Building Construction

Tolerance Limits

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Sample Question for Paper 5 Building Materials and Technology

Tolerance limits for construction are usually stated in the
A. wall sections
B. specifications
C. bills of quantities
D. production drawings

Ans: B

Tower Crane

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wheelbarrow

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Building (Construction) Regulation 90

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Every building shall be designed and constructed so as to

inhibit the spread of fire within the building and to nearby buildings by dividing the building into compartments;
provide adequate resistance to the spread of fire and smoke by the separation of different uses in a building by compartment walls and floors and by the separation of the building from any adjoining building or site;
maintain the stability of the building in case of fire;
provide adequate resistance to the spread of fire over the roof of one building to another having regard to the position of the building.

Building (Construction) Regulation 3

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All materials used in any building works or street works shall be:

of a suitable nature and quality for the purposes for which they are used;
adequately mixed or prepared; and applied, used or fixed so as to perform adequately the functions for which they are designed.

PNAP (Practice Notes for Authorized Persons, Registered Structural Engineers and Registered Geotechnical Engineers)

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include

ADM (Administration)
APP (Application)
ADV (Advice)

Raking Shore

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Raking Shore: A shore that is leaning at an angle (on the rake) to support the side of a building or other structure. The shore takes any thrust from the walls to the ground.
Single Raker Shore: A shore with only a single raking member, either timber or steel, aimed at a specific portion of a wall.
Double Raker Shore: A shore with two rakers to support a larger and higher section of wall.

A Khmer temple in the Word Heritage listed Angkor Wat Historical Area. As you can see the 800 years old structures are in need of support. In fact a lot more than they are getting.
The art of shoring up old or damaged building is a very delicate one and should only be done by experts, preferably under the supervision of a good structural engineer. In cases like the one shown above there is a very real danger of collapse, so any false move could cause an accident, to workers and the structure.
Plainly said, the shores are there leaning against the building, nice and snug, and braced to stop them moving, but they are not used to push the structure in any way.
SHORING IS TO STOP MATTERS GETTING WORSE, BUT NOT TO RECTIFY ANY PROBLEMS.

When I was a young guy in Northern England I lived in an area that suffered from subsidence due to coal mining. The sketch above is how we used to shore up houses that had started to give at the seams.
The main point to take from this sketch is the the raker and the wall plate do not just sit there under their own weight. They have to be fixed to the wall, and a couple of masonry anchors will not do it. The method commonly used was to put a needle into the brickwork and a cleat to stop it moving.

The single raker was OK but far more often we used a double raking shore, even on only two story buildings.
For more on this type of shoring, the setting out etc. go to the next page
For non glossary articles of a general and how to nature go to the formwork section on this site.

Shore Type

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Flying shore
Dead shore
Raking shore

Flying Shore

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Flying Shore

A horizontal shore between two buildings to give temporary support to one or both of them

These types of shores are only possible of course where the gap between the two buildings is quite small. If they can be used then they do have the advantage of allowing passage under them, whereas raking shore do take up a lot of room.

What is seen here is one main shore and two sets of raking struts that are providing support for three floors in each of the buildings

The details of the joints and needles etc are similar to the those on the raking shore details

For non glossary articles of a general and how to nature go to the formwork section on this site.

Above is a shot of a building site that has already had the existing building demolished, and the two adjacent building are braced off each other with purpose made triangular steel beams.

At the right is a rather poor shot of the end of one of the beams. It can just about be seen that it has a sturdy end to it that has screw jacks fitted to each leg. Both ends of the beam have the same treatment.

As is normal to all propping and shoring work the end steel plates of the shores are pushing against timber pieces, partly to spread the load but also to give a cushioning effect. NEVER PLACE TEMPORY STEEL PROPS DIRECTLY AGAINST MASONRY OF CONCRETE. They can and they do slip.

Note! As in all these shoring examples, the shores are lined up with floors of the building that they are supporting.

In case you are curious about the stuff hanging off the shoring, the shot was taken in Paris and a nearbye gallery owner or artist has hung a few painting off them.

