TECHNIQUE ENABLES FLATCAR BRIDGES TO ATTAIN HIGHER LOAD RATINGS

Some states are using railroad flatcars in place of slab and girder superstructures for highway bridges on lightly travelled routes. Many agencies, including the Wyoming Department of Transportation (WYDOT), have opted to construct the flatcar bridges; however, rating procedures of the American Association of State Highway and Transportation Officials (AASHTO) are inappropriate for these complex superstructures, leaving agencies to rate these bridges for relatively low loads. This article describes a WYDOT integrated approach to evaluate the flatcar superstructure, which consists of comparing actual live load responses measured in the field to computer generated theoretical responses. Variations in responses are quantified, modelling parameters are modified, calibrated rating loads are applied, and rating factors are calculated. The integrated technique has allowed the posting limits of flatcar bridges to be increased, where appropriate.