or early production platforms for larger deepwater discoveries.

2. Spar Platforms, moored to the seabed like the TLP, but whereas the TLP has vertical tension tethers the Spar has more conventional mooring lines. Spars have been designed in three configurations: the "conventional" one-piece cylindrical hull, the "truss spar" where the midsection is composed of truss elements connecting the upper buoyant hull with the bottom soft tank containing permanent ballast, and the "cell spar" which is built from multiple vertical cylinders. The Spar may be more economical to build for small and medium sized rigs than the TLP, and has more inherent stability than a TLP since it has a large counterweight at the bottom and does not depend on the mooring to hold it upright. It also has the ability, by use of chain-jacks attached to the mooring lines, to move horizontally over the oil field.

3. Normally unmanned installations are small platforms, consisting of little more than a well bay, helipad and emergency shelter. They are designed for operate remotely under normal operations, only to be visited occasionally for routine maintenance or well work.

4.FPSO: A Floating Production, Storage and Offloading vessel is a type of floating tank system used by the offshore oil and gas industry and designed to take all of the oil or gas produced from a nearby platform (s), process it, and store it until the oil or gas can be offloaded onto waiting tankers, or sent through a pipeline. A FSO is a similar system, but without the possibility to do any processing of the oil or gas. Oil has been produced from offshore locations since the 1950s. Originally, all oil platforms sat on the seabed, but as exploration moved to deeper waters and more distant locations in the 1970s, floating production systems came to be used.

Oil produced from offshore production platforms can be transported to the mainland either by pipeline or by tanker. When a tanker solution is chosen, it is necessary to accumulate oil in some form of tank such that an oil tanker is not continuously occupied while sufficient oil is produced to fill the tanker. Often the solution is a decommissioned oil tanker which has been stripped down and equipped with facilities to be connected to a mooring buoy. Oil is accumulated in the FPSO until there is sufficient amount to fill a transport tanker, at which point the transport tanker connects to the stern of the floating storage unit and offloads the oil.

PARTS OF A PLATFORM: There are 3 main parts.

1. Topside 2. Moorings and anchors 3. Risers.

TOPSIDE:

Topside is tailored to achieve weight and space saving. It is a flat opening which Incorporates process and utility equipment. namely Drilling Rig, Injection Compressors, Gas Compressors, Gas Turbine Generators, Piping, HVAC, Instrumentation, Accommodation for operating personnel, Crane for equipment handling, Helipad.

MOORINGS & ANCHORS:

These are used to tie platform in place. Anchors are usually made of steel in order to keep the structure intact. The other materials used are Steel chains, steel wire rope. If Catenary shape due to heavy weight is implemented, then the total Length of rope is more as the structural weight is high. Even synthetic fiber ropes are used. If Taut shape due to substantial less weight than steel ropes, less rope length is required and is Corrosion free

RISER:

Risers are various supports provided as link pipes. Pipes used for production, drilling, and export of Oil and Gas from Seabed. Riser system is a key component for offshore drilling or floating production projects. The cost and technical challenges of the riser system increase significantly with water depth. Design of riser system depends on filed layout, vessel interfaces, fluid properties and environmental condition. Risers Remains in tension due to self weight. Profiles are designed to reduce load on topside.

Types of risers

-Rigid

-Flexible - Allows vessel motion due to wave loading and compensates heave motion. Simple Catenary risers: Flexible pipe is freely suspended between surface vessel and the seabed.

INSTALATION OF PLATFORMS:

Since Platforms are huge structures, large cranes and computerized facilitators are required to function the machines.

BARGE LOADOUT:

Various methods are deployed based on availability of resources and size of structure. Barge Crane is the most efficient machine to unload and load the risers and topsides accurately. Flat over - Top side is installed on jackets. Ballasting of barge includes Smaller jackets can be installed by lifting them off barge using a floating vessel with cranes. Large 400’ x 100’ deck barges capable of carrying up to 12,000 tons are available as platforms or bases.

PLATFORM FOUNDATIONS:

The loads generated by environmental conditions plus by onboard equipment must be resisted by the piles at the seabed and below. The soil investigation is vital to the design of any offshore structure. Geotech report is developed by doing soil borings at the desired location, and performing in-situ and laboratory tests. Pile penetrations depend on platform size and loads, and soil characteristics, but normally range from 30 meters to about 100 meters.

Corrosion protection:

The usual form of corrosion protection of the underwater part of the jacket as well as the upper part of the piles in soil is by cathodic protection using sacrificial anodes. A sacrificial anode consists of a zinc/aluminum bar cast about a steel tube and welded on to the structures. Typically approximately 5% of the jacket weight is applied as anodes. The steelwork in the splash zone is usually protected by a sacrificial wall thickness of 12 mm to the members.

STRUCTURAL DESIGN:

Loads Design:

Offshore structure is designed for following types of loads:

– Permanent (dead) loads.

– Operating (live) loads.

– Environmental loads

Wind load

Wave load

Earthquake load

– Construction - installation loads.

– Accidental loads.

The design of offshore structures is dominated by environmental loads, especially wave load.

1. Permanent Loads:

Weight of the structure in air, including the weight of ballast. Weights of equipment, and associated structures permanently mounted on the platform. Hydrostatic forces on the members below the waterline. These forces include buoyancy and hydrostatic pressures.

2. Operating (Live) Loads: Operating loads include the weight of all non-permanent equipment or material, as well as forces generated during operation of equipment. The weight of drilling, production facilities, living quarters, furniture, life support systems, heliport, consumable supplies, liquids, etc.Forces generated during operations, e.g. drilling, vessel mooring, helicopter landing, and crane operations. Following Live load values are recommended in BS6235: Crew quarters and passage ways: 3.2 KN/m2. Working areas: 8, 5 KN/m2

3. Wind Loads: Wind load act on portion of platform above the water level as well as on any equipment, housing, derrick, etc.For combination with wave loads, codes recommend the more unfavorable of the following two loadings: 1 minute sustained wind speeds combined with extreme waves. 3 second for gusts.

When, the ratio of height to the least horizontal dimension of structure is greater than 5, then API-RP2A requires the dynamic effects of the wind to be taken into account and the flow induced cyclic wind loads due to vortex shedding must be investigated.

4. Wave load: The wave loading of an offshore structure is usually the most important of all environmental loadings. The forces on the structure are caused by the motion of the water due to the waves Determination of wave forces requires the solution of,

a) Sea state using an idealization of the wave surface profile and the wave kinematics by wave theory.

b) Computation of the wave forces on individual members and on the total structure, from the fluid motion.

Design wave concept is used, where a regular wave of given height and period is defined and the forces due to this wave are calculated using a high-order wave theory. Usually the maximum wave with a return period of 100 years is chosen. No dynamic behavior of the structure is considered. This static analysis is appropriate when the dominant wave periods are well above the period of the structure. This is the case of extreme storm waves acting on shallow water structures.

• Wave theories

Wave theories describe the kinematics of waves of water. They serve to calculate the particle velocities and accelerations and the dynamic pressure as functions of the surface elevation of the waves. The waves are assumed to be long-crested, i.e. they can be described by a two-dimensional flow field, and are characterized by the parameters: wave height (H), period (T) and water depth (d).

Wave forces on structural members

Structures exposed to waves experience forces much higher than wind loadings. The forces result from the dynamic pressure and the water particle motions. Two different cases can be distinguished:

Large volume bodies, termed hydrodynamic compact structures, influence the wave field by diffraction and reflection. The forces on these bodies have to be determined by calculations based on diffraction theory.

Slender, hydro-dynamically transparent structures have no significant influence on the wave field. The forces can be calculated in a straight-forward manner with Morison's equation. The steel jackets of offshore structures can usually be regarded as hydro-dynamically transparent

As a rule, Morison's equation may be applied when D/L < 0.2, where D is the member diameter and L is the wave length.

- Morison's equation expresses the wave force as the sum of,

– An inertia force proportional to the particle acceleration

– A non-linear drag force proportional to the square of the particle velocity.

Earthquake load: Offshore structures are designed for two levels of earthquake intensity. Strength level. Earthquake, defined as having a "reasonable likelihood of not being exceeded during the platform's life" (mean recurrence interval ~ 200 - 500 years), the structure is designed to respond elastically. Earthquake, defined as close to the "maximum credible earthquake" at the site, the structure is designed for inelastic response and to have adequate reserve strength to avoid collapse.

5. Ice and Snow Loads: Ice is a primary problem for marine structures in the arctic and sub-arctic zones. Ice formation and expansion can generate large pressures that give rise to horizontal as well as vertical forces. In addition, large blocks of ice driven by current, winds and waves with speeds up to 0.5 to 1.0 m/s, may hit the structure and produce impact loads.

6. Temperature Load: Temperature gradients produce thermal stresses. To cater such stresses, extreme values of sea and air temperatures which are likely to occur during the life of the structure shall be estimated. In addition to the environmental sources, accidental release of cryogenic material can result in temperature increase, which must be taken into account as accidental loads. The temperature of the oil and gas produced must also be considered.

7. Marine Growth: Marine growth is accumulated on submerged members. Its main effect is to increase the wave forces on the members by increasing exposed areas and drag coefficient due to higher surface roughness. It is accounted for in design through appropriate increases in the diameters and masses of the submerged members.

8. Installation Load: These are temporary loads and arise during fabrication and installation of the platform or its components. During fabrication, erection lifts of various structural components generate lifting forces, while in the installation phase forces are generated during platform load out, transportation to the site, launching and upending, as well as during lifts related to installation.

All members and connections of a lifted component must be designed for the forces resulting from static equilibrium of the lifted weight and the sling tensions.

Load out forces are generated when the jacket is loaded from the fabrication yard onto the barge. Depends on friction co-efficient

9. Accidental Load: According to the DNV rules, accidental loads are loads, which may occur as a result of accident or exceptional circumstances. Examples of accidental loads are collision with vessels, fire or explosion, dropped objects, and unintended flooding of buoyancy tanks. Special measures are normally taken to reduce the risk from accidental loads.

Load Combinations:

The load combinations depend upon the design method used, i.e. whether limit state or allowable stress design is employed. The load combinations recommended for use with allowable stress procedures are: Normal operations

Dead loads plus operating environmental loads plus maximum live loads. Dead loads plus operating environmental loads plus minimum live loads.

Extreme operation: Dead loads plus extreme environmental loads plus maximum live loads. Dead loads plus extreme environmental loads plus minimum live loads

Environmental loads should be combined in a manner consistent with their joint probability of occurrence. Earthquake loads are to be imposed as a separate environmental load, i.e., not to be combined with waves, wind, etc.

Analysis and modeling;

The analytical models used in offshore engineering are similar to other types of on shore steel structures. The same model is used throughout the analysis except supports locations. Stick models are used extensively for tubular structures (jackets, bridges, flare booms) and lattice trusses (modules, decks).Each member is normally rigidly fixed at its ends to other elements in the model. In addition to its geometrical and material properties, each member is characterized by hydrodynamic coefficients, e.g. relating to drag, inertia, and marine growth, to allow wave forces to be automatically generated.

Structural analysis: Integrated decks and hulls of floating platforms involving large bulkheads are described by plate elements. Deck shall be able to resist crane’s maximum overturning moments coupled with corresponding maximum thrust loads for at least 8 positions of the crane boom around a full 360° path. The structural analysis will be a static linear analysis of the structure above the seabed combined with a static non-linear analysis of the soil with the piles. Transportation and installation of the structure may require additional analyses detailed fatigue analysis should be performed to assess cumulative fatigue damage the offshore platform designs normally use pipe or wide flange beams for all primary structural members.

Acceptance Criteria: The verification of an element consists of comparing its characteristic resistance(s) to a design force or stress. It includes:

-a strength check, where the characteristic resistance is related to the yield strength of the element,

-a stability check for elements in compression related to the buckling limit of the element.

-An element is checked at typical sections (at least both ends and mid span) against resistance and buckling.

-Tubular joints are checked against punching. These checks may indicate the need for local reinforcement of the chord using larger thickness or internal ring-stiffeners.

-Elements should also be verified against fatigue, corrosion, temperature or durability wherever relevant

Offshore Standards (OS):

Provides technical requirements and acceptance criteria for general application by the offshore industry eg.DNV-OS-C101

Recommended Practices (RP): Provides proven technology and sound engineering practice as well as guidance for the higher level publications eg. API-RP-WSD

BS 6235: Code of practice for fixed offshore structures.

– British Standards Institution 1982.

What it is

An increasing portion of oil and gas production is coming from offshore fields. Advanced technologies now permit production from deepwater fields and from marginal fields.
In parallel, platform technologies are evolving from fixed platforms suited for shallow waters, to semi-submersible platforms (TLP, SPAR) and to Floating Production Units (FPU, FPSO). The latter reduce project lead-time, have higher performance flexibility, and may be moved from a depleted field to a new field, thus greatly reducing investments. They are the most common solution for deepwater and marginal fields.

Offshore platforms are equipped with the machinery needed to extract oil and natural gas but have some critical challenges that should not be underestimated. Thanks to its many years of worldwide experience, GE Oil & Gas can provide optimum technical solutions and the project management experience needed to maximize production while helping customers to meet or accelerate their "First Oil" date.

How it works

Offshore production platforms/FPSO collect the hydrocarbons produced under the seabed by means of specially designed flow-lines and risers. The platform also contains the necessary monitoring & control equipment, and gear for furnishing electric and/or hydraulic power to the subsea equipment installed at the various field wells.
Power generation, compression and pumping equipment are generally installed on the platform. This machinery is used to collect the hydrocarbons and convey them to onshore receiving facilities, or for the re-injection of associated gas back into the well to enhance production.

SELF COMPACTING CONCRETE

noreply@blogger.com (Civil Engineer) — Sun, 13 Jun 2010 19:18:00 +0530

When large quantity of heavy reinforcement is to be placed in a reinforced concrete (RC) member, it is difficult to ensure that the formwork gets completely filled with concrete, that is, fully compacted without voids or honeycombs. Compaction by manual or by mechanical vibrators is very difficult in this situation. The typical method of compaction, vibration, generates delays and additional cost in the projects. Underwater concreting always required fresh concrete, which could be placed without the need to compaction; in such circumstances vibration had been simply impossible.This problem can now be solved with self-compacting concrete. This type of concrete flows easily around the reinforcement and into all corners of the formwork. Self-compacting concrete (SCC) describes a concrete with the ability to compact itself only by means of its own weight without the requirement of vibration. Self-compacting concrete also known as Self-consolidating concrete or self levelling concrete.Fig.1 shows the flow of Self-compacting concrete.
Self-compacting concrete is placed or poured in the same way as ordinary concrete but without vibration. It is very fluid and can pass around obstructions and fill all the nooks and corners without the risk of either mortar or other ingredients of concrete separating out, at the same time there are no entrapped air or rock pockets. This type of concrete mixture does not require any compaction and is saves time, labour and energy. The surface finish produced by self-compacting concrete is exceptionally good and patching will not be necessary.
Self-compacting concrete has been successfully used in France, Denmark, the Netherlands and UK, apart from Japan. It is gaining wide acceptability because no vibration is needed and noise pollution is eliminated. The construction process is safer and more productive. This seminar in general deals with introduction to SCC, materials and methods of production of SCC, properties of SCC, advantages and disadvantages, furthermore in particular application of SCC is also discussed.

HISTORY OF SCC
The introduction of the “modern” self-compacting concrete (SCC) is associated with the drive towards better quality of concrete pursued in Japan in late 1980’s, where the lack of uniform and complete compaction had been identified as the primary factor responsible for poor performance of concrete structures. There were no practical means by which full compaction of concrete on a site was ever to be fully guaranteed, instead, the focus therefore turned onto the elimination of the need to compact, by vibration or any other means. This led to the development of the first practicable SCC by researchers (Okamura, Ozawa et al.) at the University of Tokyo and the large Japanese contractors (e.g. Kajima, Maeda, Taisei etc.) quickly took up the idea. The contractors used their large in-house R&D facilities to develop their own SCC technologies. Each company developed their own mix designs, trained their own staff to act as technicians for testing on sites, and tailor made their SCC mixes for large projects they tendered for. Importantly, each of the large contractors also developed their own testing devices and test methods
In the early 1990’s there was only a limited public knowledge about the SCC, mainly in Japanese, the fundamental and practical know-how was kept secret by the large corporations to maintain commercial advantage. The SCCs were used under trade names, such as the NVC (Non-vibrated concrete) of Kajima Co., SQC (Super quality concrete) of Maeda Co. or the Biocrete (Taisei Co.). Simultaneously with the Japanese developments in the SCC area, R&D continued in mix-design and placing of underwater concrete where new admixtures were producing SCC mixes with performance matching that of the Japanese SCC concrete (e.g. University of Paisley / Scotland, Univ. of Sherbrooke / Canada etc.). Modern, present-day Self-Compacting Concrete (SCC) can be classified as an advanced construction material. The SCC, as the name suggests, does not require to be vibrated to achieve full compaction. This offers many benefits and advantages over conventional concrete. These include an improved quality of concrete and reduction of on-site repairs, faster construction times, lower overall costs, facilitation of introduction of automation into concrete construction. An important improvement of health and safety is also achieved through elimination of handling of vibrators and a substantial reduction of environmental noise loading on and around a site. The composition of SCC mixes includes substantial proportions of fine-grained inorganic materials; this offers possibilities for utilisation of “dusts”, which are currently waste products demanding with no practical applications and which are costly to dispose of.
Current Indian scenario in construction shows increased construction of large and complex structures, which often leads to difficult concreting conditions. Vibrating concrete in congested locations may cause some risk to labour in addition to noise stress. There are always doubts about the strength and durability placed in such locations. So it is worthwhile to eliminate vibration in practice, if possible. In countries like Japan, Sweden, Thailand, UK etc., the knowledge of SCC has moved from domain of research to application. But in India, this knowledge is to be widespread.

MATERIALS
The Materials used in SCC are the same as in conventional concrete except that an excess of fine material and chemical admixtures are used. Also, a viscosity-modifying agent(VMA) will be required because slight variations in the amount of water or in the proportions of aggregate and sand will make the SCC unstable, that is, water or slurry may separate from the remaining material. The powdered materials are fly ash, silica fume, lime stone powder, glass filler and quartzite filler. The use of pozzolanic materials helps the SCC to flow better. The pozzolanic reaction in SCC, as well as in Conventional Slump Concrete (CSC), provides more durable concrete to permeability and chemical attacks.

