Material Allowable Stress Limit 1

[BuoyancyBloke]

First time poster

Sorry if this seems a really simple question but....

I am doing some steel design and have used a maximum stress limit of 0.67*yield strength as my limit tensile and 0.4*yield as my shear limit. My client has come back asking where i get 0.67 and 0.4 from and has suggested 0.6 from AISC code. I do not have this AISC code and would like to continue with my 0.67 and 0.4 factors.

My question is can anyone tell me which standard these factors come from i.e ANSI or ASME standard or other. I cannot for the life of me recall as i have used them forever never referencing them and never had anyone query it as it always seemed a universal set of factors.

Much obliged for your assistance

 

[JStephen]

One place where you have these factors is in AISC-ASD. Compact wide-flange beams with lateral supports use .66 times the yield stress (which in former editions was rounded to 24,000 PSI for A36 steel, or 2/3 the yield stress; currently shown as rounding to 23,800 PSI). Non-compact sections use the 0.6 factor. The 0.4Fy factor is also from AISC-ASD.

If you're actually designing anything that falls under the AISC code, I highly recommend that you have a copy. It is important to know the limitations on where those stresses are used, as well as the stress values themselves. The members in question have to fall within certain width/thickness/height ratios, have lateral supports at certain intervals, etc.

These are understood to be for static loading of ductile members, and do not include fatique effects.

 

[DowneastTech]

Allowable tensile stress of 2/3 of yield is used in several API specs, for instance API-6A,API-16Q, and several others. I believe American Bureau of Shipping also uses this allowable. We have used this allowable for years all over the oilfield. The 40% of yield for principal shear is AISC and ASME Boiler and Pressure Vessel Code (not to be confused with maximum combined shear stress also called stress intensity).


DowneastTech
Mechanical Engineer
Magnus R & D, Cypress, TX