Railroad Bridge Load Rating

[jmag03]

I've load rated hundreds of highway bridges using AASHTOWARE BrR but have never rated a bridge that carries a railroad. I have several railroad bridges I would like to rate using BrR. They are simple span steel through girder with built-up sections and floorbeams on tangent alignments. The bridges are straightforward to model and I plan to add any additional loads for the ballast, track, catenary poles, fences, additional concrete from deck tubs, etc. I can create the trains as "trucks" defining the axle loads and spacing and the wheel pitch. I can then define the lane along the track location. I need to research calculation of LLDFs more and make sure that AREMA specifications are followed, but does anybody have experience using BrR to load rate railroad bridges? Is there anything I'm overlooking as to why these bridges would require another analysis software such as MIDAS? Any input is much appreciated. Thanks!

 

[BridgeSmith]

You'll most likely have to manually enter the distribution factors, which is the portion of the axle loads that's applied to a particular girder. If they're typical RR bridges, there's a girder under each rail, in which case the DF for each girder is 0.5. If there's more than 2 girders, it gets more complicated, because you have to figure out the stiffness of your transverse members to determine what portion of the load each girder carries.