3‐D Nonlinear Seismic Behavior of Cable‐Stayed Bridges

Abstract

The dynamic behavior of three‐dimensional (3‐D) long‐span cable‐stayed bridges under seismic loadings is studied. The cases of synchronous and nonsynchronous support motions due to seismic excitations of these flexible structures are considered; furthermore, effects of the nondispersive traveling seismic wave on the bridge response are studied. Different sources of nonlinearity for such bridges are included in the analysis. Nonlinearities can be due to: (1) Changes of geometry of the whole bridge due to its large deformations, including changes in the geometry of the cables due to tension changes (known as the sag effect); and (2) axial force and bending moment interaction in the bridge tower as well as the girder elements. A tangent stiffness iterative procedure is used in the analysis to capture the nonlinear seismic response. Numerical examples are presented in which a comparison is made between a linear earthquake‐response analysis (based on the utilization of the tangent stiffness matrix of the bridge at the dead‐load deformed state) and a nonlinear earthquake‐response analysis using the step‐by‐step integration procedure. In these examples, two models having center (or effective) spans of 1,100 ft (335.5 m) and of 2,200 ft (671 m) are studied; this range covers both present and future designs. The study sheds some light on the salient features of the seismic analysis and design of these long contemporary bridges.