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Home > Forums > Mechanical Engineers > Activities > Mechanical engineering other topics Forum

Different approach

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Bert2 (Mechanical) (OP)

19 Mar 12 11:58

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.

Cockroach (Mechanical)

20 Mar 12 9:05

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

GregLocock (Automotive)

20 Mar 12 23:11

Simple answer, yes obviously, build an equivalent beam. Ignoring compression in the concrete makes it rather futile though.

Cheers

Greg Locock

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