Effect of Near-Fault Vertical Ground Motions on the Seismic Response of Bridges with Rocking Foundations

Abstract

Rocking foundations can be used in bridges to reduce the seismic demand of the structure and prevent inelastic behaviour from developing at the piers during large earthquake events. Several studies have proven that rocking is an effective seismic isolation technique under lateral earthquake loading. However, limited research has been conducted on the effect of the vertical component of earthquakes on the rocking behaviour of bridge piers. This paper aims to numerically investigate the effect of the vertical component of near-fault earthquakes on the seismic performance of bridges with rocking pile foundations. Two identical bridge configurations with different foundation systems (conventional fixed base foundation and rocking foundation) are subjected to two loading cases: (1) horizontal ground motions only, (2) combined horizontal and vertical ground motions. Three-dimensional models of the bridges are developed with the appropriate material models to capture possible inelastic behaviour, as well as to model the soil–structure interaction. Four near-fault ground motions with three components are selected and scaled to the appropriate seismic hazard and applied to the bridges using nonlinear dynamic time history analyses. The dynamic responses of the bridges are compared in terms of deck displacements, deck bending moments, and pier axial and bending moments. The results show that the vertical component of ground motions can considerably increase the dynamic response of the bridge with the rocking foundation when compared to the fixed base foundation, leading to increased deck displacements and inertial actions on the bridge structure.