Fatigue Assessment of Through Plate Girder Railway Bridges

The behavior of two through plate girder railway bridges were investigated to determine a better approach to fatigue assessment. One bridge, a 21.3-m span near Old Fort, North Carolina, was instrumented, and measurements of member strains and deflections were taken during the crossing of a work train. These measurements were used to calibrate a parametric study of the modeling of this bridge structure and the applied loading to the structure. The second bridge, a 12.2-m span in Vonore, Tennessee, was analyzed using the same modeling developed for the first bridge to determine the differences between the responses of these two span lengths when subjected to similar traffic patterns. From the results of this study two conclusions were drawn: (1) the response of plate girders is controlled more by axle spacings than by axle loads; and (2) the influence of track structure interaction and bridge floor system continuity during analysis is crucial to accurately assessing maximum stresses or number and magnitude of stress cycles. More importantly, the analysis technique presented in this paper provides a better and more favorable prediction of the actual stresses experienced by a bridge during the crossing of a train.