structural engineering

WELDING PERFORMANCE QUALIFICATION TEST (WPQ)

2021-02-08T03:23:00.035-08:00

A Welder Performance Qualification (WPQ) is a test certificate that shows whether a welder possesses the necessary experience and knowledge to perform the specifications of a particular weld procedure.

The scope of the WPQ test varies depending on the weld procedure, but it generally involves non-destructive and destructive testing. To completed this procedure, the need of staff required includes chemists, engineers and NDT inspectors. The on-site, full-service machine shop can prepare any size weld coupon for testing. After passing required tests, they will issue you a qualification certificate.

Some of the Welder Performance Qualification (WPQ) / Welding Qualification Test Reord (WQTR) form after completed welding test is shown below:

Steel - Storage and Handling

2020-04-01T07:56:00.000-07:00

Hello..

Generally, greater care is required in storing and handling stainless steel than carbon steel to avoid damaging the surface finish (especially for bright annealed or polished finishes) and to avoid contamination by carbon steel and iron.

Storage and handling procedures should be agreed between the relevant parties to the contract in advance of any fabrication and in sufficient detail to accommodate any special requirements. The procedures should cover, for instance, the following items:

The steel should be inspected immediately after delivery for any surface damage.
The steel may have a protective plastic or other coating. This should be left on as long as possible, removing it just before final fabrication. The protective covering should be called for in the procurement document if it is required (e.g. for bright annealed finishes).
Storage in salt-laden humid atmospheres should be avoided. Storage racks should not have carbon steel rubbing surfaces and should, therefore, be protected by wooden, rubber or plastic battens or sheaths. Sheets and plates should preferably be stacked vertically; horizontally stacked sheets may get walked on with a risk of iron contamination and surface damage.
Carbon steel lifting tackle, e.g. chains, hooks, and cleats should be avoided. Again, the use of isolating materials, or the use of suction cups, will prevent iron pick-up. The forks of fork lift trucks should also be protected.
Contact with chemicals including undue amounts of oils and greases (which may stain some finishes) should be avoided.
Ideally, segregated fabrication areas for carbon steel and stainless steel should be used. Only tools dedicated to stainless steel should be employed (this particularly applies to grinding wheels and wire brushes). Note that wire brushes and wire wool should be of stainless steel and generally in a grade that is equivalent in terms of corrosion resistance (e.g. do not use ferritic stainless steel brushes on austenitic stainless steel).
As a precaution during fabrication and erection, it is advisable to ensure that any sharp burrs formed during shearing operations are removed.
Consideration should be given to any requirements needed in protecting the finished fabrication during transportation.

Thats all for today..see u next articles.

How To Calculate Shear Forces On Bolts Connection Joints

2020-03-29T07:43:00.000-07:00

How to determine shear forces on bolts?

Here's below shows one of the simple shear forces calculation of bolts connection joints when received Mxx = 46.223 kN/M of maximum bending moment.

Mxx = M dead + M live
= 16.147 + 30.076
= 46.223 kN/M

Flexible Pavement Design

2020-03-18T02:15:00.001-07:00

Flexible Pavement Design

Design Procedure of IRC

Design Approach and Criteria - The following three types of pavement distress resulting from repeated application of traffic are considered:

(i) Horizontal tensile strain at the bottom of the bituminous layer
(ii) Vertical compressive strain at the top of the subgrade
(iii) Pavement deformation with in the bituminous layer

The deformation with in the bituminous layer is assumed to be controlled by meeting the mix design requirements

Failure Criteria

1. Fatigue Cracking

Is due to the build up of tensile strain at the bottom of Asphaltic Concrete Layer
Pavement is considered failed if 20% of the surface has cracked

2. Rutting Failure

Is due to the build up of excessive compressive strain at the top of subgrade layer
Pavement is considered failed if it exhibits a rut depth of 20 mm.

IRC Design Approach and Criteria

The pavement has been modeled as a three layer structure and stresses and strains at

critical locations have been computed using the linear elastic structural model FPAVE.

Nondestructive Testing with Bruker Handheld XRF Analyzers

2017-10-27T08:46:00.000-07:00

Non-destructive testing or NDT – also called non destructive examination (NDE), nondestructive inspection (NDI), and non-destructive evaluation (NDE) – with Bruker handheld XRF analyzers can be achieved in seconds or minutes for a broad variety of applications. By contrast, other elemental analysis techniques, such as OES (Optical Emission Spectrometry) leave a spark mark on the alloys being analyzed; and ICP (Inductively Coupled Plasma) analysis or AA (Atomic Absorption) analysis are destructive to the sample. Handheld XRF allows you to perform completely nondestructive testing on practically any material.

When it is crucial that materials not be marred in any way yet elemental analysis is required, nondestructive testing with handheld XRF guns make it possible for many manufacturers, retailers, distributors and consultants to remain compliant with regulations:

Art Conservation and Restoration
Consumer Products/H.R.4040 with the (S1 TITAN) XRF Gun
Lead in Apparel with the S1 TITAN
TPCH- Toxics in Packaging Clearing House Laws
ASTM F-963 - The Mandatory Toy Standard
RoHS- Restriction of Hazardous Substances
Prop 65- Lead restricted from all products sold in CA
Jewelry Evaluation - Precious Metals, Gold, Silver
PMI Analysis
Positive Materials Identification in Aerospace Alloys
QA/QC for Alloys

There are also applications in industries where nondestructive testing is not required yet it makes life a lot easier if the sample is not destroyed and can be confirmed with back up analysis in a laboratory:

Soil Remediation
Mining Exploration

Whether you are striving to comply with regulations or conducting elemental analysis where nondestructive testing is necessary for optimum efficiency, handheld XRF analyzers from Bruker can get the job done, quickly, effectively and nondestructively.

