huangyhg

concrete frame with masonry block infill
hi,
i have a three storey structure with the primary load resisting system being a reinforced concrete frame. i do have masonry infill and herein lies the question.
at exterior wall locations, how do i detail the masonry wall connection to the r/c beams such that it can transfer wind loads to the upper and lower beams but does not transfer gravity loads to the frame below.
the architect is also concerned about the hairline crack that will develop between the wall and the beam.
any comments?
thanks

i'd limit the deflection of the concrete beam to l/600 and tell the architect to design a window or something.
has he seen cracks in masonry due to deflection of concrete beams?
use head restraint ties.
tomfh,
can you little more elaborate on head restraint ties? are there any commercial brands? can they be fabricated on site?
clefcon
they are generally proprietary products. there are a number of brands.
here is one example:
these connectors will form a working joint on the exterior face of the building. this may create a waterproofing problem and will crack finishes.
in most concrete buildings the majority of gravity loads are the self weight of the structure itself therefore the majority of the deflection occurs before the infill walls are placed. i have always made a hard connection to the beam above and require that the connection not be placed until all shoring/reshoring has been removed. this will allow for load transfer thru the walls in accordance with stiffness. this detail has been used in south florida for years and i am not aware of there ever being a problem.
the conection can consist of threaded dowels into form savers, embed plates in the concrete beam with a plate welded after forms are removed, dovetail anchors, epoxy dowels, etc.
we do lots of condos with p/t slabs. same question with infill exterior masonry walls. pvc sleeves are placed thru slabs to allow for vertical reinforcement to continue thru the slabs. as far as i know everyone uses this detail without problems and in this instance the edge of a slab isn't nearly as stiff as an edge concrete beam.
fortunately concrete is a very forgiving material and it will redistribute loads whenever possible if it is overstressed.
thanks ron,
i do, and i'm sure the architect will share the concern about the waterproofing and cracking issues with the use of the wall restraints.
ataman

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