Pre-stressed precast bridge beam modelling - Deflection issues arising from pre-stressing

[Cian_Lynch]

Hi

I'm modelling a precast, pre-stressed bridge which consists of symmetric internal Y beams and asymmetric edge beams. My edge beams experience a horizontal deflection (as well as the expected vertical deflection) due to the pre-stressing loads. This is due to the eccentricity of my tendon layout so the resolution would be to re-arrange my tendons to account for this. Has anyone else encountered this issue? Just wondering if there is a more time efficient solution than adjusting the layout, running the model, re-adjust the layout and so on. Would I be better doing a manual calc on the forces & eccentricities, balance them and then model the resulting layout?

Regards
Cian

 

[TehMightyEngineer]

If it were me I'd keep brute forcing it (adjust, model, re-adjust). It's less prone to errors, simpler to implement, and faster in the short run. If you're going to be designing these beam multiple times (like if you work for a precaster and they're going to be used for multiple jobs) that's when I'd look at creating something to solve for the appropriate strand layout.

Also, I assume that the precaster only has so many predefined strand locations in their stressing bed so the number of available combinations can't be that large.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[IDS]

I'd suggest the opposite. It's a simple calculation to check that the centroid of the strands lies on the vertical centroidal axis, so do that to start, then adjust if necessary.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[Cian_Lynch]

Thanks for the input. I'll run both methods on this one to confirm everything's doing what it should be doing.