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Fw: original issue - seismic loads on p t conc parking structures

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I know that Dr. Nigel Priestley at UCSD was doing some cyclic testing of
P/T beams for seismic consideratoins last summer.  You might wish to find
out if the results of those tests have been published.

T. Eric Gillham PE

> From: Baldridge & Associates Structural Engineering, Inc.
> To: seaint(--nospam--at)
> Subject: Re: original issue - seismic loads on p t conc parking
> Date: Friday, July 31, 1998 5:52 PM
> 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
> 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
>  1921.8.4.1 - 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.