To achieve a high workability and avoid obstruction by closely spaced reinforcing, SCC is designed with limits on the nominal maximum size (NMS) of the aggregate, the amount of aggregate, and aggregate grading. However, when the workability is high, the potential for segregation and loss of entrained air voids increases. These problems can be alleviated by designing a concrete with a high fine-to-coarse-aggregate ratio, a low water–cementitious material ratio (w/cm), good aggregate grading, and a high-range water-reducing admixture (HRWRA).
Following are bases which are commonly used as superplasticizers.
• Modified Lignosulfonates(MLS).
• Sulfonated Melamine Formaldehyde (SMF)
• Sulfonated Naphthalene Formaldehyde(SNF)
• Acrylic Polymer based(AP)

Coplymer of Carboxilic Acrylic
Acid with Acrylic Ester(CAE)
Cross Linked Acrylic Ploymer(CLAP)
Polycarboxylatethers(PCE)
Multicarboxylatethers(MCE)
Polyacrylates

• Combination of above
Different bases of New Generation super Plasticizers or High Water reducing agents(HRWRA) have different water reduction capacities. The advantage of this water reduction can be taken either to increase the strength as in high strength concrete or to obtain a better flowability as in case of self compacting concrete.

PRODUCTION OF SCC
Based on the original conception of Okamura and Ozawa, in general three types of SCC can be distinguished:
a) Powder type self compacting concrete: This is proportion ed to give the required self compatibility by reducing by reducing the water-powder (material < 0.1mm) ratio and provide adequate segregation resistance. Superplasticizers and air entraining admixtures give the required deformability.
b) Viscosity agent type self compacting concrete: This type is proportioned to provide self compaction by the use of a viscosity modifying admixture to provide segregation resistance.Superplasticizers and air entrainment admixtures are used for obtaining the desired deformability.
c)combination type self compacting concrete: This type is proportioned so as to obtain self compatibility mainly by reducing the water powder ratio, as in the powder type ,and a viscosity modifying admixture is added to reduce the quality of fluctuation of the fresh concrete due to the variation of the surface moisture content of the aggregates and their gradations during the production .This facilitates the production control of the concrete.

Test Methods for Self Compatibility
Conventional workability tests, devised for normal ranges of concrete mixtures are not adequate for self-compacting concrete, because they are not sensitive enough to detect the tendency to segregation. For example, a slump test may show collapse, ( a slump of say 280 mm) and yet in one case the mixture may be stable and in other cases either the aggregate may settle down or the slurry may tend to “run”. Therefore test equipment was fabricated for judging the following characteristics.
(1) Self-compatibility: The U-tube test gives an indication of the resistance of the mixture to flow round obstructions in a U-type mould, Fig 2. This test also detects the tendency of the coarse aggregate particles to stay back or settle down, when the mixture flows through closely-spaced reinforcements.
(2) Deformability: The slump flow test as specified by the Japan Society of Civil Engineers (JSCE) judges the ability of concrete to deform under its own weight against the friction of the base, Fig 3. This test, however, cannot evaluate whether the concrete will pass through the space between the reinforcement bars. This test is useful also as a routine control test, to detect the tendency for slurry to separate from the mixture.
(3) Viscosity: Viscosity of the mortar phase is obtained by a V-funnel apparatus, Fig 4.This is useful for adjusting the powder content, water content and admixture dosage.
(4) Filling ability test: It is also used to determine the ability of the concrete to deform readily through closely spaced obstacles.(fig.5)

Many different methods have been developed to characterise the properties of SCC. No single method has been found till date which characterises all the relevant workability aspects and hence, each mixed has been tested by more than one test method for the different workability parameters.
apparatus
PROPERTIES OF SCC
Hardened properties of SCC
Development of concrete strength with time: The compressive strength, as one of the most important properties of hardened concrete, in general is the characteristic material value for the classification of concrete in national and international codes. For this reason, it is of interest whether the differences in the mixture composition and positive dissimilarities in the microstructure, as mentioned before, affect the short and long term load-bearing behaviour. Accordingly, clarification is still necessary to determine whether the hardening process and the ultimate strengths of SCC and conven-tional concrete differ. After 28 days the reached compressive strength of SCC and normal vibrated concrete of similar composition does not differ significantly in the majority of the published test results. Isolated cases, however, showed that at the same water cement ratios slightly higher compressive strengths were reached for SCC. At the current time there is insufficient research to result in generalized conclusions with this fact. The comparison of hardening processes shows that the strength development of SCC and conventional concrete is similar, Fig. [6]. Some of the published test results show that an increase of the cement content and a reduction of filler con-tent at the same time increases the initial concrete strength and the ultimate concrete strength. For young SCC aged up to 7 days the relative compressive strength spreads to a greater extend as given in the CEB-FIB Model Code 90, whereas higher values as well as lower ones are reached. Especially if limestone powder is used higher compressive strengths are noticeable at the beginning of the hardening process.
Splitting tensile strength :All parameters which influence the characteristics of the microstructure of the cement matrix and of the interfacial transition zone (ITZ) are of decisive impor-tance in respect of the tensile load bearing behaviour. By evaluating the created database it could be shown, that most results of the measured splitting tensile strength values are in the range of valid regulations for normal vibrated concrete with the same compressive strength. However, in about 30% of all data points a higher splitting tensile strength was stated,

The tendency of a higher splitting tensile strength of SCC. Likely as not, the reason for this fact is given by the better microstructure, especially the smaller total porosity and the more even pore size distribution within the interfa-cial transition zone of SCC. Further on a denser cement matrix is present due to the higher content of ultrafines. The time development of tensile strength of SCC and normal vibrated concrete are subjected to a similar dependence. Only few publications about SCC refer to a more rapidly increase of the tensile strength opposite to the compressive strength.
Modulus of elasticity:As it is known, the modulus of elasticity of concrete depends on the proportion of the Young´s moduli of the individual components and their percentages by vol-ume. Thus, the modulus of elastisity of concrete increases for high contents of aggregates of high rigidity, whereas it decreases with increasing hardened cement paste content and increasing porosity. A relative small modulus of elasticity can be expected, because of the high content of ultrafines and additives as dominating factors and, accordingly, minor occurrence of coarse and stiff aggregates at SCC. Indeed, it was shown by analysing the database that the modulus of elasticity of SCC can be up to 20 % lower compared with normal vibrated concrete having the same compressive strength and made of the same aggregates. Nevertheless, it is mainly still in the range of the CEB-FIB Model Code 90,

TECHNICAL ADVANTAGES OF SELF-COMPACTING CONCRETE
Simple inclusion even in complicated formwork and tight reinforcement
• Higher installation performance since no compaction work is necessary which leads to reduced construction times, especially at large construction sites
• Reduced noise pollution since vibrators are not necessary
• Higher and more homogenous concrete quality across the entire concrete cross-section, especially around the reinforcement
• Improved concrete surfaces (visible concrete quality)
• Typically higher early strength of the concrete so that formwork removal can be performed more quickly.
APPLICATION
Current condition on application of self-compacting concrete in Japan:
After the development of the prototype of self-compacting concrete at the University of Tokyo, intensive research was begun in many places, especially in the research institutes of large construction companies. As a result, self-compacting concrete has been used in many practical structures. The first application of self-compacting concrete was in a building in June 1990. Self-compacting concrete was then used in the towers of a prestressed concrete cable-stayed Shin-Kiba Ohashi bridge in 1991. Lightweight self-compacting concrete was used in the main girder of a cable-stayed bridge in 1992. Since then, the use of self-compacting concrete in actual structures has gradually increased. Self-compacting concrete has been successfully used in France, Denmark, the Netherlands,Germany,USA and UK, apart from Japan.
• A typical application example of Self-compacting concrete is the two anchorages of Akashi-Kaikyo (Straits) Bridge opened in April 1998, a suspension bridge with the longest span in the world (1,991 meters) (Fig. 9). The volume of the cast concrete in the two ahchorages amounted to 290,000 m3. A new construction system, which makes full use of the performance of selfcompacting concrete, was introduced for this. The concrete was mixed at the batcher plant beside the site, and was the pumped out of the plant. It was transported 200 meters through pipes to the casting site, where the pipes were arranged in rows 3 to 5 meters apart. The concrete was cast from gate valves located at 5 meter intervals along the pipes. These valves were automatically controlled so that a surface level of the cast concrete could be maintained. In the final analysis, the use of self-compacting concrete shortened the anchorage construction period by 20%, from 2.5 to 2 years.
• Self-compacting concrete was used for the wall of a large LNG tank belonging to the Osaka Gas Company, whose concrete casting was completed in June 1998. (Fig.10) The volume of the selfcompacting concrete used in the tank amounted to 12,000 m3. The adoption of self-compacting concrete means that
(1) the number of lots decreases from 14 to 10, as the height of one lot of concrete casting was increased.
(2) the number of concrete workers was reduced from 150 to 50.
(3) the construction period of the structure decreased from 22 months to18 months.
Self-compacting concrete is often employed in concrete products to eliminate the noise of vibration. This improves the working environment at plants and makes it possible for concrete product plants to be located in the urban area. The annual production of concrete products using self-compacting concrete exceeded 200,000 tons in 1996 .
• Application in under water construction
40000 m3 of concrete placed under water (Fig. 11-13) by using the Tremie method for the construction of a dry dock

• SCC is made from the ingredients, which are almost same used in producing in conventional concrete. Thorough understanding of role played by each of the ingredient of SCC is essential.
• Properties of fresh and hardened SCC should be established in the laboratory before their use in the field. Even though the initial cost of SCC is comparatively higher than the conventional concrete. Considering the long service of the structure, minimum maintenance, labour cost, cost due to the vibrators required, benefit cost ratio is very much in favour in case of SCC.
• Self Consolidating Concrete, as well as Conventional Slump Concrete, requires proper mixt proportion to become a durable concrete.
• The uses of pozzolanic materials, such as slag, fly ash, silica fume, etc., will help SCC more durable, otherwise these are waste products demanding with no practical applications and which are costly to dispose of.
• The use of proper super plasticizing admixture in combination with proper air entraining admixture is the absolute key to durable concrete due to freeze-thaw and scaling resistance.
• Advantage with respect to sound pollution.
• Considerable improvements in exposed surface (Fair Faced Concrete)
• Self compacting concrete is ideal for concrete parts with complicated shapes and elements with high quality visible concrete.
• Vibrating concrete in congested locations may cause some risk to labour in addition to noise stress. There are always doubts about the strength and durability placed in such locations. So it is worthwhile to eliminate vibration in practice, if possible.
• In countries like Japan, Sweden, Thailand, U.K and U.S.A, etc., the knowledge of SCC has moved from domain of research to application. But in India, this knowledge is to be widespread.

HIGH PERFORMANCE CONCRETE

noreply@blogger.com (Civil Engineer) — Fri, 11 Jun 2010 07:04:00 +0530

High performance concrete is a concrete mixture, which possess high durability and high strength when compared to conventional concrete. This concrete contains one or more of cementious materials such as fly ash, Silica fume or ground granulated blast furnace slag and usually a super plasticizer. The term ‘high performance’ is somewhat pretentious because the essential feature of this concrete is that it’s ingredients and proportions are specifically chosen so as to have particularly appropriate properties for the expected use of the structure such as high strength and low permeability. Hence High performance concrete is not a special type of concrete. It comprises of the same materials as that of the conventional cement concrete. The use of some mineral and chemical admixtures like Silica fume and Super plasticizer enhance the strength, durability and workability qualities to a very high extent.

High Performance concrete works out to be economical, even though it’s initial cost is higher than that of conventional concrete because the use of High Performance concrete in construction enhances the service life of the structure and the structure suffers less damage which would reduce overall costs.

Concrete is a durable and versatile construction material. It is not only

Strong, economical and takes the shape of the form in which it is placed, but it is also aesthetically satisfying. However experience has shown that concrete is vulnerable to deterioration, unless precautionary measures are taken during the design and production. For this we need to understand the influence of components on the behavior of concrete and to produce a concrete mix within closely controlled tolerances.

The conventional Portland cement concrete is found deficient in respect of :

· Durability in severe environs (shorter service life and frequent maintenance)

· Time of construction (slower gain of strength)

· Energy absorption capacity (for earthquake resistant structures)

· Repair and retrofitting jobs.

Hence it has been increasingly realized that besides strength, there are other equally important criteria such as durability, workability and toughness. And hence we talk about ‘High performance concrete’ where performance requirements can be different than high strength and can vary from application to application.

High Performance Concrete can be designed to give optimized performance characteristics for a given set of load, usage and exposure conditions consistent with the requirements of cost, service life and durability. The high performance concrete does not require special ingredients or special equipments except careful design and production. High performance concrete has several advantages like improved durability characteristics and much lesser micro cracking than normal strength concrete.

Any concrete which satisfies certain criteria proposed to overcome limitations of conventional concretes may be called High Performance Concrete. It may include concrete, which provides either substantially improved resistance to environmental influences or substantially increased structural capacity while maintaining adequate durability. It may also include concrete, which significantly reduces construction time to permit rapid opening or reopening of roads to traffic, without compromising long-term servicibility. Therefore it is not possible to provide a unique definition of High Performance Concrete without considering the performance requirements of the intended use of the concrete.

American Concrete Institute defines High Performance Concrete as

“A concrete which meets special performance and uniformity requirements that cannot always be achieved routinely by using only conventional materials and normal mixing, placing and curing practices”. The requirements may involve enhancements of characteristics such as placement and compaction without segregation, long-term mechanical properties, and early age strength or service life in severe environments. Concretes possessing many of these characteristics often achieve High Strength, but High Strength concrete may not necessarily be of High Performance .A classification of High Performance Concrete related to strength is shown below.

Compressive strength (Mpa)	50	75	100	125	150
High Performance Class	I	II	III	IV	V

SELECTION OF MATERIALS

The production of High Performance Concrete involves the following three important interrelated steps:

· Selection of suitable ingredients for concrete having the desired rheological properties, strength etc

· Determination of relative quantities of the ingredients in order to produce durability.

· Careful quality control of every phase of the concrete making process.

The main ingredients of High Performance Concrete are

Cement

Physical and chemical characteristics of cement play a vital role in developing strength and controlling rheology of fresh concrete. Fineness affects water requirements for consistency. When looking for cement to be used in High Performance Concrete one should choose cement containing as little C₃A as possible because the lower amount of C₃A, the easier to control the rheology and lesser the problems of cement-super plasticizer compatibility. Finally from strength point of view, this cement should be finally ground and contain a fair amount of C₃S.

Fine aggregate

Both river sand and crushed stones may be used. Coarser sand may be preferred as finer sand increases the water demand of concrete and very fine sand may not be essential in High Performance Concrete as it usually has larger content of fine particles in the form of cement and mineral admixtures such as fly ash, etc. The sand particles should also pack to give minimum void ratio as the test results show that higher void content leads to requirement of more mixing water.

Coarse aggregate

The coarse aggregate is the strongest and least porous component of concrete. Coarse aggregate in cement concrete contributes to the heterogeneity of the cement concrete and there is weak interface between cement matrix and aggregate surface in cement concrete. This results in lower strength of cement concrete by restricting the maximum size of aggregate and also by making the transition zone stronger. By usage of mineral admixtures, the cement concrete becomes more homogeneous and there is marked enhancement in the strength properties as well as durability characteristics of concrete. The strength of High Performance Concrete may be controlled by the strength of the coarse aggregate, which is not normally the case with the conventional cement concrete. Hence, the selection of coarse aggregate would be an important step in High Performance Concrete design mix.

Water

Water is an important ingredient of concrete as it actively participates in the chemical reactions with cement. The strength of cement concrete comes mainly from the binding action of the hydrated cement gel. The requirement of water should be reduced to that required for chemical reaction of unhydrated cement as the excess water would end up in only formation of undesirable voids in the hardened cement paste in concrete. From High Performance Concrete mix design considerations, it is important to have the compatibility between the given cement and the chemical/mineral admixtures along with the water used for mixing.

Chemical Admixtures

Chemical admixtures are the essential ingredients in the concrete mix, as they increase the efficiency of cement paste by improving workability of the mix and there by resulting in considerable decrease of water requirement.

Different types of chemical admixtures are

· Plasticizers

· Super plasticizers

· Retarders

· Air entraining agents

Placticizers and super placticizers help to disperse the cement particles in the mix and promote mobility of the concrete mix. Retarders help in reduction of initial rate of hydration of cement, so that fresh concrete retains its workability for a longer time. Air entraining agents artificially introduce air bubbles that increase workability of the mix and enhance the resistance to deterioration due to freezing and thawing actions.

Mineral admixtures

The major difference between conventional cement concrete and High Performance Concrete is essentially the use of mineral admixtures in the latter. Some of the mineral admixtures are

· Fly ash

· Silica fumes

· Carbon black powder

· Anhydrous gypsum based mineral additives

Mineral admixtures like fly ash and silica fume act as puzzolonic materials as well as fine fillers, thereby the microstructure of the hardened cement matrix becomes denser and stronger. The use of silica fume fills the space between cement particles and between aggregate and cement particles. It is worth while noting that addition of silica fume to the concrete mix does not impart any strength to it, but acts as a rapid catalyst to gain the early age strength.

BEHAVIOUR OF FRESH CONCRETE

Introduction:

The behavior of fresh High Performance Concrete is not substantially different from conventional concretes. While many High Performance Concretes exhibits rapid stiffening and early strength gain, other’s may have long set times and low early strengths. Workability is normally better than conventional concretes produced from the same set of raw materials. Curing is not fundamentally different for High Performance Concrete than for conventional concretes although many High Performance Concretes with good early strength characteristics may be less sensitive to curing.

Workability

The workability of High Performance Concrete is normally good, even at low slumps, and High Performance Concrete typically pumps very well, due to the ample volume cementitious materials and the presence if chemical admixtures. High Performance Concrete has been successfully pumped even up to 80 storeys. While pumping of concrete, one should have a contingency plan for pump breakdown. Super workable concretes have the ability to fill the heavily reinforced sections without internal or external vibration, without segregation and without developing large sized voids. These mixtures are intended to be self-leveling and the rate of flow is an important factor in determining the rate of production and placement schedule. It is also a useful tool in assessing the quality of the mixture. Flowing concrete is, of course, not required in all High Performance Concrete and adequate workability is normally not difficult to attain.

Setting time

Setting time can vary dramatically depending on the application and the presence of set modifying admixtures and percentage of the paste composed of Portland cement. Concretes for applications with early strength requirements can lead to mixtures with rapid slump loss and reduced working time. This is particularly true in warmer construction periods and when the concrete temperature has been kept high to promote rapid strength gain.

