Combined loading on HSS, bolts, plates, solid bars and welds

[SuG89]

Hello,

I am using the 13the Edition of AISC Manual and my question is about combined loading. For round and rectangular HSS, the combination equation is given in AISC Specification Section H3.2.

[Pr/Pc + Mr/Mc]+[Vr/Vc + Tr/Tc]^2 <= 1.0

For bolts, the combination equation is given in AISC Specification Section J3.7. This equation is an approximation of the elliptical curve as per the following equation.

[Pr/Pc]^2 + [Vr/Vc]^2 <= 1.0

What is the reason for squaring the axial forces in the bolt combination equation and not squaring for the round/rectangular HSS combination equation?
Also, which combination equation should be used for combined loading on plates, solid bars and welds?

Regards,
Su

 

[SuG89]

Hi again, can anyone shed some light on this topic?

 

[JoshPlumSE]

Take a look at the commentary for J3.7. The test data very much supports this elliptical failure curve. The research papers that derive this should be referenced (I would hope) in the commentary.

For members subject to combined stress, the interaction is likely a lot more complex. Axial stresses interact with flexural stresses which warrant a little extra conservatism in this equation. There is some discussion in the commentary as well. But, it is not as robust as I would like. I used to have a copy of the SSRC guide to stability. I imagine they discuss this in a bit more detail. But, I don't have access to it anymore to verify what it says.

 

[SuG89]

Thank you for sharing this information!