Steel Truss - Concrete Composite Beam Space Finite Element Analysis

The steel truss-concrete composite beam, in which the concrete plate and steel truss co-act together, has come into use in long span bridges because of its many advantages, But no simple and efficient analysis method is suitable for this kind of structure at present. So triaxial finite element theoretical analyses on the steel truss-concrete composite beam is carried on in this paper. The triaxial displacement model is proposed, a new finite element for steel truss-concrete composite beam and a theoretical computing method are set up. Different influencing factors are researched. The main contents are listed as follows:(1)A new finite element for steel truss-concrete composite beam with slip effect is proposed. Steel truss chord node displacement is elected as element displacement parameter directly in this paper. To consider the slip effect, longitudinal slip degree of freedom, coupled with longitudinal displacement of beam, is set up between steel truss and concrete plate. The element can analyze the local bending deformation of plate by introducing transverse finite strip elements of concrete plate, and the effect of uneven longitudinal deformation of concrete plate by introducing multiple parameter displacement function of shear lag warping deformation. Based on the thoughts that the total displacement of particles is the sum of the displacements caused by global and local deformation, the displacement model and calculating formulae are formed.(2)Based on the behaviour characteristics of composite truss and the theory of nonlinear finite element, a new triaxial finite element for steel truss-concrete composite beam with slip effect is presented. By the method, the deformation model for steel truss-concrete composite beam 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. Considering material nonlinear, nonlinear finite element analysis method for steel truss-concrete composite beam is set up.(3)Based on the triaxial finite element theory for steel truss-concrete composite beam, an analysis program for steel truss-concrete composite beam is worked out. According to the computing results obtained from existing experiment, the correctness of the mechanics methods, analysis model and calculating program in this dissertation is proved. The result shows that the element is reliable, easy to use and divide and suit for special nonlinear analysis of long-span steel truss-concrete composite beam.(4)A series of steel truss-concrete composite beams, with different depth-width ratio, stiffness of web member and degrees of shear connection, are simulated with the analysis program. The laws of deformation, stress, and slip of steel truss-concrete composite beam with different parameters are obtained.