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footing pedestal design in seismic zones 2,3 &4
per ubc 1922.10.3, structural plain concrete members are not permitted in seismic zones 2, 3 & 4.
ubc 1921.4.1 refers to "frame members". is this refering to moment frame members only or does it include members of a braced frame structure?
chapter 21 of aci seems to only refer to moment frames.
i am designing a footing pedestal for a steel column of a braced frame structure and i want to be sure i follow the correct design procedure. do i have to use a minimum reinforcement ratio of 0.01? (per ubc 1921.4.3 and aci 21.4.3.1)
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i would suggest using at least the minimum reinforcing ratio since even if you have some sort of bracing in the framed structure that reduces or even eliminates bending moments in the bases of the steel columns, due to free elastic length of the pedestrals some bending moments will appear there.
in some structures we have designed in europe that are consisting of a braced steel frame resting on pedestrals
(2 - 3 feet) and combined footings we designed the pedestrals as concrete columns altough codes suggested using minimum reinforcement or no reinforcement at all. the result (after capacity design) was that the reinforcement required as well as the confining reinforcement greatly exceeded the minimum values.
if the analysis shows that there are negligible moments is the bases of the pedestrals, minimum reinforcement is probably ok otherwise i would suggest treating them as rc columns...

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