Diagnosis and Mitigation of Fatigue Damage in Longitudinal Diaphragms of Cable-Stayed Bridges

Abstract

Premature fatigue cracking in the tube-gusset plate connection of longitudinal diaphragms has been observed in long-span cable-stayed bridges, resulting in undesirable stress distribution of the decks and costly repair efforts. Based on field inspection and finite-element (FE) simulation, this paper presents a diagnosis of the fatigue damage, and it is found that under the vehicle loads the connections are subjected to large stress cycles and significant stress concentration exists around the cope holes. The secondary stresses caused by bending result in different degrees of cracking among the eight locations of the diaphragm within a chamber. To mitigate such damage, several retrofit measures, including plug welding at the slot end, crack-stop holes, welded plates, and bolted channels, were applied. According to field observation and FE simulation, it is found that although the plug welding, crack-stop holes, and welded plates may slightly mitigate the cracking, they cannot significantly elongate fatigue lives. The bolted steel channel connections, however, have an acceptable life without decreasing the stiffness of the diaphragms.