Bridge pre-tension question

[Bert2]

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.

 

[graybeach]

Seems like you mean you will be post-tensioning rather than pre tension.

You could calculate the final length of the cable based on the geometry of the cable path. If you know the stress you want it to have, you could calculate how much the cable would shorten if that stress were released. Before stressing, put a mark on the cable at that point, and jack until the mark is reached.