General Obligations

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Setting out (principal datum)
Site boundary
Safety regulations by Labour Department
Protection of roads and adjacent land
Shoring types

Construction Cost

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Building type
Labor
Materials
Location
Others: e.g. geotechnical cost

Fire Code

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a. dividing into compartments
b. adequate resistance to the spread of fire and smoke
by separation of different uses in the building;
by compartment walls and floors
and by separation from any adjoining building or site
c. maintain the stability of the building in case of fire
d. adequate resistance to the spread of fire over the roof

Critical Path Method (CPM)

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History

The critical path method (CPM) is a project modeling technique developed in the late 1950s by Morgan R. Walker of DuPont and James E. Kelley, Jr. of Remington Rand.^[2] Kelley and Walker related their memories of the development of CPM in 1989.^[3] Kelley attributed the term "critical path" to the developers of the Program Evaluation and Review Technique which was developed at about the same time by Booz Allen Hamilton and the US Navy.^[4] The precursors of what came to be known as Critical Path were developed and put into practice by DuPont between 1940 and 1943 and contributed to the success of the Manhattan Project.^[5]

CPM is commonly used with all forms of projects, including construction, aerospace and defense, software development, research projects, product development, engineering, and plant maintenance, among others. Any project with interdependent activities can apply this method of mathematical analysis. Although the original CPM program and approach is no longer used, the term is generally applied to any approach used to analyze a project network logic diagram.

[edit]Basic technique

The essential technique for using CPM ^[6] is to construct a model of the project that includes the following:

A list of all activities required to complete the project (typically categorized within a work breakdown structure),
The time (duration) that each activity will take to completion, and
The dependencies between the activities.

Using these values, CPM calculates the longest path of planned activities to the end of the project, and the earliest and latest that each activity can start and finish without making the project longer. This process determines which activities are "critical" (i.e., on the longest path) and which have "total float" (i.e., can be delayed without making the project longer). In project management, a critical path is the sequence of project network activities which add up to the longest overall duration. This determines the shortest time possible to complete the project. Any delay of an activity on the critical path directly impacts the planned project completion date (i.e. there is no float on the critical path). A project can have several, parallel, near critical paths. An additional parallel path through the network with the total durations shorter than the critical path is called a sub-critical or non-critical path.

Although the activity-on-arrow diagram ("PERT Chart") is still used in a few places, it has generally been superseded by the activity-on-node diagram, where each activity is shown as a box or node and the arrows represent the logical relationships going from predecessor to successor as shown in the diagram Activity-on-node diagram showing critical path schedule, along with total float and critical path drag computations.

Activity-on-node diagram showing critical path schedule, along with total float and critical path drag computations

In this diagram, Activities A, B, C, D, and E comprise the critical or longest path, while Activities F, G, and H are off the critical path with floats of 10 days, 5 days, and 20 days respectively. Whereas activities that are off the critical path have float and are therefore not delaying completion of the project, those on the critical path will usually have critical path drag 7, i.e., they delay project completion. The drag of a critical path activity can be computed using the following formula:

1. If a critical path activity has nothing in parallel, its drag is equal to its duration. Thus A and E have drags of 10 days and 20 days respectively. 2. If a critical path activity has another activity in parallel, its drag is equal to whichever is less: its duration or the total float of the parallel activity with the least total float. Thus since B and C are both parallel to F (float of 15) and H (float of 20), B has a duration of 20 and drag of 15 (equal to F's float), while C has a duration of only 5 days and thus drag of only 5. Activity D, with a duration of 10 days, is parallel to G (float of 5) and H (float of 20) and therefore its drag is equal to 5, the float of G.

These results, including the drag computations, allow managers to prioritize activities for the effective management of project completion, and to shorten the planned critical path of a project by pruning critical path activities, by "fast tracking" (i.e., performing more activities in parallel), and/or by "crashing the critical path" (i.e., shortening the durations of critical path activities by adding resources).

[edit]Expansion

Originally, the critical path method considered only logical dependencies between terminal elements. Since then, it has been expanded to allow for the inclusion of resources related to each activity, through processes called activity-based resource assignments and resource leveling. A resource-leveled schedule may include delays due to resource bottlenecks (i.e., unavailability of a resource at the required time), and may cause a previously shorter path to become the longest or most "resource critical" path. A related concept is called the critical chain, which attempts to protect activity and project durations from unforeseen delays due to resource constraints.

Since project schedules change on a regular basis, CPM allows continuous monitoring of the schedule, allows the project manager to track the critical activities, and alerts the project manager to the possibility that non-critical activities may be delayed beyond their total float, thus creating a new critical path and delaying project completion. In addition, the method can easily incorporate the concepts of stochastic predictions, using the Program Evaluation and Review Technique (PERT) and event chain methodology.

