Collapse of Showa Bridge Revisited

Abstract

The collapse of the Showa Bridge during the 1964 Niigata earthquake features in many publications as an iconic example of the detrimental effects of liquefaction. It was generally believed that lateral spreading was the cause of failure of the bridge. This hypothesis is based on the reliable eye witness that the bridge failed 1 to 2 minutes after the earthquake started which clearly ruled out the possibility that inertia (during the initial strong shaking) was the contributor to the collapse. Bhattacharya (2003), Bhattacharya and Bolton (2004), Bhattacharya et al (2005) reanalyzed the bridge and showed that the lateral spreading hypothesis cannot explain the failure of the bridge. The aim of this short paper is to collate the research carried out on this subject and reach conclusions based on analytical studies and quantitative analysis. It is being recognised that precise quantitative analysis can be difficult due to lack of instrumented data. However, as engineers, we need to carry out order-of-magnitude calculations to discard various failure hypotheses.