Masonry bearing and shear capacity

[HeavyCivil]

I have never been fully confident that I am using the shear capacity equation of a CMU wall correctly-
ACI 530 3-18

Vn= Vm+Vs where

Vm = [4 - 1.75(Mu/Vudv)]An SQRT(fm')+.25Pu. I dont count the face shells of blocks towards An, but have seen this done in sample calcs - am I being too conservative?

and

Vs= .5*(Av/s)fvdv

Do we count reinforcing boardering openings (windows and doors) towards Av or just consider our nominal bar (say #5s at 48" oc)?? For dv, again, do we consider face shells as contributing?


On another note, I am unable to find a code minimum for beam bearing on CMU walls, although I'm sure it is referenced somewhere. I am responsible for designing a retrofitted hoist beam embedded in 4" CMU walls at each end but cannot penetrate exterior face shells so I need to determine how rugged of a steel support I will anchor to these walls to accomodate the beam.

Thanks,
VTEIT

 

[Lion06]

If the face shells are mortared, then yes, count on them.

I'm home again today, so I don't have any references in front of me, but masonry bearing is typically limited to 0.25f'm.

As for bars around openings, I'm assuming you mean the horizontal bars above/below openings. I wouldn't count on them as part of your Vs.