Fracture Analysis of King's Bridge, Melbourne

The fracture of the King's Bridge at Melbourne (1963) is of special interest because the responsible prior cracks were carefully photographed and the failure load can be estimated. With the aid of fracture mechanics and structural analysis, the critical crack size and failure load are compared with fracture toughness data for a steel regarded as comparable in toughness to that used in the Melbourne bridge. The results imply that rapid crack propagation developed when the tensile force on the crack was increased to a value intermediate between the crack propagation resistances expected for rapid (impact) and for slow loading. Structural redundancy of the Melbourne bridge allowed the bridge to provide continued service for 12 months after one of the four supporting girders suffered a major fracture. It is suggested that analysis of expected crack sizes and fracture toughness can be used to estimate the degree of fracture fail-safe behavior potentially present in steel bridges.