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Re: AISC "Seismic Provisions for Structural Steel Buildings", Section 13.3.a

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A flexible brace in a system of rigid braces connected by rigid diaphragms may not "draw" much load.  Also, a brace with a small footing may not be capable of receiving much load prior to loss of stiffnes at the foundation level due to footing rotation and loss of ground contact.  The term "the system" is very comprehensive.  If your drag struts can only carry so much force to the brace, that's all it will ever recieve.  In a redundant system, relatively weak, but ductile drag struts may be justified, and may limit the load felt by a particular brace.

Tom


Thomas B. Higgins, P.E., S.E.

Group Mackenzie
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>>> "Sherief S. Sakla" <sakla2000(--nospam--at)softhome.net> 11/19 5:10 PM >>>
I need clarification regarding AISC "Seismic Provisions for Structural Steel
Buildings", Section 13.3.a.  It states that :
"The required strength of bracing connections shall be the lesser of the
following:
(a.) The nominal axial tensile strength of the bracing member, determined as
RyFyAg

(b.) The maximum force, indicated by analysis, that can be transferred to
the brace by the system."

Is not the force calculated from part (b) always greater than that
calculated from part (a)!!!

Regards,

S. Sakla, P.E.





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