Stress Analysis of Lifting Plate With Bail

  • Thread starter Thread starter Drew Sandlin
  • Start date Start date
  • Tags Tags
    Stress analysis
AI Thread Summary
The discussion focuses on the stress analysis of a custom lifting plate designed for overhead cranes, addressing concerns about contact stresses, bending strength, and the impact of manufacturing methods on fatigue life. It emphasizes that local contact stresses are less critical than gross section stresses due to the ductility of the low-strength steel typically used, such as A36. The analysis should include checks for shear and tensile failure, while assuming that stresses in hypothetical beams can represent actual plate stresses. The ASME BTH-1 standard provides safety factors but leaves stress determination to the analyst, and both laser cutting and waterjet cutting are deemed comparable for low cycle applications. Overall, the approach should ensure compliance with safety standards while considering the specific loading scenarios.
Drew Sandlin
Messages
5
Reaction score
0
TL;DR Summary
How do you analyze the stresses on the bail on a lifting plate?
I'm designing a custom lifting plate that has two shackles hanging from it and a large slot at the top for hooking into an overhead crane. I have a few stress analysis questions:

1. The plate will be cut on a waterjet table, which means the slot will have sharp edges, and that the hook will contact the inside of the slot on the lifting plate at two points. See the attached pictures. What is the best way to analyze these contact stresses? Case 4 in Table 14.1 in Roark's Formulas for Stress and Strain, page 704? Is this something I should even be concerned about?

2. The bail at the top of the lift plate is approximately a curved beam. Can I analyze an equivalent curved beam that fits within the plate profile, and assume the stresses in the actual plate will be no higher than the stresses in this hypothetical curved beam?

3. For the bending strength of the plate, can I take a similar approach to (2) and analyze a smaller rectangular beam that fits within the plate profile and assume the stresses in the actual plate will be no higher the stresses in this hypothetical beam?

4. I've been reading through ASME BTH-1 and my understanding is it gives safety factors for certain loading scenarios and member designs, but leaves the method of determining stresses up to the analyst. Is that an accurate statement?

5. Does laser cutting this plate versus waterjetting it affect fatigue life for the plate? I couldn't find anything in ASME BTH-1 that discusses this. I could have missed it. Are there any considerations that need to be accounted for in the heat affected zone if components in a lifting device were laser cut?

Maybe what I'm really asking for is, "how would you approach analyzing this lifting plate to show it's compliant with ASME BTH-1?"
Hook Plate Cross Section.png
Lift Plate.png
 
Last edited by a moderator:
Engineering news on Phys.org
Trying to remember from when I wrote the corporate procedure for lifting calculations from over ten years ago...

Drew Sandlin said:
I've been reading through ASME BTH-1 and my understanding is it gives safety factors for certain loading scenarios and member designs, but leaves the method of determining stresses up to the analyst. Is that an accurate statement?
Yes

Lifting beams and fittings are normally made from a relatively low strength steel, such as A36. Such steel is ductile. Lifting calculations are made using gross section stresses, not local contact stresses. This was specifically stated in one code, which stated that the code calculations applied to gross section stresses, not local peak stresses from FEA. Because the steel is ductile, local yielding removes stress concentrations from sharp corners. The crane hook will round off the contact surfaces. Also, between the ductility and the low carbon content, there should be no difference between laser cut and waterjet cut plates. This statement is specific to relatively low cycle applications. If the lifting plate will see millions of load cycles, you will need to design for high cycle fatigue. I think that high cycle fatigue is mentioned in BTH-1. If not, look in the structural steel codes.

The steel plate is analyzed in steps. The first step is checking for shear failure as shown in the diagram below. The diagram is from Aircraft Structures, by Peery.

Shear.jpg
The next step is checking for tensile failure as shown in the diagram below from the same book:

Tensile.jpg


Riveted thin plates used in aircraft have other failure modes that need to be checked. Those modes do not apply to your situation.

Drew Sandlin said:
The bail at the top of the lift plate is approximately a curved beam. Can I analyze an equivalent curved beam that fits within the plate profile, and assume the stresses in the actual plate will be no higher than the stresses in this hypothetical curved beam?
Such a short beam has fixed ends, so shear must also be calculated. Do not be surprised if the shear and tensile calculations shown above are sufficient to show safety.

Drew Sandlin said:
For the bending strength of the plate, can I take a similar approach to (2) and analyze a smaller rectangular beam that fits within the plate profile and assume the stresses in the actual plate will be no higher the stresses in this hypothetical beam?

Sure, that works. After the areas around the three points of applied force are strong enough, the rest of the plate is normally good. Unless, of course, you are trying to minimize the overall height of the plate.
 
  • Informative
  • Like
Likes berkeman and Lnewqban
Posted June 2024 - 15 years after starting this class. I have learned a whole lot. To get to the short course on making your stock car, late model, hobby stock E-mod handle, look at the index below. Read all posts on Roll Center, Jacking effect and Why does car drive straight to the wall when I gas it? Also read You really have two race cars. This will cover 90% of problems you have. Simply put, the car pushes going in and is loose coming out. You do not have enuff downforce on the right...
I'm trying to decide what size and type of galvanized steel I need for 2 cantilever extensions. The cantilever is 5 ft. The space between the two cantilever arms is a 17 ft Gap the center 7 ft of the 17 ft Gap we'll need to Bear approximately 17,000 lb spread evenly from the front of the cantilever to the back of the cantilever over 5 ft. I will put support beams across these cantilever arms to support the load evenly
Thread 'What's the most likely cause for this carbon seal crack?'
We have a molded carbon graphite seal that is used in an inline axial piston, variable displacement hydraulic pump. One of our customers reported that, when using the “A” parts in the past, they only needed to replace them due to normal wear. However, after switching to our parts, the replacement cycle seems to be much shorter due to “broken” or “cracked” failures. This issue was identified after hydraulic fluid leakage was observed. According to their records, the same problem has occurred...

Similar threads

Replies
14
Views
27K
Replies
22
Views
5K
Replies
1
Views
10K
Back
Top