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.

FEM SERVICE CLASS

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

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

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

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

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.