Rectangular Connection Element: Interaction Equation Valid for Compressive Loads?

[GearsNsparks]

Looking at the interaction equation for rectangular connecting elements in AISC 360 - Equation 9-1:

Mr/Mc + (Pr/Pc)^2 + (Vr/Vc)^4 <= 1.0

Is this equation valid for axial compression loads Pr/Pc)?

 

[Hokie93]

Are you asking if Equation (9-1) from the Manual can be used when only axial load is applied to a connection element? That is, shear and moment are zero and axial load is non-zero? If so, I would say the answer is "no". For that case, the axial strength should be determined per AISC 360-10 or AISC 360-16 Section J4.4.

 

[GearsNsparks]

I was wondering if I had combined in-plane shear, in-plane bending, and compression axial loads on my connecting element, if this equation was still valid or if it was only valid for in plan shear + bending + tensile axial loads.

Additionally, does that extend to Doswell's general equation (67 from Plastic Strength of Connecting Elements) for in and out of plane bending, shear, axial loads, and torsion.

 

[Hokie93]

I believe Eq. (9-1) is valid for tensile and compressive axial loads. Since the interaction equation is based on a plastic strength approach, it assumes the element in question is stocky, or well-braced or stiffened, to the extent that the plastic strength of the element can be fully mobilized. Stability of the element would need to checked separately. If you determine the element will buckle elastically (prior to yielding), you should probably consider using a different interaction equation for load combinations involving axial compression.