Longitudinal Post-Tensioning in Precast Concrete Deck Panels

[whatname]

I'm working on the design of a three-span bridge using full-depth precast concrete deck panels on steel beams.

I plan on using longitudinal post-tensioning in the deck panels to to resist the effects of negative moment at the piers.

I believe that I have properly designed the strands under service load conditions to ensure compression in the slab, but I'm somewhat uncertain about how to check for ultimate capacity.

Performing a conventional composite beam design at this location, where only the reinforcing steel (prestressing strands) act in conjunction with the beam would result in an inordinate number of strands.

One thought I have is that because I've designed the strands to ensure that the slab will always be in compression (under service loads), is that the slab is now available to me to transform into an equivalent steel section for composite design, and that I could perform the check as a typical composite beam.

Does anyone have experience with this type of design, or any thoughts on the matter?

 

[MichSt]

I think a conventional negative moment design over the pier under factored loads at ultimate capacity would be warranted. It sounds like you need to increase your girder section over the pier to get your design to work out.