The collapse of the Schoharie Creek Bridge: a case study in concrete fracture mechanics

Abstract

On April 5, 1987, the New York State Thruway bridge over Schoharie Creek collapsed without warning. The primary cause of failure was scour beneath a plain concrete pier footing. However, a necessary secondary cause was unstable propagation of a single crack in the pier. Conditions for initiation of the curvilinear crack are first evaluated. It is concluded that about 28 feet of scour had to occur to initiate stable process zone formation at the point of initiation, but that at least 44 feet was required to cause unstable cracking. Simulation of propagation was studied using discrete representation in a finite element model and nonlinear fracture mechanics. About 5 feet of propagation was necessary to transition from nonlinear to LEFM. Good agreement was found between observed and predicted final crack trajectories, and load redistribution in the bridge structure was determined to have been a necessary part of the failure process. Discussions concerning the application of the finite element method to crack initiation problems and the use of the size effect to estimate failure conditions in large, plain concrete structures are also presented.