On the fundamental period of bridge piers on caisson foundations

抄録

Seismic behaviour of caisson foundations supporting bridge piers has been attracting the interest of researchers over the last few years, mainly due to their complex interaction phenomena with the soil and the superstructure, usually referred to as Kinematic and Inertial Interaction effects. Such embedded, rigid, and very large foundations are typically resorted to when dynamic horizontal forces generated by strong earthquakes are to be resisted. One of the main parameters influencing the Dynamic Soil-Structure Interaction of such structures is the fundamental, compliant-base period, T_eq. In this paper, the fundamental period of caisson foundations supporting bridge piers is computed from the results of dynamic centrifuge tests performed on reduced-scale models at University of Cambridge, UK. A rigid and a flexible bridge pier founded on a cylindrical caisson foundation, embedded in a typical alluvial deposit, were reproduced. The two systems were subjected to a series of both sine waves and acceleration time histories from ground motion records. The analysis of the experimental data allowed to estimate the fundamental period of the system, which was then compared with those resulting from relationships available in the literature. It is shown that the empirical equations may be profitably used at a preliminary design stage, provided that nonlinear soil behaviour, bringing the soil stiffness to decay during the seismic event, is considered.