Currently, there are several software solutions available in industry that use the CPM method of scheduling, see list of project management software. The method currently used by most project management software is based on a manual calculation approach developed by Fondahl of Stanford University.

[edit]Flexibility

A schedule generated using critical path techniques often is not realised precisely, as estimations are used to calculate times: if one mistake is made, the results of the analysis may change. This could cause an upset in the implementation of a project if the estimates are blindly believed, and if changes are not addressed promptly. However, the structure of critical path analysis is such that the variance from the original schedule caused by any change can be measured, and its impact either ameliorated or adjusted for. Indeed, an important element of project postmortem analysis is the As Built Critical Path (ABCP), which analyzes the specific causes and impacts of changes between the planned schedule and eventual schedule as actually implemented.

from
http://en.wikipedia.org/wiki/Critical_path_method

What is Float Time, and Who Owns It?

2011-10-12T05:55:00.001-07:00

South Carolina Construction Law - Discussion of mechanic's liens, delay claims, coverage, and constr: What is Float Time, and Who Owns It?

What is Float Time, and Who Owns It?

Float Time is the period in Critical Path Method scheduling that allows the contractor to an excusable delay when the original contract schedule allows more than enough time to perform the work. In other words, the float is the maximum delay allowed before a delay will cause a slow-down in completion of the whole project.

Ownership of the float is important when the project becomes delayed and a determination must be made as to who is responsible for the delay. The owner must also be known to calculate the length of the delay and whether the contractor should be given extra time to complete the work.

If the site owner owns the float, then it can require the contractor to perform additional work outside of the critical path, without extending the original contract deadline and without paying additional money to the contractor. If the contractor owns the float then any additional work assigned that is not on the critical path could result in an extension to the completion date. If the contractor is considered owner of the float it could be considered the property of all contractors and therefore open to be used by any contractor on the job.

The majority view is that the first party to use the float is considered the owner of the float, but some insiders suggest that if the contract doesn’t specify the owner of the float, that it should belong to the contractor because it should have the authority to control its own work and schedule.

Private Sector Contracts

A dispute arose in Construction Enterprises & Contractors, Inc. v. Orting School Dist. No. 344, 2004 Wash. App. Lexis 681 (2004), when CE&C encountered in the water, sewer, and storm plans and the road grading and paving plans while working on elementary school. Even though CE&C completed the job on time, they sued the school district for losses resulting from inadequate design and failure to provide timely fixes for the design deficiencies. CE&C also sued Warner Engineering, the designer of the paving, grading, water, sewer, and storm plans. Warner used the float as a defense and claimed that the contract between the district and CE&C stated the float was owned by the district and therefore CE&C was not entitled to any additional payment by reason of loss or use of any float time because they still finished the job before the completion date. However, this decision was reversed because the contract did not provide a definition for float time. Therefore, the appeals court ruled the term was ambiguous and was not properly understood. In conclusion float time should be properly defined concerning damages regarding disruption as opposed to delay.

Public Sector Contracts

Some states specifically state which party owns the float in state contracts. For example, California’s Department of Transportation explicitly stated that the float belonged to the contractor. This successful implementation gave contractors an incentive finish the job quickly. Federal contracts however state the float is not for exclusive use by either party. However, the contracts state the government will allow an extension for performance required under certain clauses, but only to the extent that these time adjustments do not exceed total float on the paths involved. If a contractor wants an adjustment based on government changes then they must show the change affected completion of the overall project and the extent to which the project was delayed (Maron Construction Co., Inc. GSBCA No. 13625 (April 7, 1998.)) InMaron, the contract stated that the government was not responsible for any delay or overhead increases incurred by Maron if the time could be absorbed by the total float time. The Board ruled that the government can preclude its liability for delay damages, but they must specifically and expressly exempt themselves from liability, which this contract did not. In conclusion, there should be no assumptions about float time and contracts should specifically define the float, the owner of the float, and explain the intent regarding the calculation of damages for delays arising out of a dispute.

This site and any information contained herein is intended for informational purposes only and should not be construed as legal advice. Seek a competent attorney for advice on any legal matter.

from
http://southcarolinaconstructionlawyer.com/2008/06/28/what-is-float-time-and-who-owns-it.aspx

Construction Speed

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Contractor's programme
Critical path
Float time
Concrete cycle