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Masonry Wall out of plane deflection limit

Masonry Wall out of plane deflection limit

Masonry Wall out of plane deflection limit

(OP)
When designing masonry buildings ACI 530 states an out of plane deflection limit of 0.007*h which must include p-delta affects. The IBC states out of plane deflection for walls should be L/240 for brittle finishes. We have used 0.007*h in the past, but we are wondering if we should really be using L/240. for a 20'-0" wall height, it is a pretty large difference in deflection. L/240 = 1" 0.007*h = 1.68". Which is the correct deflection limitation? 1.68" seems like a lot in 20'-0".

RE: Masonry Wall out of plane deflection limit

Brittle finishes mostly means plaster finish on whatever wall.

Your deflection is governed only by ACI 530 unless the CMU has a plaster finish.

1.68" is a lot, but that is probably based on a load that the structure will never see. You don't want to know how much I allow wood stud walls to deflect.

RE: Masonry Wall out of plane deflection limit

(OP)
AELLC,
If I used the L/240, would I still need to include p-delta affects?

RE: Masonry Wall out of plane deflection limit

yes, to be legal, but I am sure 99% of engineers don't, LOL

RE: Masonry Wall out of plane deflection limit

I actually would not, because I designed CMU for decades way before ACI 530 raised the extra complication of p-delta in CMU.

I had one minor actual failure in CMU and it had nothing to do with this issue here.

RE: Masonry Wall out of plane deflection limit

(OP)
Interestingly enough, if I used 0.007 with p-delta affects and compared it to L/240 without p-delta affects, the reinforcing comes out the same. With the 0.007 requirements, the bending moments in the wall are higher with the p-delta affects and govern the steel, with the stricter deflection requirements of the L/240, deflection controls the wall reinforcing. So for this particular project, it doesn't matter either way. Our firm has designed masonry buildings for a long time before me and ACI 530 and we have never had any problems either. Thanks for the input.

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