Horizontal Bracing Connection Design for Structure Assigned to SDC "D"

[Kussro]

I'm designing a braced steel structure assigned to Seismic Design Category "D". The structure utilizes special concentrically braced frames (SCBF) for the vertical elements of the seismic force resisting system. Lateral seismic loads are delivered to the SCBF's by horizontal bracing members, not deck diaphragms. Does the horizontal bracing and bracing end connections need to be designed per the provisions of AISC 341 or do these provisions apply only to the vertical bracing elements in the SCBF's?

 

[JoshPlumSE]

The AISC seismic design manual has a chapter 5 (in the manual, not the spec) which covers portions of the Seismif load resisting system that are not part of frames. I believe this would apply to your horizontal braces. The AISC manual mainly talks about diaphragms and collectors. But, I think you can extend the concept out to include your braces.

Essentially, the manual just shows that the horizontal diaphragm design forces must be calculated using the Fpx equations from ASCE-7.

When I was just starting out, a senior engineer told be to design my horizontal bracing system as if it were a rigid diaphragm (using accidental eccentries and such) because there was enough bracing in the system that the overall structural behavior would be pretty close to a rigid diaphragm. That made sense to me.