Civil Engineering Association

FAILURE OF SHOWA BRIDGE DURING THE 1964 NIIGATA EARTHQUAKE: LATERAL SPREADING OR BUCKLING INSTABILI TY

Following the 1964 Niigata earthquake many bridges, including the Showa Bridge, over the Shinano river collapsed. The newly-constructed Showa Bridge demonstrated one of the worst instances of damage, and there are still uncertainties and controversies regarding the causes of collapse. The collapse of the Showa Bridge has been, throughout the years, an iconic case study for demonstrating the devastating effects of the lateral spreading of liquefied soil. In this paper, this widely accepted collapse hypothesis has been challenged. The documented eyewitnesses’ observations and post-collapse damage reports have been reanalysed, and the all the major studies on the collapse of the bridge compared and contrasted. It has been shown that the current, widely accepted,
failure mechanism based on bending due to lateral spreading, cannot explain the failure. This paper presents a new hypothesis based on buckling failure due to axial loads in conjunction with residual, earthquake-induced, lateral displacements. This alternative explanation has been evaluated quantitatively using the method suggested by Kerciku et al. (2008) for estimating the buckling capacity of piles in liquefied soil, and Eurocode 3 (1993) recommendations for steel members subjected to bending and axial compression.