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

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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

 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.