Nonlinear Seismic Response Analysis of Curved and Skewed Bridge System with Spherical Bearings

A three-dimensional (3D) modeling approach to investigate nonlinear seismic response of a curved and skewed bridge system is proposed. The approach is applied to a three-span curved and skewed steel girder bridge in the United States. The superstructure is modeled using 3D frame elements for the girders, truss elements for the cross-frames, and equivalent frame elements to represent the deck. Spherical bearings are modeled with zero-length elements coupled with hysteretic material models. Nonlinear seismic responses of the bearings subjected to actual ground motions are examined in various directions. Findings indicate that the bearings experience moderate damage for most loading scenarios based on FEMA seismic performance criteria. Further, the bearing responses are different for the loading scenarios because of seismic effects caused by interactions between excitation direction and radius of curvature. 1. Introduction Studies related to the design and analysis of curved and skewed steel bridges have focused on modeling and design for static and pseudo-static loads [1–4], and only a few investigations have looked at seismic behavior [5]. To design and assess curved steel bridges in high and moderate seismic zones, it is of interest to more extensively examine seismic analysis methods so that reliable 3D modeling approaches are developed. Studies have been undertaken that applied modeling approaches to predict the seismic response of straight steel girder bridges [6]. Similar simplified modeling approaches have been proposed for curved steel bridges, but the approaches were applied to static events [1]. These studies have shown that modeling using a 3D approach can provide improved accuracy relative to line girder analyses by incorporating member depths. For a curved and skewed bridge, where significant lateral displacements may be induced at the bearings under a seismic event, modeling structural component depths would be assumed to be important. For these reasons, a 3D modeling approach is used herein to investigate seismic responses of a curved steel I-girder bridge system with skewed supports. The 3D approach is applied to a three-span continuous curved steel I-girder bridge system in the United States. Following the approach recommended by previous research [1], the bridge is modeled using elastic frame elements for the I-girders, truss elements for the cross-frames, and elastic frame elements for the deck. Preliminary seismic responses at the bearings are presented for the bridge under El Centro ground motions. 2. Modeling Approach All elements