Service Behavior Of Steel-Concrete Composite Box Beams And Triaxial Nonlinear Analysis

Based on the mechanics of continuous media, mechanics of thin-walled structure and the theory of nonlinear finite element analysis, the overall service behavior of steel-concrete composite box beams are analyzed comprehensively. A new finite element for steel-concrete composite box beams and a theoretical computing meathod are set up. Three samples of composite box beam are tested. The influences by different factors are researched and an expression for bearing capacity influence coefficient is set up. The main contents are listed as follows:(1)A variational method taking slip and dual effects of slip and shear deformation into consideration is presented. The associated differential equation of deformation and slip are deducted by the theory of minimum potential energy. The expressions for deformation and slip of composite box beams are obtained. The method is simple and explicit in physical meaning and lays a foundation for finite element analysis, that the slip and shear deformation can be easily calculated by the matrix displacement method used widely.(2)Based on the behaviour characteristics of composite box beams, a new triaxial nonlinear finite element for composite box beams with slip effect is presented. The main idea is that the stubs are regarded as a layer of continuous medium and the slip deformation is distributed to steel beam and concrete board according to slip deformation model. By the method, the deformation model for composite box beams regarding slip and shear deformation can be obtained. Based on the theory of minimum potential energy, the element stiffness matrices, vector of externally applied element nodal loads, vectors of nodal point force are formed.(3)Based on the triaxial nonlinear finite element theory for composite box beams, a nonlinear analysis program for composite box beams is worked out. The result shows that, the element is reliable and easy to use and divide and is suit for special nonlinear analysis of large-span composite box beams.(4)Three samples of simple-supported composite box beam are tested, including elastic state and limit state. The working performance,including deformation, strain, slip and so on, are obtained. The limit state modes and the influencing factors are analyzed. The tested results have a good degree with the calculated results, which show the slip-deformation variation method and the finite element method is accurate and reliable.(5)A series of composite box beams, with different degrees of shear connection, web's ratio of height and thickness, force ratio and initial degree of non-plane, are simulated with the nonlinear analysis program. The laws of bearing capacity, deformation, and slip of composite box beams with different parameters are obtained. A expression for bearing capacity influence coefficient is obtained, which is important reference for improving the code of steel-concrete composite structure.