The use of large quantities of water reducing admixtures can significantly extend setting time and therefore reduce very early strengths even though strengths at more than 24 hours may be relatively high. Dosage has to be monitored closely with mixtures containing substantial quantities of mineral admixtures so as to not overdose the Portland cement if adding the chemical admixture on the basis of total cementitious material.

BEHAVIOUR OF HARDENED CONCRETE

Introduction:

The behavior of hardened concrete can be characterized in terms of it’s short term and long term properties. Short-term properties include strength in compression, tension and bond. The long-term properties include creep, shrinkage, behaviour under fatigue and durability characteristics such as porosity, permeability, freeze-thaw resistance and abrasion resistance.

Strength

The strength of concrete depends on a number of factors including the properties and proportions of the constituent materials, degree of hydration, rate of loading, method of testing and specimen geometry. The properties of the constituent materials affect the strength are the quality of fine and coarse aggregate, the cement paste and the bond characteristics. Hence, in order to increase the strength steps must be taken to strengthen these three sources.

Testing conditions including age, rate of loading, method of testing and specimen geometry significantly influence the measured strength. The strength of saturated specimens can be 15 to 20 percent lower than that of dry specimens. Under impact loading, strength may be as much as 25 to 35 percent higher than under a normal rate of loading. Cube specimens generally exhibit 20 to 25 percent higher strengths than cylindrical specimens. Larger specimens exhibit lower average strengths.

Strength development

The strength development with time is a function of the constituent materials and curing techniques. An adequate amount of moisture is necessary to ensure that hydration is sufficient to reduce the porosity to a level necessary to attain the desired strength. Although cement paste in practice will never completely hydrate, the aim of curing is to ensure sufficient hydration. In general, a higher rate of strength gain is observed for higher strength concrete at early ages. At later ages the difference is not significant.

Compressive strength

Maximum practically achievable, compressive strengths have increased steadily over the years. Presently,28 days strength of up to 80Mpa are obtainable. However, it has been reported that concrete with 90-day cylinder strength of 130 Mpa has been used in buildings in US. The trend for the future as identified by the ACI committee is to develop concrete with compressive strength in excess of 140 Mpa and identify its appropriate applications.

Tensile strength

The tensile strength governs the cracking behavior and affects other properties such as stiffness; damping action, bond to embedded steel and durability of concrete. It is also of importance with regard to the behavior of concrete under shear loads. The tensile strength is determined either by direct tensile tests or by indirect tensile tests such as split cylinder tests.

DURABILITY CHARACTERISTICS

The most important property of High Performance Concrete, distinguishing it from conventional cement concrete is it’s far higher superior durability. This is due to the refinement of pore structure of microstructure of the cement concrete to achieve a very compact material with very low permeability to ingress of water, air, oxygen, chlorides, sulphates and other deleterious agents. Thus the steel reinforcement embedded in High Performance Concrete is very effectively protected. As far as the resistance to freezing and thawing is concerned, several aspects of High Performance Concrete should be considered. First, the structure of hydrated cement paste is such that very little freezable water is present. Second, entrained air reduces the strength of high performance concrete because the improvement in workability due to the air bubbles cannot be fully compensated by a reduction in the water content in the presence of a superplasticizer. In addition, air entrainment at very low water/cement ratio is difficult. It is, therefore, desirable to establish the maximum value of the water/cement ratio below which alternating cycles of freezing and thawing do not cause damage to the concrete. The abrasion resistance of High Performance Concrete is very good, not only because of high strength of the concrete but also because of the good bond between the coarse aggregate and the matrix which prevents differential wear of the surface. On the other hand, High Performance Concrete has a poor resistance to fire because the very low permeability of High Performance Concrete does not allow the egress of steam formed from water in the hydrated cement paste. The absence of open pores in the structure zone of High Performance Concrete prevents growth of bacteria. Because of all the above- reasons, High Performance Concrete is said to have better durability characteristics when compared to conventional cement concrete.

WHEN TO USE HPC

High Performance Concrete can be used in severe exposure conditions where there is a danger to concrete by chlorides or sulphates or other aggressive agents as they ensure very low permeability. High Performance Concrete is mainly used to increase the durability is not just a problem under extreme conditions of exposure but under normal circumstances also, because carbon di oxide is always present in the air .This results in carbonation of concrete which destroys the reinforcement and leads to corrosion. Aggressive salts are sometimes present in the soil, which may cause abrasion. High Performance Concrete can be used to prevent deterioration of concrete. Deterioration of concrete mostly occurs due to alternate periods of rapid wetting and prolonged drying with a frequently alternating temperatures. Since High Performance Concrete has got low permeability it ensures long life of a structure exposed to such conditions.

APPLICATIONS:

High strength and superior durability characteristics of High Performance Concrete have already been utilized in many structural applications in various countries. Some of the applications of High Performance Concrete are:

Bridges –Joigny (France), Greatbelt (Denmark), Akkegawa (Japan), Willows (Canada)

High rise buildings-Water tower plaza (US), Nova Scotia (Canada)

Tunnels-La Bauma and Villejust (France), Manche (UK)

Pavements-Valerenga (Norway), Highway 86,Paris airport (France)

Nuclear structures-Civeaux (France)

CASE STUDY

Joigny Bridge:

After extensive research and development in French laboratories, the French ministry of public works and the national project on New concretes team agreed to build an experimental bridge using High Performance Concrete. The organizations wanted to demonstrate the feasibility of building a typical prestressed bridge with High Performance Concrete, using means and materials that could be found throughout France. The bridge was built crossing the river Yonne near the town of Joigny, approximately 150 km southeast of Paris. Aesthetical and economical considerations led to the classical design of a balanced continuous three span bridge, which span lengths of 34.00m, 46.00mand 34.00m, a height of 220m and overall width of 15.80m.

The bridge was designed according to the French codes BPEL (Beton Precontraint aux Etats Limites ie. Limit State Design Of Prestressed Concrete) and BAEL (Beton Arme aux Etats Limites i.e.. Limit State Design Of Reinforced concrete). These codes have been upgraded to incorporate 60Mpa concretes since they previously dealt only with concrete strength up to 40Mpa. The use of these codes which include different safety factors, led to an actual maximum compressive strength of 30Mpa in the lower fibre to the central span’s mid sections during the last stages of prestressing.

It should be emphasized that comparison carried out during the preliminary design of the bridge showed that the concrete quantities could be reduced from 1395m³ when using ordinary 35Mpa concrete to 985m³ with 60Mpa high strength concrete. This 30 percent reduction in concrete volume led to a 24 percent load reduction on the pier, abutments and foundations.

Laboratory tests were run to define a mix design allowing the production of ready mix concrete with

· A 28 day mean strength of about 70Mpa.

· The ability to be transported 30km on a boat from the concrete plants and deliver fresh to the construction site

· The ability to be pumped through 120m long pipes.

· A high workability and a sufficient setting time

As the concrete plant was producing concrete fir the bridge, tests were run on every batch. The water cement ratio remained between 0.36 and 0.38.The entrained air contents were within 0.5 and 12 percent. The slumps, measured at the site were 200mm for more than 2 hours. The concrete strength was measured according to French standards using 160mmx320mm test cylinders cast in metallic mould. At 28 days the minimum and maximum strength values were 65.5Mpa and 91.7Mpa. The tensile strength was measured on cylinders where the average tensile strength was 5.1Mpa on 28-day sample.

The first French prestressed concrete bridge designed and built with a 60Mpa characteristic strength and following the French building codes was successfully completed in early 1989.

ADVANTAGES

· Reduction in size of the columns

· Speed of construction

· More economical than steel concrete composite columns

· Workability and pumpability

· Most economical material in terms of time and money

· Increased rentable\useful floor space

· Reduced depth of floor system and decrease in overall building height

· Higher seismic resistance, lower wind sway and drift

· Improved durability in aggressive environment

· Wearing resistance, abrasion resistance

· Durability against chloride attack

· Increased durability in marine environment

· Low shrinkage and high strength

· Service life more than 100 years

· High tensile strength

· Reduced maintenance cost

LIMITATIONS

· High Performance Concrete has to be manufactured and placed much more carefully than normal concrete.

· An extended quality control is required

· In concrete plant and at delivery site, additional tests are required. This increases the cost

· Some special constituents are required which may not be available in the ready mix concrete plants.

FORMWORK

noreply@blogger.com (Civil Engineer) — Thu, 10 Jun 2010 17:40:00 +0530

What is Formwork

Formwork is a die or a mould including all supporting structures, used to shape and support the concrete until it attains sufficient strength to carry its own weight. It should be capable of carrying all imposed dead and live loads apart from its own weight.

INTRODUCTION TO FORMWORK

Formwork has been in use since the beginning of concrete construction.
New materials such as steel, plastics and fiberglass are used in formwork.
greater attention is being given to the design, fabrication, erection and dismantling of formwork

DEFENITION:

As a structure,
Temporary which is designed to contain fresh fluid concrete.
Form it into the required shape and dimensions.
Support it until it cures sufficiently to become self supporting.

The term ‘formwork’ includes the actual material contact with the concrete, known as form face, and all the necessary associated supporting structure.

REQUIREMENTS OF A GOOD FORMWORK SYSTEM

§ How formwork can be erected and de-shuttered fast.

§ How good concrete quality and surface finish can be achieved.

§ What is the optimum stock of formwork required for the size of work force, the specified time schedule and flow of materials.

§ What is the overall cost savings that can be achieved using the right type of formwork.

§ How SAFETY can be improved for the site personnel.

In order to successfully carry out its function, formwork must achieve a balance of following requirements:

Containment
Strength
Resistance To Leakage
Accuracy
Ease Of Handling
Finish And Reuse Potential
Access For Concerted
Economy

Containment: formwork must be capable of shaping and supporting the fluid concrete until it cures.

Strength: formwork must be capable of safely withstanding without distortion or danger the dead weight of the fluid concrete is placed on it, labour weight, equipment weight and any environmental loadings.

Resistance to leakage: all joints in form work must be either close fitting of covered with form tape to make them grout tight. If grout leakage occurs the concrete Will leak at that point. Leakages cause honeycombing of the surface.

Accuracy: formwork must be accurately set out so that the resulting concrete product is in a right place and is of correct shape and dimensions.

Ease of handling: form panels and units should be designed so that their maximum size does not exceed that which can be easily handled by hand or mechanical means. In addition all formwork must also be designed and constructed to include facilities for adjustments, leveling, easing and striking without damage to the form work or concrete.

Finish and reuse potential: the form face material must be selected to be capable of consistently imparting the desired concrete finish (smooth, textured, featured or exposed aggregate etc.) At the same time it should also achieve the required number of reuse.

Access for concrete: any formwork arrangement must be provide access for placing of the concrete. The extent of this provision will be dependent on the ease of carrying out the concrete operations.

Economy: all the formwork is very expensive. On average about 35% of the total cost of any finished concrete unit or element can be attributed to its formwork; of this just over 40% can be taken for material for formwork and 60% for labour. The formwork designer must therefore not only consider the maximum number of times that any form can be reused, but also produce a design that will minimize the time taken for erection and striking.

FORMWORK BASED ON MATERIALS

MATERIALS FOR FORMWORK

Formwork can be made out of a large variety of materials.

The material most commonly being used to date is timber. However, due to the depleting forest reserves and increasing cost of timber the use of alternate materials such as plywood and steel has become prominent.
More recently, materials such as plastics and fiberglass are also being used for pre-fabricating formwork.
The type of material to be used depends on the nature of construction as well as availability and cost of material.
The constraints on the project such as overall cost, time of completion also play a major role in the use of a particular material for formwork.

TIMBER FORMS

Timber is required for practically all jobs of formwork. The timber bring used for formwork must satisfy the following requirements:

It should be durable and treatable
It should have sufficient strength characteristics
It should be light weight and well seasoned without warping,
It should hold nails well.

Advantages of using timber forms:

It is economical for small construction jobs
It is design flexible and easy to erect
It has good thermal insulation which makes it useful to be used in colder

Regions

Iv. It can easily be made into any shape or size

Plywood forms (in combination with timber)

Concrete shuttering plywood is bwp grade plywood, preservative treated and specially suited for use in concrete shuttering and formwork.
The plywood is built up of odd number of layers with grain of adjacent layers perpendicular to each other.
Plywood is used extensively for formwork for concrete, especially for sheathing, decking and form linings.
There are two types of plywood - internal and exterior.
The interior type is bonded with water resistant glue and exterior type is bonded with water proof glue.

Hardboard forms

Hardboard is a board material manufactured of wood fiber, which is then refined or partly refined to form a panel having a density range of approximately 50 to 80 pounds per cubic foot.
Hardboards are standard / non-tempered or tempered.
The tempered one being used for formwork. Tempered hardboard is solid or perforated hardboard panels impregnated with resin under high pressure to make them stronger and more resistant to moisture and abrasion.
The boards available in large sheets have a hard, smooth surface that produces a concrete whose surface is relatively free of blemishes and joint marks.
The thin sheets can be bent to small radii, which is an advantage when casting concrete members with curved surfaces.

ALUMINIUM FORMS

Forms made from aluminum are in many respects similar to those made of steel.
However, because of their lower density, aluminum forms are lighter than steel forms, and this is their primary advantage when compared to steel.
As the strength of aluminum in handling, tension and compression is less than the strength of steel, it is necessary to use large sections.
The formwork turns out to be economical if large numbers of reuses are made in construction.
The major disadvantage of aluminum forms is that no changes can be made once the formwork is fabricated.

PLASTICS

These forms have become increasingly popular for casting unique shapes and patterns being designed in concrete because of the excellent finish obtained requiring minimum or no surface treatment and repairs.

Different types of plastic forms are available like glass reinforced plastic, fiber reinforced plastic and thermoplastics etc.

Fiberglass-reinforced plastic is the most common and has several advantages such as

The material allows greater freedom of design
Unusual textures and designs can be molded into the form
It allows the contractor to pour structural and finished concrete

Simultaneously

Because sections can be joined on the job site in such a way so as to eliminate joints, there is no size limitation

If carefully handled, a number of reuses are possible making it highly

Economical

Vi. It is lightweight and easily stripped

The disadvantage of using plastic forms is that it does not lend itself to field fabrication Hence, the design and planning of this form must be carefully carried out. Also care must take not to damage the plastic by the heat applied for accelerated curing of the concrete. Trough and waffle units in fiberglass are used in construction of large floor areas and multistoried office buildings.

STEEL FORMWORK:

Mostly used in large construction projects or in situations where large number of re-uses of the same shuttering is possible. Suitable for circular or curved shaped structures such as tanks, columns, chimneys. Etc. & for structures like sewer tunnel and retaining wall.

Advantages of steel formwork over timber form:

strong, durable & have longer life
Reuses can be assumed to vary from 100 to 120 wares timber varies from 10 to 12.
Steel can be installed & dismantled with greater ease & speed resulting in saving in labour cost.
Excellent quality of exposed concrete surface obtained. Thus saving in the cost of finishing the conc. surface.
no danger of formwork absorbing water from the conc. & hence minimizing honeycombing

CONSTRUCTION OF FORMWORK:

• propping and centering

• shuttering

• provision of camber

• cleaning & surface treatment

Propping and centering:

The props used for centering may be of steel, timber post or ballies.pillars made up of brick masonry in mud mortar are also sometimes used as props.

Shuttering:

can be made up of timber planks or it may be in the form of panel unit made either by fixing ply wood to timber frames or by welding steel plates to angle framing.

Provision of camber

Certain amount of deflection in structure is unavoidable. It is therefore desirable to give an upward camber in the horizontal member of conc. Structure to counteract the effect of deflection.

Surface treatment

Before laying conc. The formwork should be cleaned of all rubbish particularly the sawdust savings & chippings etc.
Before laying conc. the face of formwork in contact with conc. shall be cleaned & treated with release agent like raw linseed oil or soft soap solution as to prevent the conc. getting struck to the formwork.

Order and method of removing formwork:

Shuttering forming vertical faces of walls, beams & column sides should be removed first. Shuttering forming sofit to slab should be removed next.
Shuttering forming soffit to beams, girders or other heavily loaded member should be removed in the end.

DURATION TAKEN FOR REMOVAL OF FORMWORK

1 WALLS COLUMNS & VERTICAL SIDES

OF BEAMS 1-2 DAY

2 SLABS 3 DAYS

3 BEAM SOFFIT 7 DAYS

4 REMOVAL OF PROPS TO SLABS

A) SLAB SPANNINIG UPTO 4.5M 7 DAYS

B) SLAB SPANNINIG OVER 4.5M 14 DAYS

5 REMOVAL OF PROPS TO BEAMS

AND ARCHES

A) SPANNING UPTO 6 MTS 14 DAYS

B) SPANNING OVER 6 MTS 21 DAYS

TYPES OF FORMWORK

There are different types of formwork available for different purposes. Generally, the formworks for vertical concreting are called wall forms and those for horizontal concreting are called slab or floor forms. The various types of formwork available today in the market are discussed in detail.

TRADITIONAL FORMWORK

This usually consists of standard framed panels tied together over their backs with horizontal members called waling.
The waling is provided with the basic function of resisting the horizontal force of wet concrete.
One side of the wall formwork is first assembled ensuring that it is correctly aligned, plumbed and strutted.
The steel reinforcement cage is then placed and positioned before the other side of the formwork is erected and fixed.
Plywood sheet in combination with timber is the most common material used for wall formwork.
The usual method is to make up wall forms as framed panels with the plywood facing sheet screwed on to studs on a timber frame. This allows for the plywood to be easily removed and reversed and used on both sides so as to increase the number of reuses.
The wall forms are susceptible to edge and corner damage and must be carefully handled.
Special attention must be given to comers and attached piers since the increased pressures applied by wet concrete could cause the abutments to open up, giving rise to unacceptable grout escape and a poor finish to the cast wall.

CLIMBING FORMWORK

Method of casting walls consists of a climbing formwork, the climbing of which may be manual or crane assisted.
It employs a common set of forms used in a repetitive manner for casting walls in set vertical lifts.
After each casting the forms are removed and raised to form the next lift until the required height has been reached.
These forms are widely used in the construction of industrial chimneys, silos, high rise towers & building cores, bridge piers & pylons, airport control towers, telecommunication, towers etc.

The climbing form has many advantages such as the following

Staged construction process allows balance of site resources.
Anchor accessories can be reused after each pour, reducing material costs on current and future construction programs.
In case of trolley mounted formwork, the panel retracts from the face, providing space for cleaning and fixing of concrete.
Formwork & access platforms lifted as one, minimizing crane support, reducing labour and material costs.
fine adjustments of the form face can be made during construction, providing accurate alignment of the form face vertically & laterally.

