bracing system design

[johndeng]

for wind/sesmic "x" bracing systems design, best people here always suggest using tension only (let the compression member buckle), but all references I have are based on compression member capacity. I feel if member buckled repeatly at compression, it will lose some capacity when it take tension. Also if we can let compression member buckle, we should let them buckle in plane, not out of plane. How do we control this?

Thanks

 

[frv]

Tension-only bracing has been used forever. Nothing wrong with it.

I believe you are not allowed to use it in certain seismic categories.

The L-r distances involved in typical X-Braces used for tension-only would usually result in elastic buckling. Why would you care whether it buckles in or out of plane?

 

[johndeng]

Thanks frv for your quick response.
I just think out of plane buckle may damage wall surface if all framings are covered. So for HSS6X4 I may control it to buckle in plane, but not for HSS6x6

 

[JAE]

For something to buckle that much to damage wall surfaces, there would be far more damage to the building that would concern me more.

You're talking about a major seismic event to cause a large scale buckling of that magnitude. The wall would be damaged by the lateral frame deflections anyway.

Usually you try to get the braces to buckle outward - see AISC's commentary on gusset plate designs.