Geometric nonlinear behavior of cable-stayed bridges

Cable-stayed bridges have received more attention due to their ability to arch over large spans. As the bridge span increases, the high strength material have been used and the bridge becomes more flexible and, as a result, more susceptible to nonlinear behavior. The geometric nonlinear behavior of cable-stayed bridges are studied. Cable-stayed bridges with geometry similar to the Quincy Bayview Cable-Stayed Bridge under static and dynamic (traffic type loads) were studied. The subjects of this study include the following: (1) Two dimensional and three dimensional finite element models of cable-stayed bridges: In two dimensional finite element model, the pylons and the bridge deck were modeled as beam elements. The cables were modeled as truss elements. In three dimensional model, the pylons were modeled as beam elements. The bridge deck and the composite girders were modeled as shell elements and the equivalent dimension of the bridge deck and the composite girders were formed. (2) The nonlinearity effect in static analysis: The load-displacement curve of the pylons in the horizontal direction and the load-displacement curve of the bridge deck in the vertical direction were found. (3) Buckling influence lines: Tabular and graphical results were made by parametric study of cable-stayed bridges. (4) Cable stiffness: Cable nonlinear behavior and the effect of modified Young's modulus (E) of the cables in buckling analysis were studied. The buckling loads of the simple model of the cable-stayed bridge and the buckling loads of the finite element model of cable-stayed bridge were compared. (5) Cable preloading selection: Four different preloading methods were considered and the most effective method was found. (6) The effect of buckling load under different support conditions: Eight different support conditions were considered in this project. (7) The nonlinear effect on dynamic analysis: The axial force effect (bridge deck only) in dynamic frequency analysis under normal design load was estimated. The critical velocities in the velocity range between 20 MPH and 90 MPH were found. (8) Comparison of two dimensional and three dimensional analysis: The importance of the three dimensional analysis was estimated by comparison of the two dimensional and three dimensional buckling loads and buckling mode shapes.; In conclusion, criteria were established to determine the importance and necessity of the above mentioned nonlinearities in the analysis and design of cable-stayed bridges.