huangyhg

masonry deflection
does anyone know of a good source for suggested deflection limits for masonry? in particular i am looking at limits for a cantilevered wall.
i would check the masonry society website and building code requirements for masonry structures aci 530-99.
i have checked these and i see only recommendations for simple span situations. i have a cantilever and need some advice for that situation.
check site:
typically you can double the length of your cantilever and use that for your simple span length.
my wall is 12' tall, if double it and use the limit of 0.007h, the limit becomes about 2". does this seem reasonable? it seem large to me, but i am not very experienced with masonry.
it looks as if you are using the seismic "drift" limit for a deflection.
is the wall a structural wall?
does the wall serve an architectural purpose?
how much movement can the connections to this wall tolerate?
is there a drift limit? why?
is there a safety issue connected in any way with it?
how about human sensitivity to it's movement?
are you looking at deflections in plane or out of plane?
is this a masonry veneer, or is it a reinforced cmu block wall?
the movement limits for masonry walls are several. and there's alot of discretion in the art of predicting and controlling the behavior.
the wall is reinforced and is used to take some of the lateral loads from the bents of a metal building in one direction (shear wall), and is a seismic load on the bents in the other. it is an architectural wall, so cracking and out of plane movement are the concrens. in other words, how much should i allow the bents deflect under load so that the wall is not adversely affected? the metal building is approximately 25' tall and the cmu wall is about 12' tall and is 8" thick.
i would bet that the thrust from the bent for total max loads is the critical issue. you will likely need a heavily reinforced pier to resolve the forces. the foundation connection will be very critical to develop the reaction you need at the joint.
as far as deflection, probably the architectural finish won't control so long as you detail joints to accomodate rotations well.
likely more critical is the effect of deflection on the stresses in the steel bent.
it's probably best to model the frame on the computer as well as hand calcs to experiment with the system and understand the limits of restraints and deflections.
the understanding of preliminary study should show you how to get to a final design.
it depends on what you want the limit for! if it is for the assessment of an existing wall then the limit occurs when the wall resultant is on the limit of the middle third of the wall when wind or other lateral pressure is taken into account.
for a new wall.....? define your tolerence and get a good contractor .

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