Analysis and Design of the Fastener

2015-07-11T03:34:00.001-07:00

Analysis and retrofitting design of the fastener group for the spreader

bar of SM3 disassembly

Background:

Try to re-use (or to modify) the existing Mino project spreader bar for SM3

disassembly project. the capacity of the spreader bar for SM3 project is:

Overall load P_t = 9.4 tons with span distance L_s = 201 in

Applicable codes:

ASME B30.20; “Below – the – Hook Lifting Devices”

ASD, AISC 9^th edition

References:

ME – 397459

ME – 397426

MD – 397452

“Steel Structures Design and Behavior” by C. Salmon & J. Johnson, 3^rd edition

Assumptions:

Slip critical connection, single shear

Figure 1 of page 1 is showing that when the applying load P is eccentric to the centroid of the bolt group, this physical configuration is the actual design of the spread bar using for sm3 project.

Where:

P = 9,400 lbs, applying load

L = 47.625 in

Location A is the geometrical centroid of the bolt group, 6 bolts are located as

showing in Figure 1. currently, it is assuming: A325, ¾ - 10, UNC

n = 6

per Table I –D, part 4 of ASD, R_av = 7.51 kip (allowable shear load)

Find out the local properties of the fastener group:

∑x² = 4 (4)² = 64 in²

∑y²= 6 (2)² = 24 in²

∑x²+ ∑y²= 88 in²

The primary shear load R_vof each bolt subject to the applying load P:

R_v = P/n = 9,400 lbs / 6

= 1,567 lbs ↓

The secondary torsional shear load of the bolt subject to the moment PL:

To pick the bolt of the most right top one as showing in figure 1,

Where: R_x = PLy ÷ (∑x²+ ∑y²)

= (9,400 lbs) x (47.625 in) x (2 in) ÷ 88 in²

= 10,174 lbs. →

R_y = PLx ÷ (∑x²+ ∑y²)

= (9,400 lbs) x (47.625 in) x (4 in) ÷ 88 in²

= 20,349 lbs ↓

The resultant force applying to the most right top bolt:

R = [(R_v+ R_y)² + R_x²]^1/2

= [(1,567+ 20,349)² + (10,174)²]^1/2 lbs

= 23,259 lbs > R_av = 7.51 kip

It is necessary to look for:

a. Different specifications of the fastener with the same fastener group.

b. Another pattern of the fastener group

A.Different specification of the fastener with the same fastener group:

A1. If using 6 bolts with A325, 1 3/8”- 6 UNC,*

then R_av = 25.2 ksi > R = 23.26 ksi,

*: The hole ctr. to hole ctr. distance L_e = 4.0 in < 3d = 4.13 in

A2. If using same fastener group with bolt of A490, 1 ¼”- 7, UNC,

then R_av = 25.8 ksi > R = 23.26 ksi (per Table I-D, part 4 of ASD, 9^th edition)

where: L_e = 4.0 in > 3d = 3.75 in

B. Modify the current pattern of the fastener group:

Figure 2 on page 3 is the new fastener group with adding additional 10 fasteners to

the original group, it can be found the new properties of the fastener group:

∑x² = (4 (4)² + 4 (2)² + 6 (6)²) in²

= (64 + 16 + 216) in²

= 296 in²

∑y²= (6(2)² + 8(3.375)²) in²

= 115 in²

∑x²+ ∑y²= (296 + 115) in²

= 411 in²

Also n = 16

The primary shear load R_vof each bolt subject to the applying load P:

R_v = P/n = 9,400 lbs / 16

= 588 lbs ↓

The secondary torsional shear load of the bolt subject to the moment PL,

To pick the bolt of the most right top one as denoted as bolt A of Figure 2:

Where: R_x = PLy ÷ (∑x²+ ∑y²)

= (9,400 lbs) x (47.625 in) x (3.375 in) ÷ 411 in²

= 3,677 lbs. →

R_y = PLx ÷ (∑x²+ ∑y²)

= (9,400 lbs) x (47.625 in) x (6 in) ÷ 411 in²

= 6,536 lbs ↓

The resultant force R applying to the most right top bolt A:

R = [(R_v+ R_y)² + R_x²]^1/2

= [(588+ 6,536)² + (3,677)²]^1/2 lbs

= 8,017 lbs > R_av = 7.51 kip

If the bolt material change to ASTM A490, then R_av = 9.28 kip

R = 8.017 kip < R_av = 9.28 kip

Since only 2 bolts of the fastener group will experience shear load of R ~ 8.017 kip, all the rest bolt shear load is less than 7.51 kip, so there are two choices:

1. The most top right and bottom right bolts use A490, the rest bolts use A325. (3/4 – 10, UNC.)

2. Or all of them use A490 bolts (3/4 – 10, UNC)

The conclusions:

There are two ways to modify the current fastener group to meet the new design criteria of spreader bar for SM3 disassembly:

1. Using (6) A490 high strength structural bolts with spec. of 1¼ - 7, UNC (original is ¾ -10, UNC), or

2. Using (16) A490 high strength structural bolts with spec. of ¾ -10, UNC.

Determine the Operating Group of the Hoist

2014-05-03T09:50:00.000-07:00

General Comparison

Summarizing

To select correct crane duty, crane structure and mechanical components, the user must identify and pass on the following information to the supplier:

Average lifts and trolley and bridge movements made in an hour.
Average length of each movement.
Estimate the load lifted each time.
Total operating hour per day.

FEM SERVICE CLASS

2014-04-23T09:37:00.000-07:00

To determine your crane duty group (according to FEM, Fédération Européene de la Manutention) you need following factors:

1) Load spectrum (Indicates the frequency of maximum and smaller loadings during examined time
period).

2) Class of utilization (This is determined according to number of hoisting cycles during lifetime of crane)

3) Combining these factors is how a duty group is selected.