SLIDING FORMWORK OR SLIPFORMING

slip form means a continuously moving form, moving with such a speed that concrete when exposed has already achieved enough strength to support the vertical pressure from concrete still in the form as well as to withstand lateral pressure caused by wind etc.
Thus, the slip form concreting technique is a rapid and economical construction method that can be applied with great advantage to many types of construction projects such as chimneys, silos, water towers, bridge-columns, lift shaft cores and shaft lining etc.
The technique is based on movable forms which are gradually lifted by hydraulic jacks.
It is a continuous process where wet concrete is added to wet concrete. Reinforcing steel and/or post tensioned cables are continuously fixed as the normal slipping speed is 3 to 6 meters per 24 hours. The slip form construction is designed for each project depending on the structure of the project. The advantages of slip forming are
Minimum consumption of timber and steel plates.
Total elimination of traditional scaffolding
Minimum requirements of carpenters for assembling.
It gives a monolithic structure.
The concrete surfaces can be treated and finished while concrete is green,
Depending on the weather conditions, it is possible to achieve a vertical rise to the tune of 4 to 5 m in summer and 2 to 3 m in winter.
The procedure of continuous slipping is applied to making both inner and outer walls as well as columns of a building.
Form climbs.

PERMANENT FORMWORK

Permanent form or stay-in-place formwork is one in which the form is left as an integral part of the structure.
Permanent formwork can also be utilized as the facing materials of in situ reinforced concrete. They can be of two types—participating and non-participating.
The material used for these forms must be durable and of sufficient strength. Commonly used materials include polyvinyl chloride (pvc), galvanized coiled sheet steel, fabricated steel, carbon/epoxy thin shell.
The high initial cost of design and installation, lack of familiarity for installation and maintenance and more specified form design are some of the barriers to the use of this form.
However, there are various advantages like low cost of transportation and installation, precise form design, maximum flexibility, greater durability with reduced long term maintenance and versatility.

SPECIAL FORMS

These are those forms that are specially designed and manufactured for a particular kind of construction. The need for a special formwork may arise due to several factors such as

• when the contract demands the highest class of dimensional tolerance to be followed

• Where the form work shape required becomes uneconomical or impracticable for site fabrication

• Where the formwork is required to be self-contained i.e. self propelled,

• Where rate of concreting, admixtures or types of concrete are such that concrete pressure developed within forms and stresses in the forms demand special attention where a substantial number of re-uses is envisaged

TABLE FORM

This is a special formwork designed for use in casting large repetitive floor slabs in medium to high-rise structures.
The main objective of reducing the time required re-erecting, striking and re-erecting slab formwork.
A system which can be put as an entire unit, removed, hoisted and repositioned without any dismantling.

GANGED PANEL FORM

The increasing pace in the construction of multi-storey and massive concrete structures, and the parallel progress in development of cranes and other mechanical methods of transporting forms have made the use of ganged prefabricated forms for the concreting of large sections of high walls very common.
Ranging up to 30x50 ft, their size is limited only by the mechanics of handling. Large panels can be assembled flat on the ground where it is easier to work. Delay and lost motion are avoided in stripping because the gang forms are stripped as a unit.

TUNNEL FORM

The tunnel formwork is a room sized structural steel fabricated form which is used to cast the rcc walls and floor slabs of a building as a monolithic structure in a continuous pour. The forms are then heated using hot air blowers for accelerated curing of the concrete. This system is most economical when the structure consists of large number of identical units. There exist two versions of this type of formwork. They are:

A. The half tunnel formwork used to cast only one wall and slab simultaneously

B. The full tunnel formwork used to cast two walls and a slab simultaneously

The sequence of construction involves placing of reinforcement, electrical and sanitary conduits along with the tunnel forms. Concrete is then poured and the open side of the forms is covered and hot air blowers placed inside. The forms are removed the next day and placed on the next site using cranes. The optimum use of tunnel form is in multiunit shear wall structure with identical floor layout at each level.

DOKA FormWork System.

I. Doka System Components

The various basic components that make up the various DOKA system are as follows:

Doka formwork beams
Doka formwork sheets
Dokadur panels
Doka floor props
Form ties and suspension cones
Multi-trip packaging

1. Doka formwork beams

The core of the system lies in the usage of an Engineered timber component, the H-Beam.

The H-beams are manufactured in a modern automated plant at Pondicherry under strict quality control the flanges are made of seasoned chemically treated timber. The web is made of boiling water proof ply wood and joined with the flange by the unique finger jointing method. The H-beams thus manufactured are light, dimensionally stable and retains its structural properties over a period of time even after repeated usage. It is more predictable, easy to design and use, The number of reuses of H-Beams is more than 100 times (8 times that of conventional timber) and it consumes only 40% of timber volume required.

The H-beams are available in two size namely in H-16 - 16 cms depth & H-20 - 20 cms depth, length varying between 1m to 6m.

Salient Feature

• Reduction in consumption of timber.

• Making work at site minimized.

• No. of reuses more than 8 times that of conventional timber.

• Dimensionally stable, uniform in size and consistent in strength.

• Cost ratio per use H-16 beam : conventional timber = 1:3.5

• Economical and long - lasting.

• Light weight @ 6kgs per RMT.

Max. Shear Force	Max. Bending Moment	EI
11 KN	4 KN/M	170 x 106 KG.CM2

Doka beam H20

Innovative end reinforcement .

For less damage to the ends of the beams
For outstanding durability

Outstanding production level.

Ensures uniformly high quality and load-bearing strength for safe and dependable usage
Is the basis for the reliability of the Doka beam formwork and Dokaflex floor formwork
From mechanical strenght grading

Practical marks for all standard lengths.

§ As a grid for easy installation and checking of the Dokaflex 1-2-4 system

Doka beam H20 eco

Ends of beams bevelled for more strength but has no end reinforcement.

2. Doka formwork sheets

Doka has an extensive range of formwork sheets for the most varied areas of application. All sheets are made of glue-bonded layered wood and are extremely strong and dimensionally stable.

Formwork sheet 3-S Plus

Three-ply concrete-formwork sheet, made of European spruce (picea abies), designed specially for building. Produces a uniform concrete surface.

 Surface: Synthetic melamine resin glue with PU sealant and light corundum sanding on one side

 Bonding: Boilproof and weatherproof

 Edges: Impregnating emulsion,
Doka yellow

 Thicknesses: 21 and 27 mm

Formwork sheet 3-SO

Three-ply concrete-formwork sheet, made of European spruce. Produces a uniform concrete surface.

§ Surface: Synthetic melamine resin glue

§ Bonding: Boilproof and weatherproof

§ Edges: Impregnating emulsion,

§ Doka yellow

§ Thicknesses: 21 and 27 mm

Dokaplex Multi-ply sheets

High-grade multi-ply sheet made of Finnish birch hardwood for use again and again. Produces a high-quality, smooth concrete surface.

Surface: Phenol-resin coating, 120 g/m²
Bonding: Boilproof and weatherproof phenol-resin glue (BFU 100) to DIN 68705-T3
Edges: Dispersion
Thickness: 21 mm

3. Dokadur panels

Dokadur panels are the state of the art for floor-slab panels. All-round edge and surface sealing dependably protects the panel against the wear and tear of everyday construction work.

Maximised number of reuses and best-quality concrete surfaces.

From special surface sealing by means of PUR varnish and melamine resin coating with precision-metered corundum sanding
For improved safety at work, because risk of slipping is reduced
From significantly reduced moisture absorption for much-reduced discolouration, structuring and cracking

Big savings on costs

From easy cleaning of the surfaces, ready for the next use
From all-round edge protection made of high-grade PU
For exact edges with minimal cleaning
For low costs on account of easy and fast reconditioning of the edge

4. Doka Floor Props.

Doka floor props are the right choice for every application. High load-bearing strength plus many practical details that help to make handling easier.

The props are available in various sizes viz. CT-250,CT-300,CT-340 & CT-410. The number indicates the extended length of props in cms.

Carrying capacity is rated from 20 kN to 30 kN.

The tripods make the props self standing for easier and faster erection of the shuttering system. The adjustments in height are obtained by operating the prop nut. The required dimension in plan is obtained by side-lapping of the H-Beams in the primary or secondary layer.

A very accurate and convenient shutter is ready for tying of reinforcement and concreting.

The system also facilitates re-propping. By adopting the method of repropping it is possible to reduce the total quantity of formwork materials significantly. The system is very well adapted for use alongwith the L&T-Doka Beam Forming Supporting system.

5. Form ties and suspension cones

Doka has a complete range of tried-and-tested formtie solutions and dependable suspension points for wall formwork, single-sided formwork and climbing formwork in uncompromising quality for maximum safety.

Doka tie rods and anchor accessories

§ Provide safety through superb manufacturing quality

§ Reduce labour costs for installing ties, because a hammer is all that is needed for easy installation

§ Are durable, robust and unaffected by dirt

Robustly dimensioned universal climbing cones

§ ensure firm connections between structure and formwork

§ for safety on high structures

§ for all kinds of climbing formwork

Safe suspension solutions for working and protection platforms

§ With different attachments to suit the application

§ Ideally matched to the carrying capacity of Doka working and protection platforms

§ Easy to install and reusable.

6. Multi-trip packaging

Multi-trip packaging such as containers, stacking pallets and skeleton transport boxes keep everything in place on the site, minimise time wasted searching for parts, and streamline the storage and transport of system components, small items and accessories.

Savings on material overheads and labour costs.

Through faster loading and unloading of system components, small items and accessories
Through easy relocation to the next point where the parts are needed
Through safe storage in stacks, particularly when space is at a premium

Stacking pallets 150 and 120 simplify the storage and transport of floor props, removable folding tripods, formwork beams and Dokadur panels. The clamp-on wheels make the stacking pallets mobile, so they can easily be steered through standard door-size openings in residential accommodation projects.

II. DOKA Floor System

No matter what the room height, the shape of the layout or the slab thickness, with Doka you always have exactly co-ordinated formwork in one single consistent system, comprising a conveniently small number of easy to manage system components.

Dokaflex 1-2-4

Dokaflex 1-2-4 is the fast, versatile floor formwork for floorplans of any shape, for beams, slab overhangs and semifinished floor elements – and the ready reckoner is ideal for calculating the quantities of materials, so there's no need for formwork planning. The free choice of formwork sheets leaves nothing to be desired when it comes to the finished structure of the fair-face concrete.

The L&T-Doka Fex system is suitable for RC-floors upto 4.40 m high.

The plywood sheathing is supported by a layer of secondary H-Beams at the designed spacing. The primary layer of H-Beams are supported with necessary accessories over the collapsible telescopic props fitted with tripods to ensure lateral stability.

Defined positioning grid with full flexibility in floorplan geometry

For quick erection of the formwork, because the positioning points are clear
Enables rapid adaptation to walls and columns by simply telescoping the transverse and longitudinal beams

Speedy progress and simple logistics

Because there is only a small number of matched individual components
With high-grade Eurex floor props with consecutively numbered pegging holes and low release forces
With high-grade Eurex floor props with consecutively numbered pegging holes and low release forces
Because the ready reckoner makes it easy to calculate the quantities needed
Because dispensing with planning and preparatory operations cuts costs by a significant margin
Because the maximum pitches for longitudinal and transverse beams and props are marked on the beams - for floor-slab thicknesses up to 30 cm

Safety and economy

From durable and robust individual components
Because the panels can be rented
With high-grade polyurethane surround for first-class concrete surfaces and reduced investment costs
With non-slip surfaces for significantly enhanced safety at work
With high-grade Eurex floor props with consecutively numbered pegging holes and low release forces
With the new, much-improved longitudinal and transverse beams for significantly reduced post-use costs

Every requirement for fair-faced concrete fulfilled

By free choice of formwork sheets
By the sealed surface of the rentable panels

Dokamatic table

The innovative design of the Dokamatic table makes for even faster formwork handling whenever large floor slabs have to be cast. Standard functional components can be installed for straightforward, speedy adaptation to changing requirements on the construction site.

Fast repositioning reduces labour costs

Because fully assembled units are manoeuvred quickly into place - no laborious carrying of individual components from one location to the next
Because practical shifting devices makes for virtually fatigue-free operations
Because easier to handle and safer than hand-operated formwork, particularly as room heights increase

The Dokamatic table helps save on labour and on crane time: One man using the shifting trolley with attachable drive unit can move the tables to the next casting location on the same level. The system is optimised for minimal forming times on large-area projects and deals easily with varying requirements in terms of statics and geometry.

Dokamatic table sizes

Comes in 4 rentable standard sizes with grid logic: 4.0 x 2.0 m, 4.0 x 2.5 m, 5.0 x 2.0 m and 5.0 x 2.5 m
Special sizes for special applications can be supplied at any time
Made up of high-grade system components such as the sturdy Dokamatic table waling 12 and Doka beams H20 top for outstanding durability and minimum post-use costs
Fully assembled Dokamatic tables delivered to your site right on time

Load-bearing tower Staxo

Staxo is a high-strength load-bearing tower made of robust steel frames for high shoring and heavy loads. Integrated connectors for rapid assembly. This modern load-bearing tower system comprises only a few individual parts and is extremely versatile. A comprehensive range of safety accessories completes the system.

Highly stable and highly versatile

§ With 1.52 m wide frame with non-buckling vertical sections

§ With 50 cm grid for setting the frame spacing

§ With the tower unit's large footprint

§ Because horizontal loads are safely dissipated

§ Load-bearing capacity up to 70 kN/leg

Speedy assembly, even when the towers are high

§ Because there are only a few individual parts, they are light and easy to handle

§ Because the vertical adapters for the next lift are integrated, without loose parts or add-ons

§ With drop-in assembly battens and integrated climbing rungs

Less crane time needed

§ Because the towers can be pre-assembled on the flat, then hoisted into position

§ With shifting carriages for horizontal repositioning

Staxo frame

Extremely strong, galvanised steel frame for straightforward height adjustment in a 30 cm grid; choice of three heights 0.90, 1.20 and 1.80 m
Frame spacing with diagonal crosses from 1.00 to 2.50 m adjustable in 50 cm grid
Reliably withstands horizontal forces such as wind loads
Integrated next-lift frame adapters for ergonomic handling even high above the ground - no tools required
Integrated climbing rungs and drop-in assembly battens support safe assembly and disassembly

Diagonal cross

Timesaving integration of horizontal and diagonal braces in a single component
Different lengths for variable frame spacing
Colour clips and stamping for clear marking of the lengths
Safe assembly with captive gravity catches

Setting the next lift is always quick and safe: no time is lost looking for parts, because the locking springs (1),

(3) and connecting sleeves (2) are captive, integrated into the frames.

No additional parts or loose parts, so even high above the ground handling is still straightforward.

Height adjustment

Height adjustment accurate to the millimetre, even under load. By means of screw-jack U-spindle at the top, screw-jack foot or heavy-duty screw jack at the bottom. The heavy-duty screw jack 130 has an extension height of 130 cm and is available for jobs requiring maximum versatility.

Beam forming support system

The L&T-Doka Beam Forming Support system is suitable for RC-Beams of depth between 30 cm to 120 cm.

Beam bottom

The plywood sheathing is supported by a layer of secondary H-20 Beams at the designed spacing to form the beam bottom. The primary H-Beams in turn support the secondary layer.

Beam sides

The plywood sheathing is supported by H-Beams at the designed spacing running along the length of the RC-beam to form the beam sides. The H-beams are supported by the beam forming support which are clamped onto the H-20 beams provided for the Beam bottom. The beam forming support ensures the right angle between the beam bottom and sides. The BFS extn. provides the necessary adjustment in depth.

The beam forming support with extension are available in three sizes viz.BFS with extn.600mm long, 900mm long & 1200mm long.

III. Wall Formwork System

The L&T-Doka Wall formwork system is suitable for casting of RC-Walls including water tight structures.

The plywood sheathing is supported by H-Beams which are in turn supported by the steel walers. The wall formwork facilitates fixing of working platforms for access, checking of reinforcement, concreting etc., the panels also have provision for fixing for alignment system which ensure verticality. The pressure due to concrete are sustained by High strength tie system.

The walers are available in sizes of 0.8m, 1.2m, 1.6m, 1.8m, 2m & 2.4m the inside corners are formed by “universal inside corner” and the outside by universal outside fixing or angle plates. The high strength tie system can be through tie system or lost anchor system depending on the structure. The H-Beams can be butt jointed to form larger size of panels.

The formwork panel along with the working platform and alignment systems can be lifted as a single unit using a crane thus the labour involved in each operation of erection and deshuttering is reduced to a minimum. The panels are formed in the carpentry workshop at site and the number of operations/assembly of components at each location is minimal and hence accuracy is maintained. Since large panels are handled as a single unit, the damage/loss of small components is eliminated contributing to very high material productivity. In the absence of a crane the panels can be dismantled and handled separately. The wall formwork system can handle very large pressures generated due to pumping of concrete.

The planners place the Doka formwork beams H 20 (1) and the bracing, which consists of steel waling (2) to suit the anticipated load. The sheeting (3) is freely selectable – your choice of smooth fair-faced concrete, wood-textured surface, and so on.

Doka framed formwork Frameco

The Frameco formwork system

Forms wall heights up to 3.00 m without stacking
Has sturdy, galvanised steel frames to produce smooth concrete surfaces
Permissible fresh-concrete pressure 70 kN/m²

Only 2 anchors up to a height of 3.00 m

Means fewer anchors have to be set, so forming work is faster
Reduces labour costs for post-casting work on the anchorage holes

End-to-end 15 cm grid with only 5 panel widths

Simplifies planning, forming and logistics on the construction site
Reduces the number of cost-intensive closures
Means matching panel formats for best possible utilisation of formwork
Reduces quantities in stock and costs for rental, because of effortless adaptation to any floor plan

§ Makes for compact lifting units for fast positioning and short crane times
IV. Column Formwork System

The L&T-Doka Column formwork system is suitable for casting of columns of minimum 15cm * 15cm .

In the Column formwork system the H-Beams along with steel walers and accessories makeup the assembly. The Column formwork facilitates fixing of working platforms for access, checking of reinforcement, concreting etc., The formwork panel along with the working platform and alignment systems can be lifted as a single unit using a crane thus the labour involved in each operation of erection and deshuttering is reduced to a minimum. The panels are formed in the carpentry workshop at site and the number of operations/assembly of components at each location is minimal and hence accuracy is maintained. Since large panels are handled as a single unit, the damage/loss of small components is eliminated contributing to very high material productivity. In the absence of a crane the panels can be dismantled and handled separately. The column formwork system can handle very large pressures generated due to pumping of concrete.

