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Muti span bridge design moments

Muti span bridge design moments

Muti span bridge design moments

What guidance is available on the calculation of bending & shear moment calculation methods for a multi span reinforced concrete bridge?  Thanks in advance.

RE: Muti span bridge design moments

Guidance?  You will have to use a general analysis structural software program as you will need to include the integral, monolithic columns in the analysis.  Its a real pain to do my moment distribution especially when doing the live loads.  Of course there are design aides for placing the live loads to effect the maximum responses (reactions, shears and moments) so that may not be as bad as it seems - I haven't done it for a long time, though I can say "been there done that!".

If I've mistakenly assumed that the structure is monolithic and it is really just a concrete superstructure resting on bearings atop the columns or bent then your problem is even simpler as you can find the appropriate responses with design aides such as AISC's Moments, Shears, and Reactions booklet.

RE: Muti span bridge design moments

You will have to specify whether each span is simply supported or continuous beam. As Qshake says, any discontinuity in any direction is important and that includes bearings, expansion joints or end conditions.

RE: Muti span bridge design moments

To design a multiple span continuous bridge you will need shear and moment envelope. (i.e. maximum and minimum for each section, say 10 per span)
There are several methods to do so:
-use structural program to develop influence lines and latter, knowing the position of the movable loads position the loads and calculate forces. This is the procedure for complicated bridges and rather laborious.
-Use any program with "movable loads" command. GT STRUDL and STAAD both have this feature. Be careful if the bridge is long and lane loading is used - both work fine only with the truck or AMV load (as per AASTHO) and do not recognize the change of sign within the span.
-Download from http://yakpol.net/ the spreadsheet to develop influence lines. Later use any method to calculate the forces. (There are also some spreadsheets calculating the envelopes, check these too)
-use any of the published moment and shear envelops for continuous beams. (And do not worry too much about the frame action of the piers - check the ratio of I's for spans and columns - usually is 1 to 5 - 10. In any case this will only increase your moments in the span, so may be you'll over design by few percent.

RE: Muti span bridge design moments


If you are truly a "non-structural" civil engineer, I strongly urge you to pass along any bridge calculations to an experienced bridge/structural engineer. Live loads can be very tricky to calculate and understanding the load combinations is also difficult.


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