Field Evaluation of Cross-Frame and Girder Live-Load Response in Skewed Steel I-Girder Bridges

Abstract

A better understanding of the relationships among girder stresses, cross-frame design, and skew angle of two steel I-girder bridges, which have moderate and high levels of skew and differing cross-frame designs, was revealed via field testing under various load passes of a weighed load vehicle. Strains were measured at approximately 100 points on the two structures, and the majority of the instrumentation was located on the cross-frames. The data were analyzed in terms of vertical bending, lateral bending, and warping in the girders, and in the magnitudes and distribution of stresses in the cross-frames of the two structures. These metrics were compared between the two bridges and in relation to the assumptions typically used in contemporary bridge analysis. This comparison revealed the following: the magnitudes of lateral stresses were higher than current design guidance suggests in some cases when staggered cross-frames were used; significant magnitudes of warping stresses in the girder webs, which state-of-the-art analysis methods generally fail to consider; and cross-frame stresses that exceeded the values typically considered in design.