Example of different load spectrums:

Calculate the Average Daily Operating Time

t = (2 x H x N x T) / (V x 60)

Where:

H = average hoisting height (m or feet)
N = number of work cycles per hour (cycle/hour)
T = daily working time (h)
V = hoisting speed (m/min or feet/min)

AISE SERVICE CLASS

2014-04-08T09:27:00.000-07:00

AISE also provides for different service classes for cranes covered under AISE Technical Report No. 6, "Specifications for Electric Overhead Traveling Cranes for Steel Mill Service". Like CMAA, AISE also provides a numerical method for determining crane class based on the expected load spectrum. Without getting into the specifics of this method, AISE does generally describe the different service classes (load cycles) as follows:

1. Service Class 1 (N1): Less than 100,000 cycles

2. Service Class 2 (N2): 100,000 to 500,000 cycles

3. Service Class 3 (N3): 500,000 to 2,000,000 cycles

4. Service Class 4 (N4): Over 2,000,000 cycles

Further AISE describe the different Load Classes as

1. L1= Cranes which hoist the rated load exceptionally, and normally hoist very light loads

2. L2= Cranes which rarely hoist the rated load, and normally hoist loads about 1/3 the rated capacity

3. L3= Cranes which hoist the rated load fairly frequently, and normally hoist loads between 1/2 and 2/3 or the rated capacity

4. L4= Cranes which are regularly loaded close to the rated capacity

Based on the load classes and load cycles, the CMMA chart below helps determine the class of the crane.

HMI/ASME HOIST DUTY RATINGS

2014-03-20T09:00:00.000-07:00

The following table provides an idea of the relative significance of the duty cycle ratings for the various electric hoists. Note that the duty cycle determination for a particular application involves obtaining a significant amount of additional information and expertly applying it to the intended use.

CLASSIFICATION OF CRANES

2014-03-06T08:23:00.000-08:00

Crane Duty Groups

Crane duty groups are set of classifications for defining the use of crane. There are several different
standards where these groups are named differently. One may have heard names CMAA, FEM, ISO or HMI. They all have their own classification of duty groups but are still based on the same calculations and facts. Following is a short description of what a duty group means and what it is for.

A crane duty group tells which kind of duty the crane is for; the range is from light duty up to very heavy duty. It is vital to define the needs and estimate the use because of safety reasons and for to ensure a long working life for the crane. You can't put for example a crane designed for light duty into continuous heavy-duty work.

CMAA Crane Classification

As to the types of cranes covered under CMAA Specification No. 70 (Top Running Bridge and Gantry Type Multiple Girder Electric Overhead Traveling Cranes); there are six (6) different classifications of cranes, each dependent on duty cycle. Within the CMAA Specification is a numerical method for determining exact crane class based on the expected load spectrum. Aside from this method, the different crane classifications, as generally described by CMAA, are as follows:

ESSENTIAL PARAMETERS FOR SPECIFING EOT CRANES - Part 2

2014-02-21T08:15:00.000-08:00

Hello Structural Engineering readers, how are u? Today we continued some more tips about the above topic for your further explanation.

Other than addressing the last post (see here) parameters, some specific conditions applicable to your application must be mentioned.

1) Do you need the use of a second hoist on the bridge crane? (This hoist may be used as an auxiliary hoist or be required in a process such as tilting/tipping. In case you are handling long materials, like steel tubes and plates, the best solution are to have a crane with two hoists (and hooks) for better stability of the load ensuring safe lifting).

2) What will the operating environment be (dust, paint fumes, outdoor, etc.)?

3) Is there existing cranes on the runway? Then, consider the use of a collision avoidance or collision warning system.

4) Do you require a catwalk on the crane for maintenance access?

5) What other accessories are required such as lights, warning horns, weigh scales, limit switches, etc.

Load is defined as the maximum working load suspended under the load hook. Load block and ropes are not included in the rated load.

The design load for the crane system is based on the rated capacity plus 15% for the weight of the hoist and trolley (capacity x 1.15) and an additional 25% for impact (capacity x 1.25) for a total design capacity x 1.4. (Note 25% impact factor is good for hoists speeds up to 50 fpm).

The capacity of crane is the maximum rated load (in tons) which a crane is designed to carry. The net
load includes the weight of possible load attachment. For example , a 1000 lb crane allow you to pick up a 1000lb load, provided the hoist weighs 150lbs or less and the hoist speed is less than 50 feet per minute.

Under no conditions should the crane be loaded beyond its rated capacity.

Note that the Crane test loads are typically specified at 125% of rated capacity by both OSHA and ASME.

ESSENTIAL PARAMETERS FOR SPECIFING EOT CRANES

2014-02-07T08:07:00.000-08:00

Hii readers, today we will show you some tips how to select correct crane envelope that will fit in the building foot print, and the user must identify and pass on the following key information to the supplier before proceed with manufacturing process:

1) Crane Capacity - The rated load, the crane will be required to lift. Rated load shall mean the
maximum load for which a crane or individual hoist is designed and built by the manufacturer and
shown on the equipment identification plate.

2) Lift Height - The rated lift means the distance between the upper and lower elevations of travel of
the load block and arithmetically it is usually the distance between the beam and the floor, minus the
height of the hoist. This dimension is critical in most applications as it determines the height of the
runway from the floor and is dependent on the clear inside height of the building. Do not forget to
include any slings or below the hook devices that would influence this value.

3) Runway Height – The distance between the grade level and the top of the rail.

4) Clearance - The vertical distance between the grade level and the bottom of the crane girder.

5) Clear Span- Distance between columns across the width of the building. Building width is defined as the distance from outside of eave strut of one sidewall to outside of eave strut of the opposite
sidewall. Crane Span is the horizontal center distance between the rails of the runway on which the
crane is to travel. Typically distance is approximate to 500mm less than the width of the building.
How much span a crane requires depends on the crane coverage width dictated by the application.
(According to the span and the maximum load handling capacity, the crane steel structure is
selected to be either a single or double girder crane construction).