Any column size, straight from the modular system ...

For speedy forming of any column cross-section with standard parts
For optimum adaptation to any special geometry up to 5 m in diameter
For column cross-sections up to 120 x 120 cm with only one splice plate
For first-class concrete surfaces with any sheeting
Permissible fresh-concrete pressure 90 kN/m²

Some of the possible cross-sections of column

V. Climbing Formwork System

The L&T-Doka Climbing System are used for tall structures like cooling towers, etc where it is very uneconomical to provide staging or scaffolding for supporting the external or internal wall formwork.

In this system a bracket is hooked on to anchors called lost anchors provided in the already cast wall and supports/alignments are taken from these brackets. The brackets are suitably braced to prevent any sway and are provided with walkways/working platforms / handrails etc for safety and ease of working.

Varying degrees of sophistication are available in the

Climbing formwork systems, a few of which are as listed.

CB - 150 A - Simple Climbing, Crane handled - platform width 1.50 m. The brackets & wall formwork are to be handled separately.

CB - 150 F- Traveling Climbing, Crane handled - platform width 1.50 m. roll back arrangement for deshuttering & cleaning of shutters. The wall formwork and climbing bracket are lifted as one unit.

Automatic climbing formwork, the wall formwork along with the climbing brackets slide along the wall using motors, thus eliminating the need for crane. This system is very often used for natural draught cooling towers.

MF - 240 - Simple Climbing, Crane handled - platform width 2.40 m. these brackets can also be fitted with automatic climbers SKE-50 which is a hydraulic system with 5T carrying capacity or SKE-100 with 10T carrying capacity.

The MF 240 system

* Travelling unit MF (1):

Platform is 2.40 m wide for safe and convenient manipulation of the formwork. 75 cm retraction for easy cleaning of the formwork and for working on the reinforcement.

* Climbing bracket MF (2):

Combines with beam and frame formwork, high load-bearing capacity (50 kN per climbing bracket), angle of inclination ± 15° from vertical.

* Working brackets (2):

Modular principle for versatility: these brackets can be used as pouring, intermediate and suspension brackets.

The SKE system

The modular system for automatic climbing

* Free positioning of brackets and automatic climbers as single-section climbing scaffold

* Lift heights up to 5.50 m

* Formwork systems:

• wall formwork FF 20 and large-area formwork Top 50

• framed formwork Framax and Alu-Framax

* Climbing speed 5 min/m

SKE 50

* Load-carrying capacity 5 metric tons per bracket

* Ideal solution for a huge number of climbing tasks

* Up to 40 automatic climbers per hydraulic unit

SKE 100

* Load-carrying capacity 10 metric tons per bracket

* Platform system for simultaneous work at different levels

* Extremely strong brackets permit wide, variable spacing

FLY ASH

noreply@blogger.com (Civil Engineer) — Thu, 10 Jun 2010 17:07:00 +0530

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Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by flue gases and collected by electrostatic precipitation. Fly ash is most used pozzolanic material all over the world.

In recent time, the importance and use of fly ash has grown so much that it has almost become a common ingredient in concrete, particularly in making high strength and high performance concrete. The use of fly ash as concrete admixture not only extends technical advantages but also contributes to the environmental pollution control. Extensive research is being carried out in most part of the world that could be accrued in the utilization of fly ash, which is basically a waste product.

The volume of fly ash produced is about 75 million tons per year, the disposal of which has become a major concern. Only about 5% of the total fly ash is utilized in India the remaining of which has to be disposed. Instead of doing so, it can be utilized in a major way. The role of it plays in the field of concrete technology. In this discussion it would be interesting to discuss on fly ash from the point of concrete making.

There are two ways that the fly ash can be used: one way is to intergrind certain percentage of fly ash with cement clinker at the factory to produce Portland pozzolona cement (PPC) and the second way is to use the fly ash as an admixture at the time of mixing the concrete at the site of work. But the main problem is that the fly ash produced in the 75 thermal power plants in India is not of the similar characteristics. The suitability of fly ash used in the making of the concrete has to be further processed. The quality of fly ash should be of the standard of IS: 3812-1981. For better utilization of fly ash it becomes important to know the hydration reactions, pozzolanic activity evaluation, effect of fly ash on fresh and hardened concrete, durability etc.

2. Scope of the study of fly ash characteristics:

The importance of fly ash cannot be exaggerated. It is no longer a cheap substitute for cement, nor an extender or an addition to the mix. Fly ash bestows important advantages upon concrete, and it is, therefore, essential to understand the role and influence of fly ash. The variability of the properties of fly ash arises from the fact that fly ash is not a specially manufactured product and cannot, therefore, be governed by strict requirements of a standard. The power station which produces fly ash varies its operation in response to the power demand. The variation in the fly ash are those in glass content, carbon content, particle shape and size distribution, as well as in the presence of magnesia and other minerals, and even in colour. It is possible to improve the size distribution of fly ash particles by classification and by grinding.

As said earlier the fly ash is an artificial pozzolan and it exhibits different characteristics with different compounds of cement. The cement might contain different compositions of the above said Tri calcium silicate, Di calcium silicate, tri calcium aluminate etc. hence it becomes necessary to study the reactions exhibited by the fly ash with each of these compounds so that the necessary concrete can be obtained. Hence the cement should match with the fly ash at the first instance. This becomes important because it might have an affect on the strength and durability of the concrete.

3. Types of fly ash as per ASTM

ASTM broadly classify fly ash into two classes.

Class F: Fly ash normally produced by burning anthracite or bituminous coal, usually has less than 5% CaO. Class F fly ash has pozzolanic properties only.

Class C: Fly ash normally produced by burning lignite or sub-bituminous coal. Some class C fly ash may have CaO content in excess of 10%. In addition to pozzolanic properties, class C fly ash also possesses cementitious properties.

4. Hydration reactions:

4.1:Hydration of Portland cement:

The setting and hardening of Portland cement occur as a result of the reaction between the compounds of cement and water. The major compounds of cement that produce reaction products and the products are shown in the equation below.

2C₃S + 6H C₃S₂H₃ + 3CH

Tri calcium silicate

2C₂S + 4H C₃S₂H₃ + CH

Di calcium silicate

C₃A + 3CSH₂+ 26H C₃A (C’S)₃H₃₂ C₃AC’SH₁₂

Tri calcium gypsum ettringite monosulphoaluminate

Aluminate hydrate

4.2:The fly ash hydration reactions:

High calcium fly ash, which contains mainly of glass phase and some crystalline phases, has self-hardening properties. Ettringite, monosulphoaluminate hydrate, and C-S-H cause hydration of fly ash when mixed with water.

Low calcium fly ash, which has very little or no self-cementatious properties, hydrates when alkalis and Ca (OH)₂ are added. As more Ca (OH)₂ is supplied, more of it is fixed by silica and alumina in fly ash. The degree of hydration of fly ash is also increased in the presence of gypsum.

4.3.The effect of fly ash on the hydration of cement compounds:

The fly ash reaction with that of C₂S, C₃A AND C₃S is more complicated. According to V.N.Malhotra (proffesor, CANMET, Natural resources, Canada) the schematic explanation of fly ash and its reaction with C₃S is given below:

“In C₃S pozzolan system, calcium ions dissolved from C₃S run about freely in liquid and rare absorbed on the surface of pozzolan particles. C-S-H formed by the hydration of C₃S precipitates as the hydrates of high Ca/Si ratio on the surface of C₃S grains and as the porous hydrates of low Ca/Si ratio on the surface of pozzolan particles. Attack of the pozzolan surface in water brings about gradual dissolution of Na⁺ and K⁺, resulting in Si and Al rich amorphous layer on the surfaces. Dissolved Na⁺ and K⁺ increase the OH- concentration and accelerate the dissolution of SiO₄^4- combine with Ca²⁺ to increase the thickness of the layer. Due to the osmotic pressure, the layer swells gradually and the void between the layer and pozzolan particle is formed. When the pressure in the void ruptures the film, SiO₄^4- and AlO^2- diffuse into the Ca^± rich solution. Additional C-S-H and Ca-Al hydrate precipitate on the surface of outer hydrates of C₃S particles and to slight extent on the ruptured film. Vacanted film, vacant spaces remains inside the film as the hydrates do not precipitate there because of high concentration of alkalis. For pozzolan with low alkalis, destruction of amorphous Si, Al rich film enables Ca²⁺ to move into the inside of the film and precipitate calcium silicate and calcium aluminate hydrates on the surface of pozzolan grain. There fore no space is observed between pozzolan grains and hydrates.”

It was observed that the degree of hydration of C₃S alone after one day was 35%, while that of the mixture with fly ash was 45% (ACC designers manual-2003 &XRD). This result obviously shows that adding fly ash accelerates the hydration of C₃S.

Many investigations have shown that fly ash retards the hydration of C₃A. The degree of this retardation mainly depends on the Sulphate content of fly ash, the amount of dissolved alkalis, and the calcium absorption capacity. Ca²⁺and SO₄^2-are dissolved from high calcium fly ashes. Dissolved ca²⁺ is absorbed on to the Al rich surface (produced by non-stoichiometric dissolution) lowering the hydration activity. Further more, the absorption of SO₄^2- also retards the hydration of C₃A. Sulphate in fly ash retards the hydration more than the equivalent amount of added gypsum. . The schematic explanation of the mechanism of hydration in the C₃A- pozzolona system: The early reactions of the fly ash-cement system was described by diamond et al. He explained the occurrence of so-called duplex films, which rapidly develop in hydrating cement compounds around exposed surfaces, such as sand grains and coarse aggregates. He also described about the formation of uniform continues layer of calcium hydroxide and a thin layer of less widely spread C-S-H gel. The gel is usually formed roughly perpendicular to the calcium hydroxide layer. The duplex is formed usually after one day when kept at room temperature.

5. Physical and Chemical requirements as per IS: 3812-1981:

Table 1: Physical requirements

Sl no	Characteristic	Requirement Grade of fly ash
Sl no	Characteristic	I	II
1	Fineness- specific surface in m2/kg by Blaine’s permeability method, Min	320	250
2	Lime reactivity- Average compressive strength in N/mm², Min	4.0	3.0
3	Compressive strength at 28 days N/mm², Min	Not less than 80% of the strength of corresponding plain cement mortar cubes
4	Dry shrinkage, %, Max	0.15	0.10
5	Soundness by autoclave test expansion of specimen, %, Max	0.8	0.8

Table 2: Chemical requirements

Sl no.	Characteristic by mass	Requirement
1	SiO₂ + Al₂O₃ + Fe₂O₃, Min	70.0
2	SiO₂, Min	35.0
3	MgO, Max	5.0
4	SO₃, Max	2.75
5	Na₂O (refer Note 1) Max	1.5
6	Loss on ignition, Max	12.0
Note 1: Applicable only when reactive aggregates are used in concrete and only if the purchaser specially requests for.

6. Engineering properties

Some of the engineering properties of fly ash that are of particular interest when fly ash is used as an admixture or a cement addition to PCC mixes include fineness, LOI, chemical composition, moisture content, and pozzolanic activity. Most specifying agencies refer to ASTM C618 when citing acceptance criteria for the use of fly ash in concrete.

6.1 Fineness: Fineness is the primary physical characteristic of fly ash that relates to pozzolanic activity. As the fineness increases, the pozzolanic activity can be expected to increase. Current specifications include a requirement for the maximum allowable percentage retained on a 0.045 mm (No. 325) sieve when wet sieved. ASTM C618 specifies a maximum of 34 percent retained on a 0.045 mm (No. 325) sieve. Fineness can also be assessed by methods that estimate specific surface area, such as the Blaine air permeability test commonly used for Portland cement.

6.2 Pozzolanic Activity (Chemical Composition and Mineralogy):Pozzolanic activity refers to the ability of the silica and alumina components of fly ash to react with available calcium and/or magnesium from the hydration products of Portland cement. ASTM C618 requires that the pozzolanic activity index with Portland cement, as determined in accordance with ASTM C311 be a minimum of 75 percent of the average 28-day compressive strength of control mixes made with Portland cement.

6.3 Loss on Ignition: Many state transportation departments specify a maximum LOI value that does not exceed 3 or 4 percent, even though the ASTM criteria is a maximum LOI content of 6 percent. This is because carbon contents (reflected by LOI) higher than 3 to 4 percent have an adverse effect on air entrainment.

Fly ashes must have a low enough LOI (usually less than 3.0 percent) to satisfy ready-mix concrete producers, who are concerned about product quality and the control of air-entraining admixtures. Furthermore, consistent LOI values are almost as important as low LOI values to ready-mix producers, who are most concerned with consistent and predictable quality.

6.4 Moisture Content: ASTM C618 specifies a maximum allowable moisture content of 3.0 percent.

Some of the properties of fly ash-concrete mixes that are of particular interest include mix workability, time of setting, bleeding, pumpability, strength development, heat of hydration, permeability, resistance to freeze-thaw, sulfate resistance, and alkali-silica reactivity.

6.5 Workability: At a given water-cement ratio, the spherical shape of most fly ash particles permits greater workability than with conventional concrete mixes. When fly ash is used, the absolute volume of cement plus fly ash usually exceeds that of cement in conventional concrete mixes. The increased ratio of solids volume to water volume produces a paste with improved plasticity and more cohesiveness.

6.6 Time of Setting: When replacing up to 25 percent of the Portland cement in concrete, all Class F fly ashes and most Class C fly ashes increase the time of setting. However, some Class C fly ashes may have little effect on, or possibly even decrease, the time of setting. Delays in setting time will probably be more pronounced, compared with conventional concrete mixes, during the cooler or colder months.

6.7 Bleeding: Bleeding is usually reduced because of the greater volume of fines and lower required water content for a given degree of workability.

6.8 Pumpability: Pumpability is increased by the same characteristics affecting workability, specifically, the lubricating effect of the spherical fly ash particles and the increased ratio of solids to liquid that makes the concrete less prone to segregation.

6.9 Strength Development: Previous studies of fly ash concrete mixes have generally confirmed that most mixes that contain Class F fly ash that replaces Portland cement at a 1:1 (equal weight) ratio gain compressive strength, as well as tensile strength, more slowly than conventional concrete mixes for up to as long as 60 to 90 days. Beyond 60 to 90 days, Class F fly ash concrete mixes will ultimately exceed the strength of conventional PCC mixes. For mixes with replacement ratios from 1.1 to 1.5:1 by weight of Class F fly ash to the Portland cement that is being replaced, 28-day strength development is approximately equal to that of conventional concrete.

Class C fly ashes often exhibit a higher rate of reaction at early ages than Class F fly ashes. Some Class C fly ashes are as effective as Portland cement in developing 28-day strength. Both Class F and Class C fly ashes are beneficial in the production of high-strength concrete. However, the American Concrete Institute (ACI) recommends that Class F fly ash replace from 15 to 25 percent of the Portland cement and Class C fly ash replace from 20 to 35 percent.

6.10 Heat of Hydration: The initial impetus for using fly ash in concrete stemmed from the fact that the more slowly reacting fly ash generates less heat per unit of time than the hydration of the faster reacting Portland cement. Thus, the temperature rise in large masses of concrete (such as dams) can be significantly reduced if fly ash is substituted for cement, since more of the heat can be dissipated as it develops. Not only is the risk of thermal cracking reduced, but greater ultimate strength is attained in concrete with fly ash because of the pozzolanic reaction. Class F fly ashes are generally more effective than Class C fly ashes in reducing the heat of hydration.

6.11 Permeability: Fly ash reacting with available lime and alkalies generates additional cementitious compounds that act to block bleed channels, filling pore space and reducing the permeability of the hardened concrete. The pozzolanic reaction consumes calcium hydroxide (Ca(OH)₂), which is leachable, replacing it with insoluble calcium silicate hydrates (CSH). The increased volume of fines and reduced water content also play a role.

6.12 Resistance to Freeze-Thaw: As with all concretes, the resistance of fly ash concrete to damage from freezing and thawing depends on the adequacy of the air void system, as well as other factors, such as strength development, climate, and the use of deicer salts. Special attention must be given to attaining the proper amount of entrained air and air void distribution. Once fly ash concrete has developed adequate strength, no significant differences in concrete durability have usually been observed. There should be no more tendency for fly ash concrete to scale in freezing and thawing exposures than conventional concrete, provided the fly ash concrete has achieved its design strength and has the proper air void system.

6.13 Sulfate Resistance: Class F fly ash will generally improve the sulfate resistance of any concrete mixture in which it is included. Some Class C fly ashes may improve sulfate resistance, while others may actually reduce sulfate resistance and accelerate deterioration. Class C fly ashes should be individually tested before use in a sulfate environment. The relative resistance of fly ash to sulfate deterioration is reportedly a function of the ratio of calcium oxide to iron oxide.

6.14 Alkali-Silica Reactivity: Class F fly ash has been effective in inhibiting or reducing expansive reactions resulting from the alkali-silica reaction. In theory, the reaction between the very small particles of amorphous silica glass in the fly ash and the alkalis in the Portland cement, as well as the fly ash, ties up the alkalis in a nonexpansive calcium-alkali-silica gel, preventing them from reacting with silica in aggregates, which can result in expansive reactions. However, because some fly ashes (including some

Class C fly ashes) may have appreciable amounts of soluble alkalis, it is necessary to test materials to be used in the field to ensure that expansion due to alkali-silica reactivity will be reduced to safe levels.

Fly ash, especially Class F fly ash, is effective in three ways in substantially reducing alkali-silica expansion:

1) It produces a denser, less permeable concrete;

2) When used as a cement replacement it reduces total alkali content by reducing the Portland cement; and

3) Alkalis react with fly ash instead of reactive silica aggregates.

Class F fly ashes are probably more effective than Class C fly ashes because of their higher silica content, which can react with alkalis. Users of Class C fly ash are cautioned to carefully evaluate the long-term volume stability of concrete mixes in the laboratory prior to field use, with ASTM C441 as a suggested method of test

7. Fly ash in the production of high performance concrete:

HPC is usually produced using high quality materials. These constituents drastically increase the initial cost of HPC, thus hindering its more widespread usage. But the research done by university of Minho shows that Using low quality as received materials like fly ash and locally available crushed aggregates low cost HPC can be produced. The effect of the amount of fly ash was evaluated using 0%, 20%, 40% and 60 % of cement, replacing fly ash. Workability, mechanical and durability properties aspects were also studied. The results obtained indicated that it is possible to produce HPC with up to 60Mpa by replacing 40% of cement by fly ash. Hence it is possible to conclude that the use of fly ash is beneficial, in terms of durability, workability, etc., when there is a compromise for the late development of the strength. For more information in the development of HPC using fly ash can be obtained from University of Minho, Department of Civil Engineering, Portugal.

