Investigation of the Cause of Failure of the Omo River Bridge

Abstract

The reason for the failure of the Omo River Bridge that collapsed and partially sank into the river during construction was investigated using standard, structural and analytical finite element model (FEM) and design review procedures according to Eurocode 3. The bridge was initially constructed by a launching construction technique. The span design was based on a Callender-Hamilton bridge type with Warren trusses of the D8M type classification. In all 40 stages were required to put the bridge in place. The bridge collapsed and partially sank into the river during construction, between stages 34 and 35. From in situ inspection, it was observed that the main bridge did not show any significant distress. Moreover, the mode of failure suggested a weak link between the main bridge and the launch nose. The results of the investigation showed that the diagonal link angles in the critical region where the main truss was connected with the launching nose were found to be the most critically loaded members. These members were stressed to their ultimate limit state, causing them to buckle and trigger the sudden collapse of the bridge at the end of launching stage 34.