Repair of Steel Bridge Girders Damaged by Distortion-Induced Fatigue

Abstract

Several studies have identified distortion-induced fatigue as the leading cause of cracks in steel bridges built prior to the mid-1980s. Experimental and computer simulations of 914-mm (36-in.) deep girder-cross frame subassemblies subjected to cyclic loading were carried out to study the effects of distortion-induced fatigue and to evaluate the effectiveness of various retrofit measures. Previous repair methods for distortion-induced fatigue damage have attempted to reduce the stress demand at the critical web-gap region by increasing the flexibility of the girder web in the out-of-plane direction or by restraining the lateral motion of the web by fixing the connection stiffener to the girder flange. A new approach was investigated in this study intended to reduce the stress demand in the web-gap region by re-distributing the out-of-plane force transferred through the girder-cross frame connection over a larger area of the girder web. A new retrofit measure is proposed based on this approach, which consists of adding steel angles connecting the girder web and the connection plate (CP), and a steel plate on the back side of the girder web to distribute the lateral force over a wider region of the web. Experimental and computer simulation results are presented showing that this repair method is very effective in preventing the growth of horseshoe-shaped cracks around the web cross-frame connection and of horizontal cracks near the junction between the flange and web.