8. Utilization of fly ash:

Keeping in view this versatility of fly ash, several agencies - (govt. private, public sector, NGOs) are involved in fly ash utilization and safe disposal efforts in India. These include Ministry of Environment & forests, Ministry of Urban Development, Department of Science & Technology, National Thermal Power Corporation, CSIR Laboratories, Engineering Institutes, IITs, State Electricity Boards, etc.

Areas of Fly Ash Utilization

· Fly Ash Bricks

· Embankment and Fills

· Road Pavement

· Portland Pozzolona Cement

· Cement Concrete and Mortar

· Light Weight Aggregates

· Back filling of Open Cast Mine

· Stowing of Under Ground Mines

· Agriculture

· Manufacture of Alum, Paint, Ceramic, Asbestos Cement Products.

9. Cases where fly ash has been used:

Table: Fly ash utilization in Mass concrete or Dam construction

Sl. No	Structures	State	Cement replaced (%)	Source of fly ash
1.	Gurgoan tunnel	Haryana	15	Delhi
2.	Jawar sagar Dam	Rajasthan	20	Delhi
3.	Kakki Dam	Kerala	20	Neyveli
4.	Navora barrage	U.P.	15	Harduaganj
5.	Rihad Dam	U.P.	15	Bokaro
6.	Sone Barrage	Bihar	15	Bokaro
7.	Umium Project	Assam	Not available	Durgapur
8.	Chandil dam	Bihar	25	Talcher

Table: Fly ash Experimental Housing Schemes By National Buildings Organisation

Location	Application
Hindustan Prefab Ltd. Staff Quarters, New Delhi	15% replacement of fly ash in precast RCC components.
Government double storied staff quarters R.K.Puram at New Delhi	20% fly ash in cement and mortar
4 storied Government quarters at dhaulakuan New Delhi	20% fly ash in cement and mortar
Double storied building at the S.E.R.C.Chennai.	Precast reinforced channel units
Dwelling units at Pankha road, New Delhi	Foundation, Concrete mortar flooring plaster some RCC items
Flats at Besant Nagar, Chennai	Cement mixture

10. Benefits of Using Fly Ash

Concrete in its hardened state — with fly ash — shows improved performance:

Greater strength. Fly ash increases in strength over time, continuing to combine with free lime.
Decreased permeability. Increased density and long-term pozzolanic action of fly ash, which ties up free lime, results in fewer bleed channels and decreases permeability.
Increased durability. The lower permeability of concrete with fly ash also helps keep aggressive compounds on the surface, where destructive action is lessened. Fly ash concrete is also more resistant to attack by sulfate, mild acid, and soft (lime hungry) water.
Reduced alkali silica reactivity. Fly ash combines with alkalis from cement that might otherwise combine with silica from aggregates, thereby preventing destructive expansion.
Reduced heat of hydration. The pozzolanic reaction between fly ash and lime generates less heat, resulting in reduced thermal cracking when fly ash is used to replace a percentage of Portland Cement.
Reduced efflorescence. Fly ash chemically binds free lime and salts that can create efflorescence. The lower permeability of concrete with fly ash can help to hold efflorescence-producing compounds inside the concrete.

The ball-bearing effect of fly ash in concrete creates a lubricating action when concrete is in its plastic state. This means enhanced concrete workability:

Increased workability. Concrete is easier to place with less effort, responding better to vibration to fill forms more completely.
Increased ease of pumping. Pumping requires less energy; longer pumping distances are possible.
Improved finishing. Sharp, clear architectural definition is easier to achieve, with less worry about in-place integrity.
Reduced bleeding. Fewer bleed channels decreases porosity and chemical attack. Bleed streaking is reduced for architectural finishes. Improved paste to aggregate contact results in enhanced bond strengths.
Reduced segregation. Improved cohesiveness of fly ash concrete reduces segregation that can lead to rock pockets.
Reduced slump loss. More dependable concrete allows for greater working time, especially in hot weather.

EARTHQUAKE RESISTANT CONSTRUCTION

noreply@blogger.com (Civil Engineer) — Wed, 9 Jun 2010 22:34:00 +0530

Earthquake is a natural phenomenon occuring with all uncertanities. Engineering design aims to link economics, social, environmental and safety factor to produce the best solution. India is a large country. Nearly two thirds of its area is earthquake prone. A large part of rural and urban buildings are low-rise buildings of one two three stroyes. Many of them may not be adequately designed from engineers trained in earthquake engineering. Most loss of life and property due to earthquakes occur due to collapse of buildings. The number of dwelling units and other related small-scale constructions might double in the next two decades in India and other developing countries of the world. This amplifies the need for a simple engineering approach to make such buildings earthquake resistant at a reasonably low cost.

The behaviour of a building during earthquakes depend critically on its overall shape, size and geometry, in addition to how the earthquake forces are carried to the ground. Hence, at the planning stage itself, architects and structural engineers must work together to ensure that the unfavourable features are avoided and a good building configuration is chosen. The main objective of seismic resistant construction is that the structure does not collapse during mild earthquakes. This also helps in preventing catastrophic failure of the suructure giving sufficient warning during severe earthquakes thereby saving precious lives.

In this presentation emphasis will be given to the performance of unengineered buildings during earthquake and some methods to reduce the damages during earthquake.

EARTHQUAKE RESISTANT CONSTRUCTION

INTRODUCTION

Earthquake is a natural phenomenon occurring with all uncertainties. Among all the natural calamities, the most devastating one is earthquake. During the earthquake, ground motions occur in a random fashion, both horizontally and vertically, in all directions radiating from epicenter. These ground motions cause structures to vibrate and induce inertia forces on them. Hence structures in such locations need to be suitably designed and detailed to ensure stability, strength and serviceability with acceptable levels of safety under seismic effects.

The interest of an engineer in earthquakes is mainly from design point of view. He studies them so that the structure he builds can safely withstand the earthquake shocks and the associated erratic ground motion.

At present, the principle of earthquake-resistant design of building has two aims:

1. The building shall withstand with almost no damage to moderate earthquake which have probability of occurring several times during life of a building.

2. The building shall not collapse or harm human lives during severe earthquake motions which have a probability of occuring less than once during the life of the building.

In the former case deformation of the structures remain within the elastic range.

In the latter case, they may exceed the elastic limit and the building should be designed with sufficient ductility to survive collapse.

In order to satisfy these aims, building design should conform following rules:

(a) The configuration of the building (Plan and elevation) should be as simple as possible.

(b) The formation should generally be based on hard and uniform ground.

(d) The structure of the building should be dynamically simple and definite.

(e) The frame of the building structure should have adequate ductility in addition to required strength.

(f) Deformations produced in a building should be held to values, which will not provide obstacles to safety use of building.

2.0 Classification

Intensity of an earthquake is measured by an instrument called Richter Scale. Classifications of earthquakes are as follows:

Slight: Magnitude up to 4.9 on the Richter Scale

Moderate: Magnitude 5.0 to 6.9

Great: Magnitude 7.0 to 7.9

Very Great: Magnitude 8.0 and above

- An earthquake of magnitude below 2.0 on the Richter Scale usually can’t be felt .

- An earthquake of magnitude below 4.0 on the Richter Scale don’t cause any damage.

- An earthquake of magnitude over 5.0 on the Richter Scale usually can cause minor damage.

- An earthquake of magnitude 6.0 and above is considered strong and cause

substantial damage.

- An earthquake of magnitude 7.0 and above is a major earthquake and renders worst possible damage.

Seismic Design Philosophy for Buildings:

Severity of ground shaking at a given location during an earthquake can be minor, moderate and strong. Relatively speaking, minor shaking occurs frequently, moderate shaking occurs occasionally and strong shaking rarely. For instance, on average annually about 800 earthquakes of magnitude 5.0-5.9 occur in the world, while the number is only about 18 for magnitude range 7.0-7.9, and the rare earthquake may occur only once in 500 years or once in 2000 years. As we know that the life of the building itself may be only 50 or 100 years, a conflict arises: whether to design the building to be “earthquake proof” where in there is no damage during the strong but rare earthquake shaking or should we do away with the design to building. Clearly, the former approach is too expensive and the second approach can lead to a major disaster. Hence, the design philosophy should lie somewhere in between these two extremes.

Seismic Risk to Buildings in India:

The construction may generally be classified into two types:

1. Non-Engineered Building Construction

2. Engineered Construction including building and infrastructure

Non-Engineered buildings are those which are spontaneously and informally constructed in various countries in the traditional manner without any or little intervention by qualified architects and engineers in their design. Such buildings involve field stone, fired brick, concrete blocks, adobe or rammed earth, a combination of wood with these traditional locally available materials in their construction . Cement and lime are sometimes used as mortar. Reinforced concrete lintels, floor, roof slabs and beams are also being increasingly used. In some cases, use of reinforced columns and beams is also made particularly for shopping centers and school buildings, but here also a post beam type simple concept is frequently adopted in a non-engineered manner without taking into consideration the stability of the system under horizontal seismic forces. Masonry buildings of all types, except those constructed with earthquake resisting elements, are at the greatest risk of heavy damage in seismic zoneIII and of destruction to collapse in zones IV and V.

Classification of Seismic Zones in India:

The earthquake resisting features specified to be incorporated while constructing any new building depend on the seismic intensity, zone in which the building is located, the base soil and the functional use of the building, whether considered important or ordinary. The extra cost of these resisting features will vary accordingly.

India is divided into 5 seismic zones in ascending order of magnitude of earthquake. The map was taken up for further revision after the Lathur earthquake of 1993. the resulting revised map published in IS:1893-2002(part I) where in the number of zones has been reduced to 4 i.e. II to V only, zone I being merged in zone II , and zone III now further expanded in the peninsular area.

The seismic zone map shows that of the total land area of the country, seismic zone V covers 12%, zone IV 18% and zone III about 27%, thus 57% could be subjected to damaging e earthquake intensity, masonry building in particular.

Indian Seismic Codes:

The Indian Standard Code to be followed for earthquake resistant structures are as follows:

IS 1893-2002, Indian Standard Criteria for Earthquake Resistant Design of Structures (5th Revision)

IS 4326-1993, Indian Standard Code of Practice for Earthquake Resistant Design and Construction of Buildings (2nd Revision)

IS 13827-1993, Indian Standard Guidelines for Improving Earthquake Resistance of Low Strength Masonry Buildings

IS 13920-1993, Indian Standard Code of Practice for Ductile Detaling of Reinforced Concrete Structures Subjected to Seismic Forces

IS 13935-1993, Indian Standard Guidelines for Repair and Seismic Strengthening of Buildings

Seismic Effects on Structures:

Inertia forces in structures:

Earthquake causes shaking of the ground. So the building resting on it will experience motion at its base. From Newton’s I Law of Motion, even though the base of the building moves with the ground, the roof has a tendency to stay in its original position. But since the walls and columns are connected to it, they drag the roof along with them. This tendency of the roof to continue to remain its previous position is known as inertia. In the building, since the walls or columns are flexible, the motion of the roof is different from that of the ground.

Horizontal and Vertical Shaking:

Earthquake causes shaking of the ground in all three directions- along two horizontal directions (x &y) and the vertical direction (z). During the earthquake, the ground shakes randomly back and forth along each of these directions. All structures are primarily designed to carry the gravity loads in the vertical direction. Hence, most structures tend to be adequate against vertical shaking. However, horizontal shaking along x and y directions remains a concern. Structures designed for gravity loads, in general, may not be able to safely sustain the effects of horizontal earthquake shaking. Hence it is necessary to ensure adequacy of the structures against horizontal earthquake effects.

Causes of Earthquake Damage:

The conventional masonry, particularly in un reinforced and non- engineered structures, being very weak in resisting tensile and shear stresses, leads to disastrous collapse of the entire building/ structure, causing heavy damage to property and loss of lives.

The main deficiencies in the conventional non- engineered/ un-reinforced masonry construction and other reasons for the extensive damage in such buildings are:

1. Heavy dead weight and very stiff buildings, attracting large seismic inertia forces.

2. Very low tensile strength, particularly with poor mortars.

3. Low shear strength, particularly with poor mortars.

4. Brittle behavior in tension as well as compression.

5. Weak connection between wall and wall.

6. Weak connection between roof and wall.

7. Stress concentration at corners of doors and windows.

8. Overall un symmetry in plan and elevation of the building

9. Un symmetry due to imbalance in the sizes and positions of openings in the wall.

10. Defects in construction, such as use of sub standard materials, unfilled joints between bricks.

3.0 Behavior of Brick Masonry Wall

Masonry buildings are brittle structures and one of the most vulnerable of the entire building stock under strong earthquake shaking. Thus, it is very important to improve the seismic behavior of masonry buildings. A number of earthquake-resistant features can be introduced to achieve this objective.

Ground vibrations during earthquakes causes inertia forces at locations of mass in the building. These forces travel through the roof and walls to the foundation. The main emphasis is on ensuring that these forces reach the ground without causing major damage or collapse. Of the three components of a masonry building (roof, wall and foundation, Fig1 (a)), the walls are most vulnerable to damage caused by horizontal forces due to earthquake. A wall topples down easily if pushed horizontally at the top in the direction perpendicular to the plane (termed weak direction), but offers much greater resistance if pushed along its length (termed strong direction, Fig 1 (b)).

Horizontal inertia forces developed at the roof transfers to the wall acting either in the weak or in the strong direction. If all the walls are not tied together like a box, the walls loaded in their weak direction tend to topple. (Fig 2(a))

To ensure good seismic performance, all walls must be joined properly to the adjacent walls. In this way, walls loaded in the weak direction can take advantage of the good lateral resistance offered by walls loaded in strong direction (Fig 2(b)). Further, walls also need to be tied to the roof and foundation to preserve their overall integrity.

Improving Behavior of Masonry Walls

Masonry walls are slender because of their small thickness compared to their height and length. A simple way of making these walls behave well during earthquake shaking is by making them act together as a box along with the roof at the top and foundation at the bottom. A number of construction aspects are required to ensure this box action.

Firstly, connections between the walls should be good. This can be achieved by

(a) Ensuring good interlocking of the masonry courses at the junction.

(b) Employing horizontal bands at various levels, particularly at the lintel level.

Secondly, the size of the doors and window opening need to be kept small. The smaller the opening, larger is the resistance offered by the wall.

Thirdly, the tendency of wall to topple when pushed in the weak direction can be reduced by limiting its length-to-thickness and height-to-thickness ratios. Design codes specify limits to these ratios. A wall that is too tall or too long in comparison to its thickness, is particularly vulnerable to shaking in its weak direction. (Fig (3))

4.0 Importance of Reinforcements in Masonry Building

The walls, if constructed with plain masonry would be incapable of resisting the magnitude of horizontal shear and bending forces imposed on them during earthquakes. For this reason, in the modern reinforced masonry systems, reinforcing steel is incorporated to resist the shear and tensile stresses, so developed. When these walls are subjected to lateral forces acting on them, they behave as flexural members spanning vertically between floors and horizontally between pilasters/ lateral walls. Therefore reinforcement in both vertical and horizontal directions is required to be provided to develop resistance against torsion.

Role of Horizontal Bands

Horizontal bands are the most important earthquake-resistant feature in masonry buildings. The bands are provided to hold a masonry building as a single unit by tying all the walls together. There are four types in a typical masonry building named after their locations in the building. They are:

(a) Plinth band: This should be provided in those cases where the soil is soft or uneven in their properties, as it usually happens in hilly areas. This band is not too critical.

(b) Lintel band: This is the most important band and covers all door and window lintel.

(c) Roof band: In buildings with flat reinforced concrete or reinforced brick roofs, the roof band is not required because the roof slab itself plays the role of a band. However, in buildings with flat timber or CGI sheet roof, a roof band needs to be provided. In buildings with pitched or sloped roof, the roof band is very important.

(d) Gable band: It is employed only in buildings with pitched or sloped roofs.

Design of Lintel Bands

During earthquake shaking, the lintel band undergoes bending and pulling actions. To resist these actions, the construction of lintel band requires special attention. Bands can be made of wood including bamboo strips) or of reinforced concrete (RC) (Fig.8); the RC bands are the best. The straight lengths of the bands must be properly connected at the wall corners. This will allow the band to support walls loaded in their weak directions by the walls loaded in their strong direction. Small lengths of wood spacers (in wooden band) or steel links (in RC bands) are used to make the straight lengths of wood runners or steel bars act together. In wooden bands, proper nailing of straight lengths with spacers is important. Likewise, in RC bands, adequate anchoring of steel links with steel bars is necessary.

Indian Standards:

The Indian Standards IS:4326-1993 and IS:13828-1993 provide sizes and details of the bands. When wooden bands are used, the cross-section of runners is to be at least 75mmx38mm and the spacers at least 50mmx30mm. When RC bands are used the

minimum thickness is 75mm, and at least two bars of 8mm diameter are required, tied across with steel links of at least 6mm diameter at a spacing of 150mm centers.

Role of Vertical Reinforcements in Walls:

Even if horizontal bands are provided, masonry buildings are weakened by the openings in their walls (Fig (9)). During earthquake shaking, the masonry walls get grouped into 3 sub-units, namely Spandrel masonry, Wall Pier masonry and Sill masonry.

When the ground shakes, the inertia force causes the small-sized masonry wall piers to disconnect from the masonry above and below. These masonry sub-units rock back and forth, developing contact only at the opposite diagonals (Fig. 10(a)). The rocking of a masonry pier can crush the masonry the corners. Rocking is possible when masonry piers are slender, and when weight of the structure above is small. Otherwise, the piers are more likely to develop diagonal (X-type) shear cracking (Fig. 10(b)); this is the most common failure type in masonry buildings.

During strong earthquake shaking, the building may slide just under the roof, below the lintel band or at the sill level. Sometimes, the building may also slide at the plinth level.

How Vertical Reinforcement Helps?

Embedding vertical reinforcement bars in the edges of the wall piers and anchoring them in the foundation at the bottom and in the roof band at the top (Fig 11), forces the slender masonry piers to undergo bending instead of rocking. In wider wall piers, the vertical bars enhance their capability to resist horizontal earthquake forces and delay the X-cracking. Adequate cross-sectional area of these vertical bars prevents the bar from yielding in tension. Further, the vertical bars also help protect the wall from sliding as well as from collapsing in the weak direction.

