NONLINEARITIES IN CABLE STAYED BRIDGES

Abstract

The cable-stayed bridge is the most modern and innovative of the bridge systems. It has found world-wide applications, especially in European countries during last four decades. A cable-stayed bridge is a nonlinear structural system in which the girder is supported elastically at points along its length by inclined cable stays. Even if the material in the members of a cable-stayed bridge behaves in a linear elastic manner, the overall load-displacement relationships for the structure will be nonlinear under normal design loads. Therefore, a nonlinear analysis is essential for evaluating stresses and deformations induced by gravitational loads and also for assuring safety during construction. In the present work finite element method has been used to analyse a cable-stayed bridge. For this purpose an analysis software which uses iterative method of nonlinear analysis • has been developed. A model cable-stayed bridge with two unequal spans has been considered for the present study for symmetrical and unsymmetrical support conditions considering nonlinear effects due to cable sag, beam-column interaction, geometric change and combination thereof. The structure has been analysed for a uniformly distributed live load over the entire span. From the analysis it has been observed that the effect of geometric change is much more compared to the effects due to cable sag and beam-column interaction. It is also observed that there is a marked change in deflections, bending moments and axial forces in tower and deck, whereas the cable tensions are affected by a maximum of 2.3 % due to geometric nonlinearity. In addition to the above linear analysis for secondary effects due to temperature, shrinkage and creep has also been carried out. In addition to this a graphics software in AUTOLISP as a post processor has been developed to draw the 3 dimensional geometric configuration of cable-stayed bridge both in the deflected and undeflected shapes.