A Critical Fatigue Crack in a Long-Span Truss Bridge; Cause Investigation and Measures

This paper presents a report on a critical fatigue crack in a long-span truss bridge and a series of measures from cause investigation to preventive retrofit for the damage. The severe damage occurred and propagated due to a fatigue crack at the bottom of a diagonal member of the bridge. The findings obtained by the web-based long-term monitoring reveals that the member being mainly investigated and the other several diagonal members have excited in two wind velocity ranges. Wind directions of both the case are approximately perpendicular to the bridge axis. Componential analysis of vibration suggests that in-plane vibrations are vortex-induced and vibration out-of-plane is buffeting due to strong wind. The vibration induced by the strong wind was the main cause of the crack. Based on the findings, a preventive measure has been taken to suppress wind-induced vibration by changing the dynamic characteristic of diagonal members.