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# Different approach

## Different approach

(OP)
I have a question regarding cast in situ bridge girders relative to a load imposed considering pre-tensioning and ultimate elongation of strands.

Specific details;

Length of span = 30M
Grade of Strands = 270k / 0.6"
Pre tension imposed = 19500kg / Strand
Neglect compression effects of concrete girder.
Load = UDL of 270Te (270000Kg)
Neglect any Dynamic inputs – only consider as a static load.

I'am aware of AASHTO std however using Hooke's law principles is there a way to calculate Sigma / Epsilon / x elongation; given the pre-load applied..? guess it won't be as simple as to '-' the pre-load off the imposed load...

Thanks for any replies! – I know it's a bit different.

### RE: Different approach

I guess you could do a deflection based on load and obtain the equation of that curvature. Then the elongation would be the arc length of that geometry less the length of the undeflected member. This is the classical approach to beam design taught in static courses with a little bit of calculus.

Regards,
Cockroach

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