huangyhg

lifting beam design
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?
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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.
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?
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?
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.

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