6) Building Height - Building height is the eave height which usually is the distance from the bottom of the main frame column base plate to the top outer point of the eave strut. Eave height is the
distance from the finished floor to the top outer point of the eave strut. There must be a safety
distance between the top edge of the crane runway rail and the first obstacle edge in the building
(for example roof beams, lights and pipes).

7) Runway Length- The longitudinal run of the runway rail parallel to the length of the building.

8) Hook approaches - Maximum hook approach is the distance from the wall to the nearest possible
position of the hook. The smaller the distance is, the better can the floor area be utilized. Always
check which crane gives optimum hook approaches and when combined with the true lift of the hoist
you can utilize most of the available floor space. This is also termed as side hook approach.
End Approach – This term describes the minimum horizontal distance, parallel to the runway,
between the outermost extremities of the crane and the centerline of the hook.

9) Bridge, Trolley and Lift Speeds - The rate at which the bridge or trolley travels or at which the hoist lifts is usually specified in feet per minute or FPM. The crane operating speeds are selected to allow safe operation whilst using the pendant. Dual operating speeds, normally a fast and slow speed with a ratio of 4:1 are commonly used but for optimum control a variable speed control system is strongly recommended.

10) Electrical Requirements - Specify the circuit voltage shall not exceed 600 volts for AC or DC current. Ideally 480 volt, 3 phase, 60 hertz for US requirements. The runway power is usually by conductor bar and hoisting trolley by festoon cable. (refer section 6 for details)

11) Control Requirements - The control circuit voltage at pendant pushbuttons shall not exceed 150
volts for AC and 300 volts for DC. Other control options including radio control, free-floating pendant (festooned) or hoist-mounted pendant requirements must be stated.

Ok, thats all for today. We will learn some more in next post. Thank you for reading.

SPECIFYING AN OVERHEAD CRANE

2014-01-29T23:26:00.000-08:00

Specifying an overhead crane. This is generally structural layout where overhead crane is located in building.

BASIC CRANE COMPONENTS

2014-01-15T23:14:00.000-08:00

To help you and the reader better understand names and expressions used throughout this course, find below is a diagram of basic crane components.

1) Bridge - The main traveling structure of the crane which spans the width of the bay and travels in a direction parallel to the runway. The bridge consists of two end trucks and one or two bridge girders depending on the equipment type. The bridge also supports the trolley and hoisting mechanism for up and down lifting of load.

2) End trucks - Located on either side of the bridge, the end trucks house the wheels on which the entire crane travels. It is an assembly consisting of structural members, wheels, bearings, axles, etc., which supports the bridge girder(s) or the trolley cross member(s).

3) Bridge Girder(s) - The principal horizontal beam of the crane bridge which supports the trolley and is supported by the end trucks.

4) Runway - The rails, beams, brackets and framework on which the crane operates.

5) Runway Rail - The rail supported by the runway beams on which the crane travels.

6) Hoist - The hoist mechanism is a unit consisting of a motor drive, coupling, brakes, gearing, drum, ropes, and load block designed to raise, hold and lower the maximum rated load. Hoist mechanism is mounted to the trolley.

7) Trolley - The unit carrying the hoisting mechanism which travels on the bridge rails in a direction at right angles to the crane runway. Trolley frame is the basic structure of the trolley on which are mounted the hoisting and traversing mechanisms.

8) Bumper (Buffer) - An energy absorbing device for reducing impact when a moving crane or trolley reaches the end of its permitted travel, or when two moving cranes or trolleys come into contact. This device may be attached to the bridge, trolley or runway stop.

EOT CRANE CONFIGURATION

2014-01-01T23:10:00.000-08:00

Today's post is to know electric overhead travelling crane configuration.

1) Under Running (U/R)
2) Top Running (T/R)

Under running cranes

Under Running or under slung cranes are distinguished by the fact that they are supported from the roof structure and run on the bottom flange of runway girders. Under running cranes are typically available in standard capacities up to 10 tons (special configurations up to 25 tons and over 90 ft spans). Under hung cranes offer excellent side approaches, close headroom and can be supported on runways hung from existing building members if adequate.

The Under Running Crane offers the following advantages:

o Very small trolley approach dimensions meaning maximum utilization of the building's width and height.
o The possibility of using the existing ceiling girder for securing the crane track.

Following are some limitations to Under Running Cranes:-

o Hook Height - Due to Location of the runway beams, Hook Height is reduced
o Roof Load - The load being applied to the roof is greater than that of a top running crane
o Lower Flange Loading of runway beams require careful sizing otherwise, you can "peel" the flanges off the beam

Top Running Cranes

The crane bridge travels on top of rails mounted on a runway beam supported by either the building columns or columns specifically engineered for the crane. Top Running Cranes are the most common form of crane design where the crane loads are transmitted to the building columns or free standing structure. These cranes have an advantage of minimum headroom / maximum height of lift.

Which Crane should you choose – Single Girder or Double Girder?

2013-12-18T23:00:00.000-08:00

Hii..this post is about which crane should you choose either Single Girder or Double Girder?

A common misconception is that double girder cranes are more durable! Per the industry standards (CMMA/DIN/FEM), both single and double girder cranes are equally rigid, strong and durable. This is because single girder cranes use much stronger girders than double girder cranes. The difference between single and double girder cranes is the effective lifting height.

Generally, double girder cranes provide better lifting height. Single girder cranes cost less in many ways, only one cross girder is required, trolley is simpler, installation is quicker and runway beams cost less due to the lighter crane dead weight. The building costs are also lower. However, not every crane can be a single girder crane. Generally, if the crane is more than 15 ton or the span is more than 30m, a double girder crane is a better solution.

