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Subject: RE: BRACED FRAMES

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Rick Drake offered the following:

>Hollow Structural Sections (HSS) have performed very poorly in low-cycle
fatigue
>tests.  Therefore they have more restrictive b/t ratios for seismic
>applications.  These restrictions were also in the 1994 UBC (Section 2211.7.3)
>and are not new.  Yes, you are still effectively precluded from using large HSS
>sections in high seismic zones.

>Rick Drake, SE
>Fluor Daniel, Aliso Viejo

Rick was right, however, the UBC allows some loop holes that complicate the
process further.

UBC Section 2213.8.5 says that noncomplying sections may still be used for one
and two story buildings, provided that (1) the design forces are increased by
omega-O, and (2) the design still meets AISC provisions.  The AISC provisions I
am thinking of are the "compactness" requirements, which may require some
elaborate calculations (Q-factors, etc.) in order to determine the compression
strength of the "unstiffened" section.

Martin