Maybe I'm missing something, but I think you have discovered another issue
on which the building code is silent.
If this were a shear friction problem, you could take the vector sum of the
shears to find Vu and the capacity phi*Vn would just be based on the total
steel area without respect to direction. it gets a little fuzzier when you
are including Vc as well as Vs in the capacity calculation.
I think I would be inclined to use a linear type unity equation to make sure
that the sum of the fractional capacity consumed in each direction adds up
to less than 1.0. Say (Vu/phi*Vn)in-plane + (Vu/phi*Vn)out-of-plane <= 1.0.
I couldn't find anything in ACI 318 or UBC 97 that specifically tells you
how to handle this situation, which is curious, since it surely happens in
columns in moment frames subject to bi-axial loading, as in earthquake and
The Commentary to ACI 318, section R10.3.6 makes reference to the ACI Design
Handbook and the CRSI Handbook for biaxial bending design, but I don't know
if these discuss anything more than the biaxial bending problem.
From: Mark Miller [mailto:milm(--nospam--at)exchange.chemeketa.edu]
Sent: Friday, March 02, 2001 3:19 PM
Subject: Foundation wall shear.
I am looking at designing a foundation / basement wall that will be
loaded with shear in both the in plane direction (using it as a
shear wall) and in the out of plane direction (from the soil pressure).
I can calculate the shear load / stress in both directions, but how do I
resolve these because they could act simultaneously?
Am I thinking of this right, or am I making this too hard?
Mark Miller, P.E.