The advantages and limitations of Single / double girder cranes are as follows:

Single Girder Cranes

o Single girder bridge cranes generally have a maximum span between 20 and 50 feet with a
maximum lift of 15-50 feet.
o They can handle 1-15 tonnes with bridge speeds approaching a maximum of 200 feet per minute (fpm), trolley speeds of approximately 100 fpm, and hoist speeds ranging from 10-60 fpm.
o They are candidates for light to moderate service and are cost effective for use as a standby (infrequently used) crane.
o Single girder cranes reduce the total crane cost on crane components, runway structure and building.

Double Girder Cranes

o Double girder cranes are faster, with maximum bridge speeds, trolley speeds and hoist speeds approaching 350 fpm, 150 fpm, and 60 fpm, respectively.
o They are useful cranes for a variety of usage levels ranging from infrequent, intermittent use to continuous severe service. They can lift up to 100 tons.
o These can be utilized at any capacity where extremely high hook lift is required because the hook can be pulled up between the girders.
o They are also highly suitable where the crane needs to be fitted with walkways, crane lights, cabs, magnet cable reels or other special equipment.

TYPES OF ELECTRIC OVERHEAD CRANES - Part 2

2013-12-04T22:57:00.000-08:00

Hii...we continued the last post that talk about overhead crane generally or basically..

There are various types of overhead cranes with many being highly specialized, but the great majority of installations fall into one of three categories:

a) Top running single girder bridge cranes,
b) Top running double girder bridge cranes and
c) Under-running single girder bridge cranes.

Electric Overhead Traveling (EOT) Cranes come in various types:

1) Single girder cranes - The crane consists of a single bridge girder supported on two end trucks. It has a trolley hoist mechanism that runs on the bottom flange of the bridge girder.

2) Double Girder Bridge Cranes - The crane consists of two bridge girders supported on two end trucks. The trolley runs on rails on the top of the bridge girders.

3) Gantry Cranes - These cranes are essentially the same as the regular overhead cranes except that the bridge for carrying the trolley or trolleys is rigidly supported on two or more legs running on fixed rails or other runway. These “legs” eliminate the supporting runway and column system and connect to end trucks which run on a rail either embedded in, or laid on top of, the floor.

4) Monorail - For some applications such as production assembly line or service line, only a trolley hoist is required. The hoisting mechanism is similar to a single girder crane with a difference that the crane doesn’t have a movable bridge and the hoistingtrolley runs on a fixed girder. Monorail beams are usually I-beams (tapered beam flanges).

Ortie, see u next post..thanks.

General Overview - Overhead Crane Part 1

2013-11-20T20:45:00.005-08:00

Cranes are industrial machines that are mainly used for materials movements in construction sites, production halls, assembly lines, storage areas, power stations and similar places. Their design features vary widely according to their major operational specifications such as: type of motion of the crane structure, weight and type of the load, location of the crane, geometric features, operating regimes and environmental conditions.

When selecting an electric overhead traveling crane, there are a number of requirements to be taken into account.

1) What specifications, codes or local regulations are applicable?
2) What crane capacity is required?
3) What is the required span?
4) What is the lift required by the hoist?
5) What will be the duty cycle (usage) of the crane?
6) What is the hoist weight? Do you need the use of a second hoist on the bridge crane?
7) What is the hook approach required?
8) What length of runway system is desired?
9) What factors need to be considered in the design of runway and building structure?
10) What will the operating environment be (dust, paint fumes, outdoor, etc)?
11) What are the necessary crane and trolley speeds?
12) What is the supply voltage/phases/amperage?
13) What control system is desired?
14) Is there existing cranes on the runway?

15) What safety considerations are to be followed?

16) Consider maintenance aspects of the crane.

17) Consider other accessories such as lights, warning horns, weigh scales, limit switches, etc.

But before we discuss further, you have need to know a general clarity of the terminology used in the overhead crane industry.

Ok..wait for the next post..see you!!

Factors To Consider When Purchasing A Crane 2010

2010-10-23T01:13:00.000-07:00

Hello to my readers..

If you own a business in one of these industries, the choice of a crane is critical for the success and efficiency of your business. So, here are some important factors that you must take into account for buying a crane.

Types of Crane

To begin with, you must know the different types of cranes available in the market. You must decide whether you need a mobile or fixed crane. You must also learn about overhead cranes, gantry cranes, monorail cranes, material lifting cranes, heavy duty cranes and other options to decide which one suits your requirements.

Lifting Capacity

An important consideration while choosing a crane is the maximum weight lifting capacity specified by the manufacturer. Different applications require materials with different weights to be lifted. So, the crane you select must be capable of supporting the maximum weight to be lifted at your workplace. Make sure that you dont oversize the capacity of the crane purchased.

Usage Limit

Another deciding factor to buy one of the industrial cranes is the limit of its usage. You must know how many times the crane would be used per hour or per shift. Besides, you must also know the shifts per day and the days per week for which the crane would be used. This should help you choose the crane that withstands a particular usage limit.

Learn about Components

Cranes with different components are suitable for different working environments. So, you must take into account the components like mechanical components and electrical components. Besides, you must also learn about the motor controls and operator controls to ensure that the right crane is purchased.

Speeds and Distances

Learn about the speed with which the crane lifts a particular quantity of eight. At the same time, you must learn about the maximum height or horizontal distance that the crane can move. All these factors help you choose the suitable industrial cranes that add efficiency to your working style.

Maintenance Required

Finally, you must consider the maintenance required for different parts of the crane, including motors, gearboxes, bearings, wire ropes and so on. Ask for warranty from the seller of industrial cranes.

Taking all these things into consideration should help you invest money in right types of gantry cranes, heavy duty cranes or other cranes.

