Meso-scale Simulation In Dynamic Size Effect On Compressive And Tensile Failure Of Concrete Materials

The size effect in concrete has become one of the heated issues in society recently.Great progresses have been made in static size effect of concrete,while few efforts,including generating mechanism and corresponding size effect law,have been conducted in dynamic size effect of concrete.However,due to the limitations of test equipment and techniques,it is unrealistic to explore the dynamic size effect of concrete only by physical tests,especially dynamic tests with large structural sizes under high strain rates.Furthermore,the meso-scale modelling method provide another way to study the dynamic size effect of concrete.Here in this study,taking account of the influence of concrete heterogeneities and strain rate effect in the meso-scale simulations,the concrete was regarded as a tri-phase composite material consisting of coarse aggregates,mortar matrix and the Interfacial Transition Zones(ITZs)between the former two phases.The main research contents are as follows:(1)The uniaxial compressive failure behavior of 2D concrete square specimens having different structural sizes under different strain rates were simulated by the mesoscale modelling method.The size effect on the compressive failure in concrete materials under dynamic loadings has been revealed.Moreover,the mechanism of dynamic size effect in concrete materials were discussed.(2)The dynanic size effect on the uniaxial tensile failure of 2D double notched concrete specimens were in simulations and the meso-scale simulation on the splittingtensile size effect of 3D concrete cubic specimens were conducted.The influence of strain rate effect on the size effect behavior of tensile failure and size effect behavior of splitting-tensile failure was analyzed.In addition,the mechanism of the dynamic size effect behavior on the tensile failure and splitting-tensile failure were in preliminary discussions.(3)Considering the contribution of strain rate on the dynamic size effect,based on the size effect law of Ba?ant,the semi-empirical and semi-theoretical size effect formulas of static and dynamic unity,which are suitable for describing the dynamic size effect on nominal strengths of concrete,were proposed.Finally,the rationality of the established static and dynamic unified size effect formula was verified from both views of numerical simulations and physical tests.