Research On The Finite Element Method Of Equivalent Plane Truss Element

Structural analysis plays a key role in the engineering design. Both infinite element method and traditional finite element method (FEM) have defects. The former can only resolve limited elasticity problems, while the latter can be used in much available situations. But it is more difficult to build displacement interpolating function and process huge data in FEM, the analysis results are always unstable in plasticity phase of material nonlinear. Aiming at plane stress problem, based on the stress-strain analysis of micro-unit and the thought of FEM, thispaper construct a novel element -- equivalent plane truss element. The approximatecalculation method realizes a simple and utilitarian solution to complicated two-dimension problems under tantamount precision. Further, this kind of element is applied in nonlinear analysis of reinforced concrete(RC) structure and the equivalent plane truss element model of RC structure is proposed in the paper. Abundant examples prove that the method is applicable which can be referenced by in engineering.Firstly, focusing on plane stress problems, the paper construct equivalent plane truss element, which converts complex two-dimension problems to one dimension problems. There are only axial force link elements in the new model under nodal loads, thus the internal force and deformation of elements becomes simple and explicit to be calculated and judged easily. Furthermore, it can meet the requirements of engineering precision.Secondly, the equivalent plane truss element analysis program of plane stress problem is worked out, by which cantilever beam, simple beam and perforated wall are analyzed. The calculation results and other results of traditional FEM are consistent.Finally, this paper suggests an equivalent plain truss element model of RC structure and its crack mode. The RC structure is divided into equivalent concrete elements and steel elements. Concrete elements are equivalent plane truss element and steel elements are link elements. So by applying the uniaxial constitutive relationship of concrete to these link elements, the elastic-plastic analysis process of concrete is simplified and the calculation efficiency is improved. At the time, the process of cracks are much easier than traditional FEM. A concrete and RC simple beam and a RC shear wall structure models are analyzed with this method by ANSYS5.7. The calculation results and test results are consistent too.