Seimic analysis of cable-stayed bridges

During the last decades, cable-stayed bridges have gained a wide reputation. With the increasing central span length of modem cable- supported bridges, and consequently, the carrying capacity of structural elements, deflection and cable tension forces under service and earthquakes loadings, the demand of accurate analysis considering the geometric nonlinearity is highlighted. Different sources of geometric nonlinearity in the analysis of cable stayed bridges are contributed through three factors: changes in the geometry of the cables due to tension changes (sag effect), axial force- bending moment interaction on tower as well as the girder elements, and finally the change of geometry of the whole bridge due to large displacements. Previous studies show that, for intermediate span, linear dynamic analysis is adequate but nonlinear static analysis under dead loads is still essential to start the linear dynamic analysis from the dead load deformed state. In this thesis, a finite element computer program was developed to study simultaneously the effect of these sources of non-linearity on the behavior of cable-stayed bridges under gravitational and seismic loading. This program is used to recognize the importance and the participation factor of each parameter on the overall response of this type of bridges. The thesis explains also, the effect of dead load stiffness and cable pretension on the dynamic analysis. Two hypothetic conventional cable-stayed bridges are used through the analysis to represent both the present and future trends in cable-stayed bridge design.