Field Evaluation of Fatigue Stresses in a Modern Highly Skewed Steel I-Girder Bridge

Abstract

Modern specifications require that connection plates on steel I-girders must be connected to both the flange and the web. While this modern connection detail undoubtedly reduces distortion-induced fatigue compared with past practice, it does not eliminate it. Because fatigue problems may take several decades to develop, the effectiveness of this detail is not fully known at present. Therefore, strain measurements were collected on the girders and cross-frames of a skewed I-girder bridge with modern connection details. This field testing was also used to validate a finite-element model to more thoroughly evaluate the fatigue response and perform a parametric study comparing different skews and inline versus staggered cross-frame configurations. The results support that the modern detailing guidance of using full-depth connection plates connected to both flanges to prevent distortion-induced fatigue is generally effective. The data also indicate three areas where additional consideration may be warranted with respect to modern detailing guidance: the use of a bent plate connection at highly skewed abutments, variable dynamic amplification effects with respect to distortion-induced fatigue, and the use of staggered cross-frames.