Concrete Dynamic Constitutive Model Based On Damage And FEM Analysis

Based on the realization that concrete is a kind of heterogeneous material with microcrack, and concrete structural system becomes more and more complicate and is usually subjected to dynamic loads such as earthquake, impact and blast, the research on concrete mechanical behaviors progresses at a rapid rate, whose direction is from static to dynamic state, from uniaxial to triaxial stress state, and that the effect of damage evolution on concrete is considered. At the same time, the research on constitutive theory of concrete, as a common building material, is for engineering application in the final analysis. So this paper aims at presenting dynamic constitutive model of concrete based on damage which can be accepted by engineers and convenient for engineering designs.According to synthesizing and analyzing the present research status of dynamic constitutive model, damage theory, static and dynamic failure criterion of concrete, this paper presents dynamic constitutive model of concrete in uniaxial tension and compression. And by defining tension stress index, non-linearity index and equivalent uniaxial elastic modulus, the uniaxial constitutive models are extended to triaxial stress state. And then, the material parameters of these models are fitted by BP artificial neural network (BP NN), and the models are verified further. At last, this paper makes numerical calculation and analysis with spatial rate dependent dynamic FEM program programmed by this subject (RDDP).By superimposing strain rate strengthening factor and damage weakening factor upon static constitutive model of concrete, uniaxial dynamic constitutive models based on damage are built, which are clear in conception. And the results of parameters fitting of the constitutive models by BP NN show that theoretic models anastomose with experimental data well. This paper identifies two kinks of basic damage forms with tensile stress index: tensile failure controlled by tension stress and crush failure controlled by compression stress; and modifies concrete behaviors such as strength, strain at critical stress with non-linearity index; and gets equivalent uniaxial elastic modulus by means of weighted average of elastic modules modified by non-linearity index in three principal stress directions. Accordingly the relationships of stress-strain in uniaxial tension and compression are extended to all kinds of spatial stress states such as tension-tension-tension, tension-tension-compression, tension-compression-compression, compression-compression-compression etc, and it is realized well that unixial constitutive model is extended to triaxial constitutive model. In dynamic loads, the damage evolution law of concrete in compression differs from in tension; however, Loland model, which is based on research on damage evolution law in tension, can also simulate the damage evolution law well by introducing crack closing factor. The failure criterion of concrete in dynamic loads differs from in static loads; however, the dynamic failure criterion can bebuilt by considering the effect of dynamic behaviors based on static failure model, which offers a feasible way for research on dynamic failure criterion of concrete at the present of lacking comprehensive dynamic experimental data. The results of numeric calculation with RDDP validates correctness of the method deduced from unixial model to triaxial model to some degree, and the successful realization of numeric analysis lays a foundation for dynamic FEM calculation of spatial structures with this model.