Research On Nonlinear Theory And Load Carrying Capicity Of Cable Stayed Bridges

The main purpose of the work presented in this dissertation is to study the nonlinear theory and the load-carrying capacity of the cable stayed bridges, Algorithms are put forth about the problem of geometric and material nonlinear problems of the beam, cable shell and solid element.Several constitutive models are applied in the material nonlinear analysis of the structure, allowing for the hardening and softening effect in the stress-strain curve of the material. The meshed sectional beam-column element basis on the distributed plastic theory is presented, in which the sections of the beam are meshed at the numerical integration points along the longitudinal axis of the beam and the distribution of the stresses of the cross-section is described by interpolation through the stresses at the integration points. This method is advantage over the fiber beam-column element in both the computational efficiency and accuracy. The flexibility based method is also combined in this element, in which the force interpolation functions are used to describe the internal forces of the element so that the the equilibrium of forces along the element and deformational compatibility are both satisfied strictly. The contribution of the steel bar and concrete on the stiffness are counted in the analysis of the reinforced concrete structures respectively for nonlinear analysis of reinforced concrete structures, the effect of the movement of the neutral axis due to the crack of the concrete is also included in the computational procedure. The material constitutive models based on the multi-axial strength theory are introduced in the material nonlinear finite analysis of the shell and solid.The corotational formulation of the beam based on the "geometrically exact" theory is introduced in the geometric nonlinear analysis of the beam. The geometric and material nonlinear analysis is implemented by using the meshed section beam-column element with corotational formulation. Also, the Element Independent Corotational procedure is applied in the analysis of the shell and solid element to handle large rations, in which the Updated Lagrangian formulation is used to build the equation of equilibrium and the contribution of the rigid body motion of the element to the total displacement field is removed before element computations are performed.The finite element method is performed to solve warping functions equations, along with the numerical intergration approach to get the cross-sectional properties with arbitrary shape of the beam.Several kinds of cable element are used in the analysis of cable structures, bisection method is introduced in the evaluating the unstressed length of catenary element and shows the numerical stability.A modified arc-length method is discussed for passing the limit points in nonlinear structural analysis. A technique is present to improve the effectiveness of the arc-length method by overcoming the complex root problem.Based on the theory proposed in this dissertation, a nonlinear structural analysis program-BRANSYS based on the object-oriented programming (OOP) paradigm and generic programming (GP) pattern is developed.Several examples about the material and geometrical nonlinear analysis as well as the buckling analysis of the structures are given with the BRANSYS to testify the correction of the theory in the dissertation, the discussion about structural stability problem is also given. Finally, the load-carrying capacity of shaximiao bridge is evaluated under 4 load cases. The suggestion of the evaluation of safety of the bridge is given.