| Steel fiber reinforced concrete (SFRC) is concrete made of hydraulic cements containing fine aggregate, coarse aggregate, and with randomly oriented steel fibers. The constitutive relationship of SFRC under intermediate strain rate is studied from different analysis of theory and experiment in mis dissertation. The main work of this dissertation is summarized as following:1. In chapter 1, a comprehensive survey of constitutive models of SFRC is presented. Some of the most important aspects of the research on dynamic performances of SFRC are reviewed. Some main issues of which remain to be solved are outlined. The engineering background about the thesis selecting is introduced.2. In chapter 2, the basic information of a self-developed SFRC dynamic test system matching with Instron 1342 materials testing machine is given. The scheme of experiment, the specimen fabricating, the processes of both loading and measuring are introduced in detail. The complete process of SFRC under tension (four-point flexure, cleavage ) with different strain rate from 1.0x 10-4 s-1 to 1.0x10-1s-1 has been investigated. By this system, the complete stress strain curve for SFRC under intermediate strain rate is obtained.3. In chapter 3 and chapter 4, the experimental results of SFRC under intermediate strain rate are analyzed. The results indicate that the stress strain curves in the process with different strain rate are somewhat similar, with the peak stress and peak strain corresponding to peak stress and elastic modulus (secant modulus) increasing in different degree when the strain rate increases. While the strain rate increases from 1.38 X 10-4s-1 to 0.532 X 10-1s-1, the tensile strength of SFRC increases around 30%, the peak strain of under peak stress increases 10%, the dynamic tensile elastic modulus increases 20%. Under intermediate strain rate (e=1.0x10-4s-1 ~1.0x10-1s-1), while the contents of steel fiber increases from 0% to 4%, the tensile strength of SFRC increases around 130%.4. In chapter 5, the constitution theory of SFRC under intermediate strain rate is studied in detail. Based on energy theory, the general form of nonlinear hyper-elastic constitution equations for cement-matrix materials is got. Based on the comprehensive analysis of the experimental data, some statistics curves ofmathematical statistics method are used to describe the stress-strain relationship of SFRC under intermediate strain rate. The basic theory of the new method is introduced. After combining mathematical statistics method with the nonlinear hyper-elastic constitution model for SFRC, the complete stress-strain curve of SFRC may be prognosticated by using a part of the data of stress- strain. At the same time, based on the theory of elastic-plasticity mechanics, the general form of a rate-dependent's elastic- plasticity constitution equations for SFRC is got. An analytical method has been used to determine the effective elastic modulus of SFRC with randomly distributed steel fibers. The influence of boundary effect and gravitation effect of randomly distributed steel fibers and concrete matrix porosity are taken into account in this method. Based on a series of theoretical and experimental analysis, a four-phase composite model has been proposed to calculate the effective elastic modulus of SFRC. By this approach, some simple, explicit formulae are derived for estimating the effective elastic modulus of SFRC. Based on the analytical results, the rate-dependent's elastic- plasticity constitution model for SFRC is improved. And finally, the rate- dependent's elastic-plasticity constitution model and nonlinear hyper-elastic constitution equations for SFRC are validated by experimental data.5. In chapter 6, for a better understanding of the fracture behavior of SFRC composite materials under loading (including dynamic loading), the theoretical analysis method has been used to discuss the reinforcing mechanism and the mechanical behavior of crack in micro-crack zone of SFRC. Based on a series of theoretical anal...
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