Lifting Beam Design

[pat2]

I am load rating 2 previously constructed lifting beams. I have found that ASME B30.20 requires a 3.0 safety factor against yielding. Does OSHA require a more stringent safety factor? I have found on the internet that Ontanio OSHA requires a 5.0 safety factor against failure.

Furthermore, what is your opinion of how the satefy factors should be implenmented?

To give a couple of easy examples of how I interpret the proper implentation of the Safety Factors is:

Bending: Fb=.6Fy/3.0 and

Shear rupture: Fv=.3Fu/5.0

Does anyone see this a different way?

 

[jjeng2]

Im not familar with this standard but I think what you are doing is going overboard. Fy/3.0 is a 3.0 factor of safety against yielding. Fy is the yield stress. .6Fy is the ASD allowable stress. Similar for shear rupture. I dont think you need to apply both factors.

 

[pat2]

I have concluded that you are correct.

I instead multiplied my live loads by 1.8. Since ASD uses an approximate 1.67 factor for yield, 1.8*1.67=3.0. This satisfies the 3.0 safety factor requirement.

Anyone have comments on this approach?

 

[jjeng2]

Im a bit confused by your last post. Does the ASME standard use allowable loads or ultimate loads? If they use allowable loads, i.e. being compatible with ASD:
Assume 36 ksi steel:
Fy=36
Your allowable stress=36ksi/3=12ksi
Fu=58
Your allowable shear rupture=58ksi/5=11.6ksi

Now if the ASME standard uses ultimate loads..
Apply LRFD load factors to your live and dead loads to get a total load. Use the ultimate strength of the steel, so for 36ksi steel use 58 ksi.
Your allowable yield stress now equals: 58/3=19.33 but your loads are factored.

Does this make sense?

 

[JStephen]

Do you have mill test reports on your steel?

Practically all of our structural work is "A36". But I understand that much of the material we use is actually dual-certified, with a higher yield strength (maybe 50 KSI, not sure). Anyway, worth checking on.

I'm not sure what you're actually making -it sounds like what I hear called a spreader bar- if so, AISC-ASD may be governed by buckling due to lack of lateral support, or column buckling, rather than by yielding.