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masonry bracing top flange of steel
does anybody know if masonry braces the top flange of steel to prevent ltb. are there any special details that have to be made for this to be done? i have the cmu sitting on the top flange of the steel section and i'm trying to limit the size.
thanks
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i've known engineers who have said yes and others who have said no. the articles i've read indicate that masonry should not be assumed to provided bracing against ltb. all the engineers who i know who design lintels assume that the masonry provideds bracing against ltb.
this is tricky. some say yes, some say no, i say "depends"
if the course sitting directly on the beam is a bond beam, and that bond beam can support 2% (rule of thumb, comes from salmon and johnson, design of steel structures), of the compressive load in the beam's flange, in addition to its other lateral loading (wind/seismic), then yes, it is laterally supporting the beam.
for simplicity, the compressive load in the flange is the maximum moment (in kip-inches) in the beam (m) divided by the depth of the beam (d) minus the thickness of the beam's flange (tf).
f = m/(d-tf)
if you're supporting masonry, you have to limit your deflection to l/600
i would not count on masonry for bracing. however, if you are near a roof or floor, you could provide bracing to the lintel from that level as long as it does not affect the architecture.
masonry at right angles to the axis of the beam provides a brace point where crossing the beam.
you might do a google search on this site. there was a long discussion of this issue some time ago. don't count on getting a straight answer.
we do not assume the top flange is laterally braced by a cmu wall on top.

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