A 3D nonlinear static analysis of long-span cable stayed bridges

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A numerical investigation on the nonlinear static behavior of self-anchored long span cable-stayed bridges with a fan-shaped arrangement of stays is carried out by adopting a spatial finite element model of the bridge. An equivalent continuous model of the bridge is also developed in order to point out the main parameters governing the non-linear behavior of the bridge to be used in the more general 3D discrete bridge analysis and to provide a validation of the discrete model. The importance of an accurate description of geometrically nonlinear effects arising from the stays nonlinear response in coupling with the instability effect of axial compression in girder and pylons, is evaluated by means of original comparisons with results obtained by using simplified assumptions. Novel parametric studies are performed for investigating the influence of the main geometrical and material design parameters derived from the continuous model formulation on the maximum load-carrying capacity of the bridge and related collapse mechanisms. Different loading conditions, also including live load eccentricities, and pylon shapes are also considered and a nonlinear procedure for finding the initial geometry and prestress distribution under dead load is incorporated in the analysis. The results point out the strong role of nonlinear stays response, especially when the assumed loading condition produces cable unloading, in coupling with the notable influence of the relative girder stiffness on the stability bridge behavior. On the contrary, in general pylon shape and stiffness, live load eccentricity and torsional stiffness are less important factors in non-linear analysis.