EXPERIMENTAL GLOBAL–LOCAL NONLINEAR RESPONSE OF FOUNDATION–SUPERSTRUCTURE UNDER SEISMIC LOADING

Abstract

Nowadays, as the expected earthquake motions become significantly larger, the ultimate seismic performance of large foundations, such as the caisson foundation, needs to be investigated. This study examines the seismic response of a caisson foundation connected to a superstructure modeled as a single-degree-of-freedom system. This study focuses on the inertial effects and nonlinear soil-structure interaction of the entire system under four simulated earthquake records with varying amplitudes. In particular, attention is given to soil nonlinearity (yielding and failure) and interface nonlinearity between the soil and the caisson surface in contact with the soil. These factors may influence the inertial system of soil-caisson-superstructure in terms of its resonant period and damping characteristics. To investigate the seismic response under 1g condition, a 1/40 scaled model of a caisson foundation and superstructure is used, with a diameter and height of 350 mm and 500 mm, respectively.  The effects of soil and interface nonlinearities on the stiffness and damping of the superstructure interacting with the soil are evaluated using transfer functions, phase differences, pressure responses, and mean shear strain. Furthermore, the study examines the potential shift in dominant vibration modes, such as increased rocking motion of the caisson foundation with larger loading amplitudes. This research highlights the significance of soil and interface nonlinearities on the inertial behaviour of the soil-caisson-superstructure system under stimulated earthquake ground motions.