Dynamic soil-structure interaction of bridge-pier caisson foundations

This paper presents the main results of 3D FE dynamic analyses carried out in the time domain to assess the seismic performance of rigid and massive circular caisson foundations supporting bridge piers. Various foundations systems are subjected to a real acceleration time history. Soil behaviour is described by an elastic-plastic model capable to provide a fair estimate of nonlinear soil behaviour and hysteretic damping under cyclic loading conditions. The coupled dynamic analyses are carried out in terms of effective stresses, thus evaluating the excess pore water pressures induced by earthquake loadings. Caisson construction stages are reproduced in a simplified way. The influence of pier height and caisson slenderness on maximum and permanent displacement and rotation attained during and at the end of the seismic shaking is considered. The equivalent seismic coefficient to be adopted in a pseudo-static analysis to check the safety of the foundation against geotechnical limit states is also evaluated.