Seismic Re-qualification of Caisson Supported Dhansiri River Bridge

Abstract

There are multitudinous major river bridges in India which were built prior to the development of seismic codes and it is very difficult to predict the performance of those bridges during earthquake. Since bridges are the lifeline structures, it is essential to requalify these structures in light of the new and better understanding of seismic resistant design philosophies. This paper aims to carry out a requalification study of an important river bridge supported on caisson foundations (or Well Foundations). Field investigation and laboratory tests on soil samples from the bridge site are carried out and the data achieved are used as input values for the soil model. Two different types of earthquakes, each having different dynamic properties are considered for the study. The effective stress site response analysis is carried out and the liquefaction potential of the bridge site is evaluated. Analysis revealed that a large number of the soil layers are liquefied under the applied earthquake motions. Considering the liquefied soil, seismic analysis of the bridge is carried out. The seismic analysis gives the damage levels in terms of bending moments and displacements of the well foundation. The moment of resistance of the well section is calculated and the maximum bending moments under the considered earthquakes are checked with the moment capacity of the well. It is found that the well is safe under both the earthquakes. Hence, no strengthening or retrofitting strategies of the bridge structure are required for this study.