Protection of Openings in Walls:

The most common damage, observed after an earthquake, is diagonal X-cracking of wall piers, and also inclined cracks at the corners of door and window opening. When a wall with an opening deforms distorts and becomes more like a rhombus. Steel bars provided in the wall masonry all around the openings restrict these cracks at the corners

(Fig. 12). In summary, lintel and sill bands above and below openings and vertical edges, provide protection against this type of damage.

Structural Design:

Three important aspects to be considered in the design of earthquake resistant structures are given below:

1. The structure should be ductile, like the use of steel in concrete buildings. For these ductile materials to have an effect, they should be placed where they undergo tension and thus are able to yield.

2. Apart from ductility, deformability of structures is also essential. Deformability of structures is also essential. Deformability refers to the ability of a structure to dispel or deform to a significant degree without collapsing. For this to happen, the structure should be well- proportioned, regular and tied together in such a way that there are no area of excessive stress concentration and forces can be transmitted from one section to another despite large deformations. For this to happen, components must be linked to resisting elements

3. Damageability is another aspect to be taken into consideration. This means the ability of a structure to withstand substantial damage without collapsing. To achieve this objective “minimum area which shall be damaged in case a member of the structure is collapsed” is to be kept in view while planning. Columns shall be stronger than beams for that purpose and it is known as strong column and weak beam concept.

Tips for Earthquake-Resistant Design:

The building plan should be in a regular shape such as square or rectangular.
No wall in a room should exceed 6.0m in length. Use pilasters or cross walls for longer walls. In hilly terrain, it should not exceed 3.5m in length.
The height of each storey should be kept below 3.2m.
Don’t use bricks of crushing strength less than 35kg/cm2 for single storeyed building and of 50kg/cm2 for 2-3 storeyed building. Only solid and sound bricks/ concrete blocks should be used
Provide a R.C.C band of 4” thickness throughout the run along wall at lintel level passing over doors and windows.
The thickness of load bearing wall should be at least 200mm
The clear width between a door and nearest window should not be less than 600mm.
Location of a door or window from edge of a wall shall be 600mm minimum.

REPAIR OF CORROSION AFFECTED REINFORCED CONCRETE STRUCTURES

noreply@blogger.com (Civil Engineer) — Wed, 9 Jun 2010 13:00:00 +0530

The process of formation of rust over the surface of reinforcing bar and resulting in the depassivation of steel is known as “Corrosion”.

Corrosion of reinforcing steel is one of the most important and prevalent mechanisms of deterioration for concrete structures.

Corrosion process:

In order to understand the mechanism behind corrosion of reinforcing steel in concrete, one has to know about the chemical reactions involved in it.

In concrete, the presence of abundant amount of calcium hydroxide and relatively small amount of alkali elements, such as sodium and potassium, gives concrete a very high alkalinity with pH of 12 to 13. It is widely accepted that, at the early age of the concert, this high alkalinity results in the transformation of a surface layer lf the embedded steel to a tightly adhering film, that is comprised of an inner dense spinal phase in epitaxial orientation to the steel substrate and an outer layer of ferric hydroxide. As long as this film is not disturbed, it will keep the steel passive and protected from corrosion.

When a concrete structure is often exposed to atmosphere, chloride ions from these will slowly penetrate into the concrete, mostly through the pores in the hydrated cement paste. The chloride ions will eventually reach the steel and then accumulate to beyond a certain concentration level, at which the protective film is destroyed and the steel begins to corrode, when oxygen and moisture are present in the steel concrete interface.

Once corrosion sets in on the reinforcing steel bars, it proceeds in electrochemical cells formed on the surface of the metal and the electrolyte or solution surrounding the metal, each cell is consists of a pair of electrodes (the anode and its counterpoint, the cathode) on the surface of the metal, a return circuit, and an electrolyte. Basically, on a relatively anodic spot on the metal, the metal undergoes oxidation (ionisation), which is accompanied by production of electrons, and subsequent dissolution. These electrons move through a return circuit, which is a path in the metal itself to reach a relatively catholic spot on the metal, where these electrons are consumed through reactions involving substances found in the electrolyte. In a reinforced concrete, than anode ad the cathode are located on the steel bars, which also serve as the return circuits, with the surrounding concrete acting as the electrolyte.

Corrosion: Structural effects:

In the case of concrete structures the first direct effect of the reinforcement corrosion is its section decreases due to the corroding process. Iron oxide (Rust) resulting reinforced concrete structures and their effect induces internal stresses in the concrete, which may lead to cracking or even spalling of concrete.

Induced Cracking of the concrete

Corrosion also may reduce the steel elongation at maximum load, affection the structure.

Accordingly, reduction of structural capacity of reinforced concrete elements affected by rebar corrosion is mainly due to following three main phenomena, which are direct consequence of corrosion:

Reduction of rebars section due to corrosion.

b. Reduction of bond strength.

Loss of concrete integrity due to cover cracking and spalling.

However corrosion of reinforcing steel can occur by two major situations, they include:

Carbonation
Chloride contamination.

Carbonation:

Carbonation is a process in which carbon dioxide from the atmosphere diffuses through the porous concrete and neutralizes the alkalinity of concrete. The carbonation process will reduce the pH to approximately 8 to 9 in which the oxide film is no longer stable. With adequate supply of oxygen and moisture, corrosion will start. The penetration of concrete structures by carbonation is a slow process, the rate of which is determined by the rate at which carbon dioxide penetrates into the concrete. The rate of penetration primarily depends on the porosity and permeability of the concrete. It is rarely a problem on structures that are built with good quality concrete with adequate depth of cover over the reinforcing steel.

Chloride contamination:

Chloride ions can enter into the concrete from the chloride containing admixtures that are used to accelerate curing or from seawater in marine environment. If the chlorides are present in sufficient quantity, they disrupt the passive film and subject reinforcing steel to corrosion. The levels of chloride required to initiate corrosion are extremely low. Field experience and research have shown that on existing structures subjected to chloride ions, a threshold concentration of about 0.026% (by weigh o concrete) is sufficient to break down the passive film and subject the reinforcing steel to corrosion. This equals to 260-ppm chloride.

The removal of the passive film from reinforcing steel leads to the corrosion process. Chloride ions within the concrete are usually not distributed uniformly. The steel areas exposed to higher concentrations of chlorides start to corrode, and breakdown of the oxide film eventually occurs. In other areas the steel remains passive.

The rate of carbonation in concrete is directly dependent on the water cement ratio of the concrete i.e., higher the ratio the greater is the depth of carbonation in the concrete

Causes for failures:

The following are the major causes for failures of structures:

Structural deficiency due to defects in construction, use of inferior and substandard materials, poor workmanship, and negligence in quality control and supervision.
Damages caused due to fire, foods, earthquakes, etc.
Chemical deterioration and marine environments
Damages caused due to abrasion, wear and tear impact, dampness, etc,
Movements of concrete caused due to settlements of foundation, thermal expansion etc.

MATERIALS FOR REPAIR

The materials used for concert repair are generally cement based or Epoxy based. They are,

Cement/Sand mortars
Polymer Latex
Epoxy Resins
Polyester Resins

STRUCTURAL REPAIR BASED ON EXTENT OF DAMAGE

The structural repairs to be carried out in corrosion affected reinforced concrete structures to enhance its service life can be classified as follows:

1. Repairs to spallen concrete portions (steel and concrete)

Cement based repairs
Resin based repairs

2. Large volume repair

Poured concrete
Prep laced concrete

3. Sealing of cracks

Cracks with no further movements expected
Cracks with further movements expected

4. Surface coatings

5. Dry packing

Repair of a severely corrosion damaged member, where cover

Concrete has spallen and reinforcement (reduced in cross-sectional area) has been exposed.

Step 1

The repair process is started by cutting away all the loose and deteriorated concrete until the hard core is reached preferably behind the corroding reinforcement.

Step 2

All exposed reinforcements must be thoroughly cleaned. Loose rust or any contamination is removed by abrasive blast cleaning. Wire brushing by hand is not usually effective.

Step 3

The portions of steel bars severely corroded require replacement. This is achieved by cutting away the corroded portions and replacing with new bars of the same type and size, either welded or tied to the existing bars.

Step 4

After the corrosion affected bars are replaced in position, immediately a protective primer (Zinc, neat resin or any other suitable coating) is applied. The primer chosen should be such that it should good adhesive strength and good adhesion to subsequent repair layers.

Step 5

In order to build up the section, either cement based repair, or Resin based repair can be carried out.

Typical repair procedure for corrosion damaged concrete

Cement based repairs:

Step 6

i) The slurry (bonding coat) is applied to all concrete surfaces to which bond is required and the patching mortar (readily available in pre-weighed packets) is applied, while the slurry is still tacky. (Care should be taken to wit the concrete surface before the application of the material but there must be no standing water left on the surfaces).

ii) After the prepared surfaces have been coated with bonding agent or a coating of neat cement slurry, the repair material consisting of 1:3(cement and sand) is applied in layers not exceeding 20mm thick. Each layer is to be keyed to receive the succeeding layers. The outer layers of cement should not be thicker than the inner layers. This is required, in order to prevent failure due to shrinkage stresses.

It should be ensured that the cement-based materials used in repairs do not dry out quickly. The method is curing depends on the local conditions. Water soaked covers and curing membranes are common ways of protection.

Resin based repairs

Step 7

As usual, the priming coat is applied over the prepared surfaces to protect the surfaces. The interval between coats should not be too long; otherwise there will be bond failure.

Resin-based materials cure by exothermic chemical reaction immediately, when the constituents are mixed. It is essential that the materials should be well compacted to become impermeable, because they do not protect the steel by alkalinity.

Large volume repair

When a large volume o repair material is to be placed in members that have been extensively damaged, it becomes necessary to fix some kind o formwork and fill it with concrete or grout. The concrete is usually placed in conventional ways (poured concrete) or it may be formed by injecting grout into a mass of dry aggregate (under water work concrete).

Poured concrete

Defective concrete is first removed and loose concrete is chipped away from the face and around the reinforcement. Additional reinforcement can be provided by securely fastening it to the existing bars. It is necessary to protect the reinforcement by applying coating in the form of corrosion inhibiting paint like cement based polymer slurry or a resin based slurry. The formwork is so designed that the concrete fills it completely without leaving any air pockets. The joints in the formwork are sealed completely to avoid any leakage. Depending on the thickness to be poured, aggregate of maximum 20mm size (for thickness greater than 100mm) is adopted in the concrete mix, with suitable shrinkage compensating agent. In order to ensure good compaction of concrete, material vibration or external vibration using a mechanical hammer on the formwork can be imparted.

Replaced concrete

The technique is best suited for certain types of repair, particularly in under water work. In this method the formwork is erected in the normal way but it is first filled with clean specified (depending of thickness) coarse aggregate. Later cement grout is pumped into the forms from bottom until all the voids are filled as the air or water is vented at the top. It is essential that the formwork is watertight and is designed to withstand the full hydrostatic head of grout. This method offers quality concrete without segregation with minimum during shrinkage. This disadvantage is that the injected cement paste is prone to bleeding

Sealing of cracks

Sealing of cracks by repair materials will be effective only when proper materials are injected. For this, the cause of crack has to be determined. If the cause of the crack is such that it is unlikely to recur, then it can be filled with a rigid material. But, if the crack is caused due to movement and that is likely to continue then any attempt to seal the crack against further movement may cause a new crack along the side of the old one.

Repair of cracks (where no further movement is expected)

Such cracks can be sealed to prevent moisture penetration by simply brushing latex emulsion of low viscosity or cement paste containing fine quartz powder filler. The procedure for carrying out this type of repair is as follows:

Step 1

The crack is thoroughly cleaned using compressed air.

Step 2

Superficial seal is applied over the crack at the surface by using a fast setting polyester resin or a thermoplastic material into which injection nipples are fixed at intervals.

Step 3

Injection is started at the lowest point and when resin reaches the next higher point, the injection gun is moved up to the next and the lower point is sealed. The process is continued until the whole crack gets sealed. The pressure used is carefully controlled to avoid bursting of the seal and concrete scale work.

Repair of cracks (where further movement is expected)

When a crack is subjected to continuing movement, it is absolutely necessary to reduce the strain in it to reasonable amount. This can be easily done by widening the crack at the surface and sealing it with an elastic material such as polysulphide rubber or a performed neoprene strip.

Surface coatings

It is necessary, that after the completion of repair work, to treat both the repaired areas and the rest of the structure with some coatings, principally, to reduce the permeability of concrete, to moisture, carbon dioxide, and other aggressive agents. The coatings further can also give aesthetic look to the structure by containing the patches, discolouration and stains and match colour and textures.

Several coatings are available in the market, which can be readily used on the repaired surfaces as per the instructions of the manufacturer. Siloxene based coatings prove to be effective.

Dry packing

Dry packing or plugging is the hand placement of a low w/c ratio mortar followed by ramming or tamping of mortar into place producing a intimate contact between new and existing work. The method is applicable to dormant cracks in a structure. Shrinkage is considerably reduced. Provides good strength and water tightness increasing the durability. Care is to be taken to use well-graded sand in the mortar mix.

USE OF BAMBOO AS CONSTRUCTION MATERIAL

noreply@blogger.com (Civil Engineer) — Wed, 9 Jun 2010 12:50:00 +0530

The world timber demand is increasing at a rapid rate but the timber supply is depleting. It’s been found through research that bamboo can suitably replace timber and other materials in construction and other works. Industrially treated bamboo has shown great potential for production of composite materials and components which are cost-effective and can be successfully utilized for structural and non-structural applications in construction. Bamboo is one of the oldest traditional building materials used by mankind.

The bamboo culm, or stem, has been made into an extended diversity of products ranging from domestic household products to industrial applications. Examples of bamboo products are food containers, handicrafts, toys, furniture, flooring, pulp and paper, boats, charcoal, musical instruments and weapons. Bamboo is quite common for bridges, scaffolding and housing, but it is usually used as a temporary exterior structural material. In many overly populated regions of the tropics, certain bamboos supply the one suitable material that is sufficiently cheap and plentiful to meet the extensive need for economical housing. It has been used in bicycles, windmills, scales etc. Its uses are broad and plentiful.

With the advancement of science and technology and the tight supply of timber, new methods are needed for the processing of bamboo to make it more durable and more usable in terms of building materials. Studies have been carried out on the basic properties and on processing of bamboo into various kinds of composite products. Bamboo has several unique advantages like ability to grow fast with a high yield and also it matures quickly. Additionally bamboo can be grown abundantly and that too at a lower cost which makes it more economical.

Processing of Bamboo and Treatment of Bamboo:

It has been found that bamboo panel composites have great potential due to their better strength, dimensional stability and other characteristics. Main characteristic features, which make bamboo as a potential building material, are its high tensile strength and very good weight to strength ratio. It can be easily worked upon by simple tools and machines. The strength-weight ratio of bamboo also supports its use as a highly resilient material against forces created by high velocity winds and earthquakes. Above all bamboo is renewable raw material resource from agro-forestry and if properly treated and industrially processed, components made by bamboo can have a reasonable life of 30 to 40 years. Though natural durability of bamboo varies according to species and the types of treatments, varied uses and applications in building construction have established bamboo as an environment-friendly, energy-efficient and cost-effective construction material.

Through several technologies mat based composites from bamboo have been developed like Bamboo Mat Board (BMB), Bamboo Mat Veneer Composite (BMVC) and Bamboo Mat Corrugated Sheets (BMCS).

The mat composites are manufactured by hot pressing the woven strips of bamboo. Thin bamboo strips called as “slivers” of width 0.6 to 1.0mm are manually woven into a mat of different sizes and patterns of which herringbone is the most common pattern in which the slivers are at an angle of 45⁰ with respect to the edges of the mat. Then the mats are dipped in Phenol formaldehyde resin which is a chemical preservative to enhance resistance against decay and termites, later they are dried and 2 to 5 mats are assembled and hot pressed to the required thickness.

For BMVC mats wood veneers are placed in-between the layers of bamboo mats. The property of BMVC mainly depends on the properties of the inter-leaved wood veneers.

Preservation and Treatment

As bamboo has less natural durability it requires chemical treatment for longer life. Bamboos have low natural durability (1 to 3 years) against attacks by fungi and insects. They are very difficult to be treated by normal preservative methods in dry condition since their outer and to some extent inner membranes are impermeable to liquids. The treatment of bamboo is, therefore, best carried out in green conditions. The following are methods used for bamboo preservation as per IS 401-2001-“code of practice for timber preservation” and IS 9096-1979-“code for practice for preservation of bamboo for structural purposes”:

Types of Preservatives:

· Coal Tar Creosote -This is a fraction of coal tar distillate with a boiling point range above 200°C and is widely used admixed with fuel oil in the ratio of 50:50. The fuel oil ensures stability to creosote against evaporation and bleeding from the treated bamboos. Creosote has high performance; it is non-corrosive and provides good protection from termites.

· Copper Chrome Arsenic Composition - A typical composition of this preservative comprises of coppersulphate, arsenic pentoxide and sodium or potassium dichromate in proportion of 3: 1:4.

· Copper Chrome Boric Composition: A typical composition of the preservative comprises boric acid, copper sulphate and sodium or potassium dischromate in the proportion of 1: 5: 3: 4.

· Copper Chrome Zinc Arsenic Composition - A typical composition of this preservative comprises 28 parts of arsenic acid 25 parts of sodium arsenate, 17 parts of sodium dichromate and 30 parts of zinc sulphate.

· Chromated Zinc Chloride - This consist of zinc-chloride and sodium or potassium dichromate in the ratio of 81.5: 18.5.

· Boric Acid Borax - This has been used successfully against lyctus borers. A mixture of 2:5 percent of each is found more suitable.

Methods of Treatment:

· Surface Application: this is done by brushing, spraying or dipping of timber in preservative solution for the required period.

· Soaking process: the debarked timber is submerged in the preservative solution for sufficient period till the desired absorption is obtained.

· Hot & Cold process: timber is preserved in the solution and then heated to temperature of about 90⁰C and maintained at this temperature for suitable period and then cooled until required absorption is obtained.

· Boucherie process: it makes use of water soluble preservatives and hydraulic pressure.

· Pressure process: it can be employed to any type of preservative and is used where maximum absorption of the preservative is required.

Bamboo as Construction Material:

Through research it has been found that some species of bamboo have ultimate tensile strength same as that of mild steel at yield point and this coupled with other merits boosts the usage of bamboo as construction material.

Bamboo is a versatile material because of its high strength-to-weight ratio, easy workability and availability. Bamboo needs to be chemically treated due to their low natural durability. It can be used in different ways for roof structure as purlins, rafters and reapers, for flooring, doors and windows, walling, ceiling, man-hole covers etc.

