Analysis and Design of the Fastener

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_v of 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_v of 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

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:

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

AISE SERVICE CLASS

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.

BASIC CRANE COMPONENTS

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

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?

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

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.

Avoiding Pitfalls In Crane Projects

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.

Collapse Modelling of Soft-Storey Buildings

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.