Practical dynamic analysis model of rocking foundations under earthquake excitation

Abstract

Abstract To assess the performance of a structure with spread footings under seismic loading, considering the rotation and settlement of the footings caused by rocking is essential. Based on the beam-on-a-nonlinear Winkler foundation model, this study develops a practical approach to simulate the seismic responses of bridge columns with spread footings, including the footing settlement and rotation and the accelerations of the structure, by employing structural elements that are readily available in most commercial structural analysis software. To effectively simulate the footing settlement behavior, the nonlinear backbone curve and load-unloading stiffness of vertical springs for the foundation soil are crucial. These are determined based on plate load testing. The proposed approach was verified by simulating a single column-footing model under different excitation histories in shaking table testing. The results were in reasonable agreement with the actual measurements. Parametric studies were conducted to explore the characteristics of the proposed model, including calibration of subgrade stiffness with plate load testing, unloading stiffness of soil, system frequency and viscous damping ratio for the dashpot damping coefficient, and types of hysteretic models.