3.1 Bamboo Trusses:

The bamboo has strength comparable to that of teak and sal. An experiment with the construction and testing of a 4m span truss made of round bamboo and different jointing techniques for web-chord connections gave results that were matching with the strength of timber.

3.2 Bamboo Roofs Skeleton:

It consists of bamboo truss or rafters over which solid bamboo purlins are laid and lashed to the rafter by means of G.I.wire. A mesh of halved bamboo is made and is lashed to the purlins to cover the roof.

3.3 Bamboo walling/ceiling:

As the bamboo material is light in weight it is more advantageous in earthquake prone areas as its chances of falling are very less and even if it falls it can be re-erected easily with less human and property loss with least efforts and minimum cost. Bamboo walls can be constructed in different modes like

· Whole stem, halved or strips of bamboo can nailed to one or both the sides of the bamboo frame

· Split bamboo mats can be fastened to the bamboo posts or mats can be woven, mud can also be applied to both sides of such mats

· Bamboo strips nailed to bamboo frame or posts for interior walling

· Cement or lime plastering can be done on the mud covering for better appearance and hygiene.

It has been found that the bamboo in the vertical position is more durable than in horizontal direction. For partition walls only single layer of bamboo strips are used.

3.4 Bamboo Doors and Windows:

Bamboo frames can replace timber frames appropriate to function. Bamboo mat shutters fixed to bamboo frame or a panel of bamboo board fixed to the frame which is hinged to the wall can be used as door. Small framed openings hinged to the top in the wall can serve as windows.

3.5 Bamboo Flooring:

Bamboo can be used as flooring material due to its better wear and tear resistance and its resilience properties. Whole culms act as frame work and the floor covering is done using split bamboo, bamboo boards, mats etc by means of wire lashing these to the frame.

3.6 Reed Boards:

Reed boards are made by flat pressing the reed at high temperatures. These reed boards are used in elements like flooring, walls, ceiling and roofing. They can also be used for partitions, doors, windows etc.

3.7 Scaffolding:

Bamboo poles lashed together have been used as scaffolding in high rise structures due to their strength and resilience. The timber planks can be replaced with bamboo culms and these can be lashed to the vertical culms.

Strength Properties of Bamboo:

Experimentally it has been found that the ultimate tensile strength of some species of bamboo is comparable to that of mild steel and it varies from 140N/mm²- 280N/mm². This together with other properties has made Bamboo a more visible option as a construction material.

It has also been found that bamboo acts very well in buckling but due to low stresses than compared to steel and due to it not being straight it may not be very good.

Further, it has been established that in seismic zones the failure of bamboo is very less as the maximum absorption of the energy is at the joints. Cellulose is the main component present in bamboo which is the main source of mechanical properties of bamboo.

Some specific properties of Bamboo are as given below:

Specific gravity - 0.575 to 0.655

Average weight - 0.625kg/m

Modulus of rupture - 610 to 1600kg/cm²

Modulus of Elasticity - 1.5 to 2.0 x10⁵kg/cm²

Ultimate compressive stress- 794 to 864kg/cm²

Safe working stress in compression - 105kg/cm²

Safe working stress in tension - 160 to 350kg/cm²

Safe working stress in shear- 115 to 180kg/cm²

Bond stress - 5.6kg/cm²

5.0 Conclusion:

Scientific studies have shown that Bamboo can satisfy the various structural requirements and also due to its technical performance Bamboo can be used as a construction material for various structural components. The important advantages which make Bamboo a more suitable material are:

· It is economical and helps achieve cost effective construction.

· Bamboo is a fast growing species and it is a renewable resource which can be cultivated in most types of soil.

· The designs of the components being simple, there is no need of highly skilled labour.

· The dependency on the natural forests for wood will be reduced thus contributing to the protection of the environment.

· As it can grow in many types of soil, bamboo cultivation is suitable for rehabilitation of degraded forests and other waste lands thus converting them into fertile lands to some extent.

· Creation of employment opportunities especially for the rural people as the Bamboo mats have to be manually woven before making them into Bamboo Mat Boards, Bamboo Mat Veneer Composites and Bamboo Mat Corrugated Sheets.

· Thus due to all the above aspects there will be overall welfare of the society, particularly of the economically weaker section.

ADVANTAGES & BENEFITS OF SYNTHETIC FIBRES IN CONCRETE FLOORING & PLASTERING APPLICATIONS

noreply@blogger.com (Civil Engineer) — Tue, 8 Jun 2010 07:11:00 +0530

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• The idea of using fibers in concrete materials dates back to Roman and Egyptians period

• Romans included bits of horsehair in the construction of

• ROMAN COLISEUM which was built in 80 AD

• The Egyptians used straw in their bricks used for constructions

INTRODUCTION TO SECONDARY REINFORCEMENT OF

CONSTRUCTION BY FIBRES

• Plastic shrinkage and plastic settlement cracks

• Less abrasion resistance and impact resistance of floors

• Weak construction joints

• Periodic maintenance of floors due to less durability

• Faster wearing of top floor surface

DRAW BACKS IN CONCRETE FLOORING WORKS

• Development of plastic shrinkage cracks in the initial stage of plastering

• High rebound loss of mortar

• High water and moisture absorption from external environment

• Less cohesive mix due to segregation

• Development of thermal and drying shrinkage cracks at the hardened surface

of plastering

• More maintenance of the walls required in terms of frequent waterproofing and painting of the buildings

• Ugly crack patches

DRAW BACKS IN PLASTERING WORKS

• Generation 1 - Vegetable Fibers - Straw, Jute and Cotton, Coconut Coir

• Generation 2 - Horse hair, Sheep’s Wool

• Generation 3 - Glass, Polyester, Nylon, Polypropylene and Steel

DEVELOPMENT OF FIBER REINFORCEMENT

• Glass - Expensive, Causes itching, Hazardous

• Steel - Corrosion, Dead Weight, Expensive, Mixing Problem

• Nylon - Very Expensive

COMPARISON WITH VARIOUS TYPES OF FIBERS

• Holds aggregates & does not allow separation of coarse aggregate due to

vibration /gravity

• Results move uniform concrete to concrete

• Fiber allows slow transfer of water to surface, resulting in reduction of cracks

WHAT FIBRE DOES?

• ACCEPTANCE CRITERIA FOR CONCRETE WITH SYNTHETIC FIBERS

• Synthetic fibers are added to concrete to reduce plastic shrinkage cracking of reinforced concrete and structural plain concrete and/or to reduce shrinkage and temperature cracking in structural plain concrete slabs on grade

• Consideration to be given to the volume, size and type of fibers used

• The fibers are regarded as an admixture and are used in addition to any structural reinforcement, shrinkage and temperature reinforcement and joints as required in the applicable code

• The fibers may be used in concrete over steel deck construction

• The fibers may be used in fire-resistive construction on steel decks

· Fibers were instrumental in reducing shrinkage cracks

· Rebound loss of the mortar has been reduced to 10 % instead of 30 to 40 % with out fibers in the mortar

· There is no Dampness and leakage of plastered walls

· Better finish of wall surface

· Increased strength of mortar due to which more durable and long lasting constructions

· Savings due to economic mix designs and more durable plastered surface

· Compressive strength of plaster was increased by over 15-20%

· Results in Cement savings up to 3%

· Increase in labour productivity by over 5%

· ADVANTAGES & BENEFITS OF USING FIBERS IN PLASTERING
AT OUR PROJECTS

· The use of fibers has improved the abrasion resistance of concrete floors to
moving loads

· No appearance of plastic shrinkage and plastic settlement cracks on the concrete floor surface

· Service life of the floor is enhanced due to high durable concrete produced with synthetic fibers

· Improved impact resistance of floors to point loads

· Concrete mix with fibers was cohesive with better workability

· Compressive strength of plaster was increased by over 8-10%

· ADVATAGES & BENIFITS OF USING FIBERS IN CONCRETE FLOORING WORKS

· Use of Synthetic Fibers in all construction applications should be encouraged by the construction industry

· Different types of fibers should be developed to address each specific need of construction applications

· Construction industry should encourage new technologies like fibers reinforcement in construction to a larger extent for improving the durability and serviceability of the building and structures

Presentation on APPLICATION OF INTELLIGENT TRANSPORT SYSTEM FOR TRAFFIC CONTROL AND SAFETY

noreply@blogger.com (Civil Engineer) — Thu, 3 Jun 2010 21:24:00 +0530

To download in PPT format: Link1, Link2, Link3, Link4

APPLICATION OF INTELLIGENT TRANSPORT SYSTEM FOR TRAFFIC CONTROL AND SAFETY

• ITS is a comprehensive system which can prepare safe smooth and pleasant environment for road traffic.

• The fundamental element for ITS is communication technology between road infrastructure and vehicle.

• ITS comprises of broad range wireless and wireline communication based information.

• ITS utilize existing roadways more efficiently to reduce congestion, delay, minimize accidents and improve air quality.

• ITS provide tools for skilled transportation professionals to collect and analyze the data about the performance of the system during peak hours.

• Thus ITS is an international program intended to improve surface transportation system through advanced technologies.

BENEFITS OF ITS

• Reduced rush hour congestion and delay.

• Increased safety and personal security.

• Time savings and operation efficiencies.

• Reduced fuel consumption and emissions.

• Improved customer service and reduced frustration.

• Reduced road accidents and enhanced economic productivity.

TRAFFIC PROBLEMS

• Traffic congestion and delay.

• Inadequate public transportation facilities, which run behind scheduled, causing inconvenience to public.

• Shortage of man power.

• Increase in air and noise pollution due to increase in number of vehicles.

• Acute parking problem in urban areas.

• Non-cooperation from public for any new system or changes.

• High accident rates due to varying speed of vehicles and lack of discipline among road users.

• Absence of effective monitoring and prevention of traffic violation.

CLASSIFICATION OF ITS

• Advanced Public Transportation System (APTS).

• Advanced Traveler Information System (ATIS).

• Advanced Traffic Management System (ATMS).

• Automated Highway System (AHS).

• Incident management system.

• Electronic Toll Collection System (ETC).

• Advanced Warning System (AWS).

• Vehicle Information and Communication System (VICS).

• Video transmission.

ADVANCED PUBLIC TRANSPORTATION SYSTEM

APTS is a technology that increase the efficiency and safety of public transportation system.

The goal of APTS is to provide more information to public to make effective decision and to increase travelers convenience and rider ship.

asically this system helps to smoothen out public transportation related problems.

ADVANCED TRAVELER INFORMATION SYSTEM

• ATIS is a new technology helps in providing accurate and timely information to travelers.

• They deliver data directly to travelers empowering them to make better choices.

• This system helps in optimizing the transportation planning process.

ADVANCED TRAFFIC MANAGEMENT SYSTEM

• Monitor the flow of traffic making appropriate decision in a timely manner.

• Employs inexpensive detectors, cameras and communication system to control the flow of traffic.

• Optimize signal timings on major arterials.

AUTOMATED HIGHWAY SYSTEM

• AHS is a specially equipped highway lane, where the vehicles are automatically controlled by the system, not by the driver.

• The system helps in keeping the vehicle in the same lane.

• The AHS lanes and vehicles which operate on them are likely to have special sensors, computers and communication devices to permit automated control.

INCIDENT MANAGEMENT SYSTEM

• They offer real time information about traffic conditions through variable message sign to warn accidents or other delays.

• Variable message sign is a board which provide information to the motorist of the upcoming hazards.

• Enables authorities to identify and respond to vehicle crashes or breakdowns with the most appropriate and timely emergency services, thereby minimizing recovery time.

VARIABLE MESSAGE SIGN

ELECTRONIC TOLL COLLECTION SYSTEM

• ETC is a system by which drivers can pay tolls without having to stop at a toll booth.

• The collection of fees is performed electronically by way of equipment installed in the vehicle and sensors at toll location.

• ETC is based on vehicle roadside communication system.

ELECTRONIC TOLL COLLECTION SYSTEM

HERE IS HOW IT WORKS:

Conceptual image of ETC

ADVANCED WARNING SYSTEM

• This system warns the present accident to be caused when traffic slows down abruptly due to road conditions.

• The information given to the driver when the vehicles come closer either from front or back is conveyed through AWS which helps in preventing road crashes.

VEHICLE INFORMATION AND COMMUNICATION SYSTEM

• In this system, the drivers are provided with real time information on the traffic conditions

• They update all the road users about the traffic conditions and other information like congestion, jams, roadblocks, pollution levels etc.

• The information is given via FM band or through road maps quickly showing the traffic conditions in surrounding areas.The driver can use this information to select the best route by using in vehicle monitor.

IN VEHICLE MONITOR

SCHEMATIC INFORMATION DISPLAY OF ROAD MAP

Radio beacons (expressway linking Tokyo and Osaka in Japan)

VIDEO TRANSMISSION

• This system is used for detecting unauthorized vehicles on restricted corridors and parking areas.

• Vehicles with speed violations can be captured along with registration numbers.

TRAFFIC SENSORS AND TRAFFIC CAMERAS

NECESSITY FOR USING ITS

• Provides novel application by smart technology.

• Systematically employs advanced technologies in the field of transportation to enhance benefits for road users.

• Reduction in road crashes.

• Improves the existing transportation services through interconnected embedded technologies.

ITS IN INDIA

• In India 70 state transport undertakings which together own and operate 1,13,000 buses and provide mobility to 65 million passengers a day, across the length and breadth of the country.

• The most important task of ITS India will be the dissemination of ITS knowledge and imparting training for new professionals.In 1980’s number of developed countries started using advanced system to control and regulate traffic.This is still to develop in India to suit our local ambience.

• The very first equipment to be used in Indian environment was electronic toll collection along the newly created expressways i.e, Delhi-Noida, Ahmedabad-Mehasana and Mumbai-Pune, which is functioning satisfactorily.

• What is needed in the present context is the mind set of policy makers to cooperate for the adaptation to the new system.

CONCLUSION

• The potential of ITS technologies in improving the efficiency of transportation sector in India appears to be very promising based on the experience of other countries.

• A national strategic ITS plan for India is needed for the effective development and deployment.

• Some of the ITS technologies like fleet management system, AWS, ETC, Incident management system can be applied to achieve an efficient transportation system.

• Since ITS technology is as old as 20 years in the world, India will have to pick up this for updating and be on par with developed countries in modern transportation requirements.

REFERENCES

• Prof.M.N.Sreehari, MSRIT, Bangalore, December 2003, “Intelligent Transport System”, Technical proceedings:Build Tech.

• http://www.itsa.org

• http://www.fibre-optics.info/articles/its-overview.htm

• http://www.tele.soumu.go

• http://www.aist.go.jp/aist-e/latest_research

• http://www.ircc.iitb.ac.in/~fellowship/civil%20dept%20

brochures.pdf

THANK YOU

Civil Engineering

INTERLINKING OF RIVERS IN INDIA

Need for Interlinking OF RIVERS: -

Requirement of water: -

Concept of interlinking of rivers: -

OBJECTIVES OF NWDA

NATIONAL PERSPECTIVE FOR WATER RESOURCES DEVELOPMENT

(a) Himalayan Component

Benefits from peninsular and Himalayan rivers development components

CASE STUDY OF BIHAR

RECURRENCE OF FLOODS AS CONCLUSIVE EVIDENCE OF SURPLUS

ENVIRONMENTAL, ECOLOGICAL AND HUMAN IMPACT

EXISTING INTER BASIN TRANSFER PROJECTS

The Periyar project

Rajasthan canal project

ABROAD

Promises

Pitfalls

APPLICATION OF “FUZZY CONCEPTS” IN CIVIL ENGINEERING

ANAEROBIC DIGESTION

The Digestion Process

How does AD work?

Digester Designs

EFFLUENT/ DIGESTATE UTILISATION

CARTOGRAPHY

Photographic imaging

Electronic imaging

IMAGE PROCESSING

THEMATIC INFORMATION EXTRACTION

SOIL STABILISATION

SILICA FUME

Chemical composition of silica fume

Item

Requirement

Physical characteristics

Workability:-

Bleeding and segregation:-

Properties of hardened silica fume concrete

Creep:-

Alkali- aggregate reaction

Resistance Corrosion of embedded steel

Freeze – thaw resistance

Cementitious application of silica fume

OFFSHORE PLATFORMS

How it works

SELF COMPACTING CONCRETE

HIGH PERFORMANCE CONCRETE

FORMWORK

FLY ASH

EARTHQUAKE RESISTANT CONSTRUCTION

REPAIR OF CORROSION AFFECTED REINFORCED CONCRETE STRUCTURES

The process of formation of rust over the surface of reinforcing bar and resulting in the depassivation of steel is known as “Corrosion”.

Induced Cracking of the concrete

MATERIALS FOR REPAIR

STRUCTURAL REPAIR BASED ON EXTENT OF DAMAGE

1. Repairs to spallen concrete portions (steel and concrete)

2. Large volume repair

Repair of a severely corrosion damaged member, where cover

Concrete has spallen and reinforcement (reduced in cross-sectional area) has been exposed.

Step 1

The repair process is started by cutting away all the loose and deteriorated concrete until the hard core is reached preferably behind the corroding reinforcement.

Step 2

All exposed reinforcements must be thoroughly cleaned. Loose rust or any contamination is removed by abrasive blast cleaning. Wire brushing by hand is not usually effective.

Step 3

The portions of steel bars severely corroded require replacement. This is achieved by cutting away the corroded portions and replacing with new bars of the same type and size, either welded or tied to the existing bars.

Step 4

After the corrosion affected bars are replaced in position, immediately a protective primer (Zinc, neat resin or any other suitable coating) is applied. The primer chosen should be such that it should good adhesive strength and good adhesion to subsequent repair layers.

Step 5

In order to build up the section, either cement based repair, or Resin based repair can be carried out.

Cement based repairs:

Step 6

It should be ensured that the cement-based materials used in repairs do not dry out quickly. The method is curing depends on the local conditions. Water soaked covers and curing membranes are common ways of protection.

Resin based repairs

Step 7

As usual, the priming coat is applied over the prepared surfaces to protect the surfaces. The interval between coats should not be too long; otherwise there will be bond failure.

Resin-based materials cure by exothermic chemical reaction immediately, when the constituents are mixed. It is essential that the materials should be well compacted to become impermeable, because they do not protect the steel by alkalinity.

Large volume repair

Repair of cracks (where no further movement is expected)

Such cracks can be sealed to prevent moisture penetration by simply brushing latex emulsion of low viscosity or cement paste containing fine quartz powder filler. The procedure for carrying out this type of repair is as follows:

Step 1