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Re: 70%-30% Bracing Load Distribution

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That may be the code, but it doesn't make logical sense.  If I have a cyclic load, and my "compression" strut buckles, leaving only the tension strut, then when the load reverses, my (former) tension strut will buckle and my (now failed) compression strut will be expected to take the full tension load. Since these failure loads are occurring entirely in the plastic range, the buckling may be significant instead of incidental, as would be the case if plastic deformation wasn't anticipated. In other words, a slightly buckled member will probably perform under tension, but a severely buckled one probably won't, though it will provide a great deal more structural damping (hysteresis) than a purely linear response system.

Take that with a grain of salt, as the only rocking and rolling we do around my area involves hurricanes.

Scott, William N. wrote:
Rainer,
 
No. The bracing is for cyclic loading (seismic) and the bracing will buckle under compressive loading before the tensile loading is fully mobilized. That means the tension brace needs to be designed for the full load. See AISC Seismic Provisions.
 
Bill

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