Ultimate Behavior of Long-Span Cable-Stayed Bridges

Abstract

The study described here investigates the nonlinear static and ultimate behavior of a long-span cable-stayed bridge up to failure and evaluates the overall safety of the bridge. Both geometric and material nonlinearities are involved in the analysis. The geometric nonlinearities come from the cable sag effect, axial force-bending interaction effect, and large displacement effect. Material nonlinearities arise when one or more bridge elements exceed their individual elastic limits. The example bridge is a long-span cable-stayed bridge of a 605 m central span length with steel box girder and reinforced concrete towers under construction in China. Based on the limit point instability concept, the ultimate load-carrying capacity analysis is done starting from the deformed equilibrium configuration due to bridge dead loads. The effects of the steel girder hardening and the girder support conditions on the ultimate load-carrying capacity of the bridge have been studied. The results show that the geometric nonlinearity has a much smaller effect on the bridge behavior than material nonlinearity. The overall safety of a long-span cable-stayed bridge depends primarily on the material nonlinear behavior of individual bridge elements. The critical load analysis based on the bifurcation point instability concept greatly overestimated the safety factor of the bridge. The ultimate load-carrying capacity analysis and overall safety evaluation of a long-span cable-stayed bridge should be based on the limit point instability concept and must trace the load-deformation path of the bridge from applied loads to failure.