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Re: original issue - seismic loads on p t conc parking structures[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Re: original issue - seismic loads on p t conc parking structures
- From: "Baldridge & Associates Structural Engineering, Inc." <base.engr(--nospam--at)internetMCI.com>
- Date: Thu, 30 Jul 1998 21:52:33 -1000
The original inquiry "seismic loads on post tensioned conc parking structures" related to UBC seismic detailing requirements that make sense for conventionally reinforced frames, but seem to get lost in translation when applied to long span (60') post tensioned beams typical in parking structures. For example in seismic zone 2 if you used a frame to resist forces induced by earthquake forces the beams would have to be proportioned 1918.104.22.168 - the positive mom strength at the face of the joint shall not be less than one third the neg moment strength at the face of the joint. In a post-tensioned beam (due to the post tensioned tendons at the top of the beam) this might actually require that there would have to be more bonded reinforcement in the bottom of the beam then in the top to achieve only one third the neg moment strength (which is provided by a combination of both bonded reinforcement and pt tendons). The intention is to develop and maintain the strength and ductility of the member through a number of cycles of reversed inelastic. These provisions are based in part on experimental and analytical studies of Reinforced Concrete (probably not post-tensioned concrete) members under earthquake simulated loading. - With the application of a compressive force due to post-tensioning some of these provisions may either be to conservative or not conservative enough. These concerns were reinforced after discussing this issue with the PCA and Bijan Aalami (ADAPT) Any comments or good sources of information on seismic testing/performance of post-tensioned concret frames would be appreciated.
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