Numerical Study Of Influencing Factors On The Properties Of Concrete Material Under Dynamic Compression With Confining Pressure

Because of the excellent mechanical properties,concrete has been widely used in various types of construction projects.In practical applications,such as the underground structure subjected to impact loads,the stress state of concrete is very complex.Therefore,it is essential to understand the dynamic mechanical properties of concrete under complex stress state.At present,the dynamic compressive performance of concrete materials with confining pressure is mainly obtained by the active confining pressure split Hopkinson pressure bar(SHPB)test.It is now commonly agreed that the lateral inertia confinement,end-friction confinement and aggregates have obvious influences on the compressive properties of concrete material in impact tests.The results that directly measured in the test may not reflect the real material properties of the material.Although the active confining pressure SHPB test has been widely used in measuring the dynamic behavior of concrete materials with confining pressure,the discussion on the problems that existing in the experiment is not enough.In this paper,the LS-DYNA finite element software is used to simulate the active confining pressure SHPB test.The effects of lateral inertia confinement,end friction and aggregates on the test results has been discussed.The detailed work is as follows.(1)The finite element model of active confining pressure SHPB test was established and the numerical simulation of the active confining pressure SHPB test was completed.Four kinds of confining pressure are adopted in the simulation,and the influence of lateral inertia confinement on the test results in different confining pressure and strain rate are discussed.At the same time,in order to modify the influence of lateral inertia confinement,a correction formula is given based on the simulation results.(2)Different kind of friction coefficient,confining pressure and strain rates are adopted in the simulation to figure out the influence of end friction to the test.According to the simulation results,the influence of end friction with different friction conditions,confining pressures and strain rates are discussed.A correction formula is given to modify the influence of end friction to the test results.(3)In order to analyze the influence of aggregates on the dynamic behavior of concrete,a mesoscopic model of concrete which containing aggregate is established.The differences of the dynamic strength between the concrete specimen with and without aggregates are compared in different confining pressure.At the same time,the differences between the failure modes and crack development process of the concrete specimen in different confining pressure and strain rate are analyzed.In order to reflect the influence of aggregates to the dynamic strength of concrete,a formula of the contribution of aggregates to the dynamic strength of concrete in different strain rates and confining pressure is given.