ABSTRACT
The soil structure interaction in case of liquefied soil is not completely understood. As a result, it has been recurrently observed that the middle piers of the pile supported bridges fail in case of liquefaction while the abutments and its adjacent piers remain stable. The current paper proposes a mechanism behind such collapses. It is well-known that the natural periods of the piers increases as the soil liquefies. Due to the inherent river bed profile, the natural period of the central pier increases more as compared to the other ones. Correspondingly, the displacement demand for the central piers increases more. Hence, if the seating length is inadequate, the spans may fall off the piers due to this differential displacement demand. A case study of failure of Showa Bridge has been provided to corroborate this mechanism. It has been observed that the displacement demand for the central piers increased by more than 200% for the central piers, while for the piers close to the abutment it increased by just 50–60%.
