huangyhg

laterally braced beam
i have to design a lintel 40 feet long. it will be supporting 12" solid cmu wall above so top flanges will be embed. is it laterally supported or not. i think not.
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it will be laterally unsupported unless you can provide braces to it from the nearest floor or roof.
it depends. does the 12" cmu go up to a diaphragm, but there's no other diaphragm lower on the wall?
for example, if there's a lower diaphragm, the wall might be stiff enough out of plane to provide bracing.
i do not consider a steel lintel in a masonry wall braced. you could go about determining if the top flange is braced if it is embedded into a bond beam above and the bond course is attached to vertical reinforcing at the ends of the opening to transfer the load up and down to the floor/roof diaphragms. being as this is 40' long i would not count on that, or be very careful about using that.
the bottom line is that it's assumed unbraced unless you can figure out a way to show that it's braced.
the 13th ed. spec. appendix 6 provides ways to determine if a beam is braced against twist or compression flange lateral translation--prove one or the other or both.
depending on the details of your situation, you might be able to show that it's braced. of course it requires plenty of judgment.

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