On the beneficial role of pile and soil inelasticity on the seismic performance of bridge piers

Abstract eng:
While seismic codes do not allow plastic deformation of piles, the Kobe earthquake has shown that limited structural yielding and cracking of piles may not be always detrimental. As a first attempt to investigate the consequences of pile yielding in the response of a pile–column supported bridge structure, this paper explores the soil–pile–bridge pier interaction to seismic loading, with emphasis on structural nonlinearity. The pile-soil interaction is modeled through distributed nonlinear Winkler-type springs and dashpots. Numerical analysis is performed with a constitutive model (Gerolymos and Gazetas, 2005a; 2005b; 2006a) materialized in the OpenSees finite element code (Mazzoni et al, 2005) which can simulate: the nonlinear behaviour of both pile and soil; the possible separation and gapping between pile and soil; radiation damping ; loss of stiffness and strength in pile and soil. The model is applied to the analysis of pile-column supported bridge structures, focusing on the influence of soil compliance, intensity of seismic excitation, pile diameter, above–ground height of the pile, and above or below ground development of plastic hinge, on key performance measures of the pier as is: the displacement (global) and curvature (local) ductility demands. It is shown that both pile and soil inelasticity may be beneficial for the performance of the superstructure. Moreover, kinematic expressions for performance measure parameters may lead to erroneous results when soil–structure interaction is considered.

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