FEM. Program Design For Dynamic Behavior Of Concrete

It is unavoidable to encounter dynamic loads during the use of concrete structure, such as seism, tsunami, impact, blast and etc. The static mechanical behaviors of concrete are usually adopted in structure dynamic analysis. However, the results of many researches indicate that concrete is one of the rate-dependent materials and its dynamic mechanical behavior is different far from the static one. In dynamic analysis, it can't be ignored the effect of dynamic behavior of concrete on the dynamic response of structure. But it is very difficult to carry out the structural dynamic calculation with the dynamic constitutive law of concrete defined newly by ourselves using the commercial FEM. software. Therefore, in this paper a program named RDDP (rate-dependent dynamic program) is formulated to solve the dynamic analysis problem.As a subtopic of project "Research of dynamic characteristics and damage mechanism of concrete", which is funded by academician subject development fund of HoHai University, the main objective of this paper is to write a FEM. program to be able to do the dynamic numerical calculation with consideration of the dynamic mechanical characteristic of concrete. As the fundamental work of numerical simulation, the program can use the ANSYS software to do the preprocessor and postprocessor by data exchange. Firstly, a strain rate factor is introduced to correct the static uniaxial constitutive law of concrete and establish the equivalent uniaxial dynamic constitutive law based on experiment data of dynamic mechanical characteristics of concrete: In order to use the model in numerical calculation, this paper deduces the iteration format for solving the dynamic equilibrium equation considering the hypoelastic material model. Then, the flowchart and framework of the program written with FORTRAN language are listed in detail. Every module of the program is verified by calculation with many material models under different cases. Finally, an experiment of third point flexural concrete beam under static loads and dynamic loads is simulated by the program, and then the calculation results and experiment results are compared and analyzed. The argument between them is satisfactory.The program has some special functions which provides good foundation for further study. 1) The program can carry out the three dimensional structural dynamic calculation considering the rate-dependent behavior of concrete. 2) The program can make full use of the ANSYS software to do the preprocessor and postprocessor of FEM through data exchange. 3) The problems of nonlinear static and dynamic analysis with different materials and loading modes can be solved in one program, because many key options are set to solve different problems. 4) The program provides several material models to be chosen and the models can be modified easily if it is necessary.By the analysis and calculation, two conclusions can be drawn as follows. 1) The rate-dependent constitutive law and failure criterion of concrete formulated in this paper can describe the dynamic characteristics of concrete that the strength of concrete increases with the increase of the strain rate.2) According to the calculation results of third point flexural concrete beam, we can find that the dynamic flexural tension strength of concrete increases about 8% of static strength as the strain rate increases ten times.