Ok, thats all for this post..
See u next post..

Avoiding Pitfalls In Crane Projects

2010-08-29T06:25:00.000-07:00

You have a shiny new building with a shiny new crane and everything looks great. For some reason, though, the crane won’t clear the building columns, even though the contractor and the crane manufacturer are saying everything is to spec and it’s not their problem. Common sense says somebody is wrong and that somebody should have to pay (because it’s going to cost a bundle). Unfortunately in this case, there’s a giant crack in the building specs, and you’ve just fallen through it. This means that after all the arguing and legal costs, you’re still going to have to pay to get it fixed. If you’ve already fallen in this black hole, there’s not much you can do, but if you are about to embark on a new building with an overhead crane, this article will show you where the cracks are and suggest how to bridge them safely.

What Is Required?

The runway alignment specs—written by the Crane Manufacturers Association of America (CMAA) and adopted by the Metal Building Manufacturers Association (MBMA), the American Institute of Steel Construction (AISC), and the Association of Iron and Steel Engineers (AISE)— fill an entire page and take considerable time to interpret. A simplistic summary is that runways must be ±1⁄4 inch in a single bay and no more than ±3⁄8 inch over the full length of the runway.
These tolerances must be maintained in four ways: left/right, up/down, parallel to each other, and level in respect to each other. Figure 1 shows an actual AISC/ CMAA chart.

A second set of crane-related numbers to remember are the crane-to-building tolerances. CMAA and the Occupational Safety and Health Administration (OSHA) require that all moving
objects (the crane and hoist) must clear all stationary objects (the building) horizontally by 2 inches and clear all vertical objects (roof trusses, lights, pipes, etc.) by 3 inches. Although this meets the legal requirements, this author highly recommends the horizontal be increased to
4 inches and the vertical to 6 inches to allow for unforeseen problems.

Where’s the Villain?

As in a detective story, the first move is to round up the suspects. The problem can be found
in one of four areas:
1. Mill steel tolerances
2. Building steel fabrication tolerances
3. Building erection tolerances
4. Overhead crane runway tolerances (measuring and verification methods)

One big problem is that runways usually are built with building steel (wide flanges), fabricated
by building steel fabricators, and installed by building steel erectors, but runway steel is not building steel. In fact, building steel and runway steel are incompatible in the first three ways listed previously. Following is an illustration of just the first point—mill steel tolerances—but the other two items exhibit similar shortcomings. The mill tolerance for structural wide-flange
beams basically is 1⁄8 inch per 10 feet of length, although this oversimplifies the American
National Standards Institute (ANSI)/AISC specification somewhat (see Figure 2).

Therefore, in a common 30-foot bay, the wide-flange beam can have a sweep (horizontal bow) of 3⁄8 inch, which means that putting up this first piece of steel exceeds the acceptable CMAA/MBMA/AISC
runway tolerance already. To compound the problem, the opposing runway can have an equal (but opposite) sweep, doubling the problem.

Solutions

How should this seemingly simple problem be addressed? Three potential solutions exist:
1. Adjust the rail laterally in relation to the girder. Although this solution is the most commonly used, it is bad engineering practice and actually is prohibited by the AISC specifications.
The runway beam/girder is the wide-flange structural shape that supports the runway, while the rail (commonly American Society of Civil Engineers (ASCE) rail, similar to railroad rail) is the track upon which the end truck wheels traverse (see Figure 3). It is a common misconception that the runway beams have no particular installation tolerance and that only the rail is at issue. Further, this assumption seems to be confirmed by the lateral adjustment of the rail fasteners (for example, Jbolts/ hook bolts or patented clips). Actually, the tolerance of the beam installation is governed by the tolerance of the rail installation. This is because, according to AISC Design Guide 7, paragraph 19a, the centerline of the rail should be within ±3⁄4 inch of the girder web thickness. This prevents top flange rollover and subsequent fillet cracking and possibly girder failure.

This conventional wisdom is so commonly accepted that it has evolved into generally accepted practice. Unfortunately, like so much conventional wisdom, it’s wrong, it’s bad for the equipment, it will result in significantly shorter service life, and it can be dangerous.

2. Augment the specs. Just because the generally accepted specs have left the crane runways as an orphan does not mean that you as a prospective new building owner should not include a stop-gap page of specs to cover yourself. If you buy the steel from the same vendor, fabricate
with the same fabricator, and install with the same installation crew, you very likely will end up with the same problem. It defies reason that any efficient contractor can buy, fabricate, and install 20+ pieces of apparently identical red primed steel to a tolerance two to four times tighter than the other several thousand pieces of red steel in that same building. This is not meant to slight building contractors.
Successful contractors have set up a well-disciplined system to produce and install building steel, but runway steel, although similar-looking, is a significantly different animal. While it is unlikely the contractor would adopt this more stringent standard temporarily, it is not impossible.
The silver lining for you, the buyer, in using the augmented specs as part of the contract is that the corrections no longer are your problem or expense.

3. Redefine the scope of building contractor and crane supplier responsibilities. This technically
correct, practically viable solution is the least used of the three, simply because of lack of knowledge and higher up-front costs. The common scope of the crane builder’s contract is to supply and install the crane, runway rail, and conductor bar. This leaves a critical gap in which the buyer is exposed to the previously mentioned problems. The scope should be changed to move responsibility for the runway girders from the building contractor to the
crane builder. Chances are, the crane builder will insist on very tight tolerances from the steel supplier and will take precautions to account for reasonable floor and column tolerances. Also, having the crane builder’s employees install the runways can help to improve installation accuracy because this job is their specialty. If the plant is a union plant, however, the runway conductor bar installation should be awarded to a local electrical contractor, while the crane builder remains responsible for the bar.

