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Effect of abutment modeling on the seismic response of
bridge structures

Ady Aviram ¹, Kevin R. Mackie ²  and Bozidar Stojadinovic¹

1. Department of Civil and Environmental Engineering, University of California, Berkeley
2. Department of Civil and Environmental Engineering, University of Central Florida

Abstract: Abutment behavior signiicantly inluences the seismic response of certain bridge structures. Speciically in
the case of short bridges with relatively stiff superstructures typical of highway overpasses, embankment mobilization and
inelastic behavior of the soil material under high shear deformation levels dominate the response of the bridge and its column
bents. This paper investigates the sensitivity of bridge seismic response with respect to three different abutment modeling
approaches. The abutment modeling approaches are based on three increasing levels of complexity that attempt to capture
the critical components and modes of abutment response without the need to generate continuum models of the embankment,
approach, and abutment foundations. Six existing reinforced concrete bridge structures, typical of Ordinary Bridges in
California, are selected for the analysis. Nonlinear models of the bridges are developed in OpenSees. Three abutment model
types of increasing complexity are developed for each bridge, denoted as roller, simpliied, and spring abutments. The
roller model contains only single-point constraints. The spring model contains discrete representations of backill, bearing
pad, shear key, and back wall behavior. The simpliied model is a compromise between the eficient roller model and the
comprehensive spring model. Modal, pushover, and nonlinear dynamic time history analyses are conducted for the six bridges
using the three abutment models for each bridge. Comparisons of the analysis results show major differences in mode shapes
and periods, ultimate base shear strength, as well as peak displacements of the column top obtained due to dynamic excitation.
The adequacy of the three abutment models used in the study to realistically represent all major resistance mechanisms and
components of the abutments, including an accurate estimation of their mass, stiffness, and nonlinear hysteretic behavior, is
evaluated. Recommendations for abutment modeling are made.

Keywords: embankment; backill; shear keys; bearing pads; nonlinear analysis