masonry bearing and shear capacity
 

masonry bearing and shear capacity
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
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.