Rapid Assessment and Decision Making Strategies for Distortional Fatigue Multi-Girder Steel Bridges

Project summary:

Multi-girder steel bridges are found as part of the transportation infrastructure of countries throughout the world. These bridges are typically constructed with a steel reinforced concrete deck rigidly attached to the top flange of steel girders. The deck and the transverse steel members distribute loads laterally between bridge girders. The weld connecting transverse stiffeners to the girder web are commonly terminated several inches away from the girder flanges to avoid overlapping with the web-to-flange connection weld, leaving a short, unstiffened portion of the girder web--the web gap. The large flexibility of the web gap region relative to the other components forces it to accommodate the majority of the distortion. Since 1998, several research efforts have investigated methods for predicting the amount of web gap stress a bridge will experience during its service life. Phase I of this research resulted in a simple equation for estimating web gap stress using data collected during field testing and subsequent finite modeling of a skew supported bridge with staggering bent-plate diaphragms. Phase II produced an approximate method for predicting diaphragm differential deflection of skew supported bridges with bent-plate diaphragms. The combined result of Phase I and Phase II was a useful method for predicting peak web gap stress in skewed multi-girder steel bridges with staggered bent-plate diaphragms. The next step was to develop a reliable procedure for the rapid assessment of distortional stresses in steel bridges that includes a test of the applicability of this procedure to bridges with geometries differing from those that formed the basis of the previous research. As a consequence of this most current research, the authors propose changes and recommend modifications of previously developed methods of field measurement and assessment.