Experimental Study On Dynamic Mechanical Properties Of Concrete Under Different Strain Rates

In recent years,emergencies such as terrorist attacks,natural disasters and man-made accidents happened frequently,which lead to shock and impact load on engineering structures.The safety of the engineering structure has been threatened seriously.The reinforced concrete structure is widely used in engineering,and the research on the dynamic mechanical properties of concrete has attracted the attention of scholars both at home and abroad.At present,there are many theoretical and experimental studies on the dynamic mechanical properties of concrete,but there are few studies in the range of middle strain rate and high-strength concrete.In this paper,dynamic mechanical properties of C30,C40,C50 and C60 concrete were investigated by using the Split Hopkinson Pressure Bar(SHPB)and the drop hammer impact test system.In addition,the finite element(FE)simulation of impact test results with drop hammer were carried out by FE program LS-DYNA.The main contents of this paper are as follows:(1)Dynamic mechanical properties of four strength grades of concretes in which the magnitude of strain rate is 102/s were examined by using SHPB.The waveforms,stress-time curves,strain-time curves and strain rate-time curves were obtained.Furthermore,three-wave mutual-checking method was utilized to verify the typical waveforms obtained during the experiments.The effects of strain rate on dynamic stress-strain curves of concretes,ultimate strain and the dynamic increase factor(DIF)were analyzed,and the dynamic mechanical properties of concretes with different strengths were compared.(2)To achieve a constant rate of impact loading,an improved drop hammer impact test device was adopted while rubber was used as wave shaper.And the influence of the inertia force on the measurement of the upper force sensor of the specimen is discussed.The impact tests in the strain rate range of 10-1/s?100/s of four strength grades of concretes were carried.The stress-time curves and strain-time curves at different impact rates were obtained,and the influences of strain rate on dynamic stress-strain curves,ultimate strains,energy absorption and dynamic compressive strengths were studied.The strain rate effect of concretes with different strengths was compared.(3)The literatures of SHPB tests and drop hammer impact tests were statistically analyzed,and the influences of concrete strength and size of specimen on DIF were reviewed.The empirical formulas of the dynamic increase factor of concrete under the impact load were summarized,and their rationality in describing the relationship between DIF and strain rate were discussed.(4)The drop hammer impact tests of different strengths concretes were simulated by finite element software LS-DYNA.The failure and cracking process of the concrete specimens were analyzed,and the numerical simulation results and the test results were compared.