Space Equivalent Truss Finite Element And Its Application

Space equivalent truss element is a new finite element model, which is used to analyze the space structure in finite element method. Complicated displacement field function is needed to build in traditional element types, and in nonlinear analysis of reinforced concrete structure, it is difficult to chose the constitutive models of concrete, also is difficult to handle the crack of concrete. A kind of space equivalent truss element is deduced in this paper, which extends the concept of plane equivalent truss elements. It is used to analyze the space structure and applicated to the analysis of reinforced concrete structure.Space equivalent truss element is composed of eight hinge points and twenty four two-force bars. Each bar in the element is only subjected to axial force, and three dimensional stress-strain state is converted to one dimension in this model, also this model doesn’t need complex displacement field function and its stress is clear. With these features, in nonlinear analysis of reinforced concrete structure, uniaxial constitutive relation can be adopted and crack expansion in concrete can be simulated in light of crack order of bars, which is easy to deal with.Main research achievements in this paper are as follows:(1) Space equivalent truss element is obtained based on the concept of plane equivalent truss element, and it is used to solve space problems.(2) With equivalent analysis, parameter of each bar in this kind of element is deduced and stiffness matrix expression of the element is obtained.(3) A source programme of this element is compiled and used to analyze a freely supported beam, a cantilever beam and a column.(4) This new element is applicated to nonlinear analysis of reinforced concrete structure. With the character of this element, suitable constitutive relation and calculation mode are selected, and a new cracking model is proposed to solve the crack simulating problem, in which the bars’crack order is used to simulate the crack of concrete. The new element is utilized to simulate the loading process of a reinforced concrete bridge pier, the results are compared with results of experiment method and technical code design method, and get the crack expansion in concrete with the cracking model of this paper.