Experimental And Numerical Study On SHPB Impact Behaviors Of Concrete-filled Steel Tube At Elevated Temperatures

Since the event of 911, dynamic behavior of building structure has caught the attention of researchers. However, attack of terrorism, such as car bomb, and explosion of chemical factory may introduce a large quantity of heat and elevated temperature to heat the structure. Simultaneously, fire high frequently happened in buildings may also lead to gas explosion. Temperature and dynamic loading may both impact the building structure under all these situation, leading to local destroy, even whole collapse. There has been little research on the impact (collapse) behavior of structures under fire (high temperature) at present. The split Hopkinson pressure bar (SHPB) and a purpose-built electrical furnace were used to investigate the dynamic behavior of concrete-filled steel tube (CFT) under elevated temperatures in this paper, and numerical model was also built to simulate the experiment using ABAQUS. The main work as follows:(1) Methods study of SHPB impact test under high temperature. The specimen heated by the schedule determined by numerical simulation can high reach an uniform temperature field.(2) Experimental research on the dynamic behavior of CFT under elevated temperatures. Strain versus time, stress versus time, and stress versus strain curves were gained, and effects of temperature, impact velocity (strain rate), steel radio and slenderness radio on the dynamic behavior of CFT under high temperature were analyzed.(3) The dynamic behavior of concrete under high temperature was experimental studied. Strain versus time, stress versus time, and stress versus strain curves were obtained, and effects of temperature and impact velocity (strain rate) on the dynamic behavior of concrete under high temperature were analyzed. Based on the dynamic mode of concrete suggested by CEB, a relationship function between DIF (dynamic increase factor) and temperature and strain rate was got for the hot concrete.(4) The SHPB impact tests of CFT under high temperature were numerically simulated by ABAQUS, whose results tallied with the test results. Based on this numerical model, the effects of several factors such as steel radio, concrete and steel strength on the dynamic behavior of CFT were analized. Also, the constraint effect of CFT at peak stress under dynamic loading was studied. An empirical formula was built to estimate the dynamic strength of CFT under high temperature, which was highly supported by the numerical results.