Masonry Wall out of plane deflection limit

[jeffhed]

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".

 

[AELLC]

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.

 

[jeffhed]

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

 

[AELLC]

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

 

[AELLC]

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.

 

[jeffhed]

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.