Get It Right the First Time

In summary, runway steel is not building steel. Poor runways will result in premature wheel failure, motor and or gearbox failure, and premature runway replacement. With a typical wheel replacement costing $8,000 and new runways costing $50,000 or more, not to mention downtime, getting it right the first time can be a real bargain. Using augmented overhead crane runway specs in conjunction with the information provided here can help you to stay out of court and maintain good relations with valuable vendors.

Overhead Crane - General

2010-08-22T08:43:00.000-07:00

There are many types of overhead cranes, all of which can pose hazards if they are not used properly and with adequate safety precautions. Strict guidelines and safety regulations are published by OSHA (US Department of Labor's Occupational Safety & Health Administration Department). By adhering to these standards and rules, you protect your company from some of the injuries and lawsuits that can be served against companies requiring employees to operate heavy machinery.

Some of OSHA's laws on crane design and manufacture govern the following things.
1-Uniform crane control design and manufacture
2-Trolley and bridge bumper design
3-Stairway and ladder design
4-Trolley and bridge brakes
5-Design and manufacture of electrical components
6-Hoisting equipment design and manufacture

There are several basic types of overhead cranes. OSHA's laws and regulations apply to the following cranes.
1-Cantilever gantry
2-Gantry
3-Semi-gantry
4-Storage bridge
5-Wall

All of these require using the appropriate overhead crane parts for all repairs, as substitutions may result in accidents or defective operation of the machinery.

If you or your employees will be operating cranes and other heavy machinery, here are some safety tips to remember.
1-Cranes should only be used and operated by designated persons.
2-If a crane has been installed since 1971, it must meet all OSHA specifications.
3-An equipment manufacturer or engineer must inspect any crane that has been altered to change its load capacity.
4-You must have a cleared walkway on the side of the crane and above it.
5-You must clearly mark the load capacity of a crane so that everyone who might operate it can see it.
6-If a crane has two or more hoists, you have to clearly mark the load capacity of each hoist so that everyone who might operate it can see it.

Concrete Formwork - Structural Engineer

2010-04-17T04:29:00.000-07:00

The concrete is required to be poured for curing and formation of the desired shape. The general techniques used for formwork are roadform that is a permanent arrangement of shuttering, and timber shuttering that is a customized temporary structure.

Concrete Formwork Basics

Concrete needs to be poured into an enclosed space and remain there until it adequately consolidates to maintain its shape. Concrete that has been poured newly for concrete slabs can be preserved in shape by existing features like walls and edgings. Alternatively, provisional shuttering, which is also called formwork, could be necessary. On vertical structures, formwork construction can be difficult and is therefore usually carried out by professional formwork erectors. However, slab work at ground level is usually less difficult and needs only a simple formwork. In all the cases, whether vertical structures or work at the ground, the formwork should be strong. It must be able to bear the forces produced by the wet concrete, including the weight of the vibration producing equipment. The formwork joints must be fastened adequately and prevent the mix leak during the vibration and curing. The primary formwork types being used for producing ground slabs are steel roadform and customized timber shuttering.

Roadform

Roadform, a permanent type of formwork used for poured concrete for housing and other structures is usually preferred for use since it is strong, capable of bearing different loads, and is a permanent arrangement. It can beconcrete formwork 1 used for construction work at different sites, involves a moderate skill to configure the necessary arrangement, and is inexpensive. It consists of steel sections that are channel-shaped, binding brackets, and an arrangement for the linking of adjacent sections. The units are stacked to create space for the required concrete depth. However, the maximum height is determined by the height of the steel pins that hold the system in its position. The steel pins are located with the bracket and forced into the ground. Each section is aligned accurately and held by tightening the fastening wedge. It is ensured that the roadform is firmly held in its place. Roadform is erected by aligning the sections with a rigid cord and by ensuring that the sections are accurate vertically. The pins should be firm with no gaps between the sections.

Timber Shuttering

Timber shuttering Roadform is only suitable for simple slabs. Timber shuttering, however, may be necessary for complicated work. The enormous benefit of the timber shuttering is that since it is created at the site, it can be customized to any desired configuration. Timber shuttering is the normal option for vertical concrete works. It is also used in combination with the steel elements. The shutter part in contact with concrete is called "form lining," while the supporting timbers are identified as "bracing." The bracings are created from timber that is straight, robust, and capable of bearing the desired loads. The form lining is generally some type of plywood or hardboard. Formwork is a professional trade, especially for the vertical structures. Bracing that is exceptionally intricate is designed by structural engineers.

Cement Basic - Structural engineering

2010-04-17T04:12:00.000-07:00

Concrete and cement are not the same thing. Learn the difference between the two and learn all about the different types of cement that are available for construction projects.

How many times have you heard someone say walk on the cement sidewalk? How about the concrete sidewalk? Which is correct? Actually, the correct phrase is "concrete sidewalk.” Many people use the terms interchangeably, but actually they are different.

Concrete is a mixture of cement, water, sand, and gravel. By volume, 10 to 15% of concrete is cement. As concrete hardens, the mixture becomes stronger. The hardening process can take years. Concrete has the ability to withstand the pressure of heavy loads because it has high compression strength. It can also be molded into any shape, can be made porous or watertight, and is a relatively cheap material for use in construction projects.

Cement is powder and is one of the main ingredients in concrete. Cement and concrete have been used in construction since at least the Roman Empire. Modern cement is made of limestone, silicon, calcium, and often aluminum and iron.

The type of cement used in almost all concrete is Portland cement. Portland cement has been around since 1824. The name Portland does not refer to a brand name, as many might think. The original inventor, Joseph Aspdin, was a British bricklayer and named his new invention “Portland” because its color reminded him of the color of the natural limestone on the Isle of Portland which is a peninsula in the English Channel.

