Ultimate Strength and Chain-Reaction Failure of Hangers in Tied-Arch Bridges

This study was motivated by the recent collapse of a tied-arch bridge with branched arch ribs. Hangers were successively broken when a heavy lorry crossed the bridge. In this article, the ultimate strength of tied-arch bridges, causes of hanger rope breakage and simulation of chain-reaction failure of hangers are studied for tied-arch bridges. Nonlinear finite element method analysis has clarified that this bridge model has sufficient ultimate strength. The hanger arrangement significantly affect the ultimate strength. The model with uniformly distributed hangers has higher ultimate strength and the hanger tensions are well balanced. Corrosion fatigue of wires could cause hanger rope breakage. The stress amplitude would be further amplified by secondary bending stresses, different safety factors, improper hanger tensions due to poor quality control, impact factors induced by moving vehicles, and effects of other vehicles. As the fatigue strength of corroded strands is significantly decreased, the estimated stress amplitude could cause hanger breakage. When a hanger breaks, the dead and live loads work impulsively, which are replaced by the equivalent static loads. The load is redistributed to the hanger next to the broken hanger, which induces the chain-reaction failure of hangers. This simulation method clarifies the mechanism of the bridge collapse.