Although Portland cement is the main cement used in concrete, there are other types of cement. The three types that are often mentioned are Portland, blended, and hydraulic. All Portland and blended cements are actually hydraulic cement. What is hydraulic cement, though? Hydraulic cement is actually the generic term in the construction industry. It refers to any cement that will set and harden after it is combined with water. Most modern construction cements are hydraulic. There are six different types of hydraulic cement:

* Type GU: General Use
* Type HE: High Early Strength
* Type MS: Moderate Sulfate Resistance
* Type HS: High Sulfate Resistance
* Type MH: Moderate Heat of Hydration
* Type LH: Low Heat of Hydration

Portland cement is a particular type of hydraulic cement. Portland cement contains hydraulic calcium silicates. There are eight specific types of Portland cement that fall into categories ranging from Type I to Type V. Type I and Type IA are general purpose cements. Type II and Type IIA contain tricalcium aluminate, but no more than 8%. To compare to the hydraulic cement types, some of the Type II cements meeting the standard for the moderate heat of hydration type.

Type III and Type IIIA are similar to Type I cements. However, they have higher early strengths because they are ground finer. Type IV cements are used in special types of structures that require a small amount of heat to be generated from hydration. Type IV cements develop their strength over a longer period of time when compared to other types. Finally, Type V cement has a high sulfate resistance which means it contains no more than 5% tricalcium aluminate.

The third type of cement is blended cement. Blended cement is also hydraulic cement and is made by mixing two or more materials. Usually the primary materials used in blended cement are Portland cement and slag cement. Fly ash, slica fume, calcined clay, pozzolan, and hydrated lime are also used. There are two main types of blended cement:

* Type IS (X): Portland blast furnace slag cement
* Type IP (X): Portrland-pozzolan cement

The X represents the amount of the second material that is in the mixture.

The reason that there are different types of cements is not only required because of the different uses of the cement, but also because of the type of materials available differ by location. Many of the types described above actually cross-over between the different categories. This allows for flexibility in particular construction projects. For example, different pozzolans and slag are available in different regions. As long as the desired properties of the concrete can be achieved usually, there is flexibility in the final choice of cement that is used.

Read more: http://www.brighthub.com/engineering/civil/articles/42795.aspx#ixzz0lM5zjmp3

Collapse Modelling of Soft-Storey Buildings

2010-04-02T20:06:00.000-07:00

Studies undertaken by the authors in recent years have indicated that the existing building stock at most risk of damage and collapse from earthquake excitation in lower seismicity regions such as Australia are unreinforced masonry buildings and soft-storey structures. Soft-storey buildings possess storeys that are significantly weaker or more flexible than adjacent storeys, and where deformations and damage tend to be concentrated. Soft-storeys commonly occur at the ground floor, where the functional requirements dictate a higher ceiling level or a more open configuration, such as for car parking or retail space, resulting in an inherently weaker and more fl exible level, as shown in figure 1. In high seismic regions, soft-storey structures and unreinforced masonry are banned, yet in regions of lower seismicity such building types and configurations are common, and are often occupied by organisations with a post-disaster function or house a significant number of people. This paper will address the performance of soft-storey buildings under earthquake excitations specifically. Research findings presented in this paper are directly relevant to low-moderate seismic regions worldwide such as Thailand, Vietnam, Hong Kong, China and Singapore, where similar soft-storey structures of limited ductility are commonly constructed.

Soft-storey buildings are considered to be particularly vulnerable because the rigid block at the upper levels has limited energy absorption and displacement capacity, thus leaving the columns in the soft-storey to defl ect and absorb the seismic energy. Collapse of the building is imminent when the energy absorption capacity or displacement capacity of the soft-storey columns is exceeded by the energy demand or the displacement demand. This concept is best illustrated using the Capacity Spectrum Method shown in figure 2, where the seismic demand is represented in the form of an acceleration-displacement response spectrum (ADRS diagram) and the structural capacity is estimated from a non-linear push-over analysis expressed in an ADR (as illustrated in Wilson & Lam, 2006).

The structure is considered to survive the design earthquake if the capacity curve intersects the demand curve, and collapse if the curves do not intersect. In regions of high seismicity, the maximum displacement demand could exceed 200-300 mm, which translates to a drift in the order of 5-10% in a soft-storey structure. Such drift demands are significantly greater than the drift capacity of soft-storey structures even if the columns have been detailed for ductility. This is the reason soft-storey structures have behaved poorly and collapsed in larger earthquake events around the world. In high seismic regions, buildings are configured and detailed so that in an extreme event a rational yielding mechanism develops to dissipate the energy throughout the structure and increase the displacement capacity of the building. Ductile detailing in reinforced concrete columns includes closely-spaced closed stirrups to confine the concrete, prevent longitudinal steel buckling and to increase the shear capacity of columns (Mander, 1988; Park, 1997; Paulay & Priestley, 1991; Watson et al, 1994; Priestley & Park, 1987; Bae et al, 2005, Priestley, 1994; Bayrak & Sheikh, 2001; Berry & Eberhard, 2005; Pujol et al, 2000; Saatcioglu & Ozcebe, 1992). The emphasis is on the prevention of brittle failure modes and the encouragement of ductile mechanisms through the formation of plastic hinges that can rotate without strength degradation to create the rational yielding mechanism.

Current detailing practice in the regions of lower seismicity typically allow widely spaced stirrups (typical stirrup spacing in the order of the minimum column dimension) resulting in concrete that is not effectively confined to prevent crushing and spalling, longitudinal steel that is not prevented from buckling, and columns that are weaker in shear. Design guidelines that have been developed in regions of high seismicity (ATC40, FEMA273) recommend a very low drift capacity for columns that have such a low level of detailing. The application of such standards in the context of low-moderate seismicity regions results in most soft-storey structures being deemed to fail when subject to the earthquake event consistent with a return period in the order of 500-1500 years.