Dynamic Behavior Of Concrete-filled Steel Tube (CFT) In Fire(High Temperature) And After Exposure To High Temperature (Fire) Under Impact Load

In recent years, frequent building fires and terrorist attacks have caused huge losses because of building collapse after (in) the fire. The research results on behaviors of undergoing the static load and under impact load at room temperature show that concrete filled steel tube (CFT) not only has good fire resistance and post-fire mechanical behaviors, but also has good impact resistance at room temperature. This means CFT in fire exposure (under high temperature) may have good impact-resistant and anti-collapse capacity, and is suitable for a good structure of anti-fire collapse. In this paper, drop test machine was used to study the impact-resistant behaviors of CFT under and after exposure to fire or under high temperature, and theoretical model was built to analyze the experimental results using well-known finite element program ABAQUS/Explicit, The beneficial conclusions were drawn from the tests and theoretical analysis and can provide references for the structure anti-collapse design. The main jobs have been done as follows:(1) A controllable new hybrid heating method was developed, namely heating using electric furnace and gas fire synchronously. Temperature debugging was carried out following ISO-834 standard fire curve and actual fire curve which can provide a basis method for fire test.(2) Drop impact tests on concrete-filled steel tube (CFT) short columns after high temperature were carried out. Test parameters including the high-temperature, impact velocity, impact energy, steel ratio and axial load level were considered and the influence of the axial load level (n) on the ultimate impact force and residual deformation was discussed especially.(3) Drop impact tests on concrete-filled steel tube (CFT) short columns under ISO-834 standard fire curve were carried out at the first time. Test parameters including fire duration time, impact velocity, impact energy, steel ratio, slenderness ratio were considered and the influence of fire duration time to the maximum impact force and residual deformation was discussed especially.(4) Drop impact tests on concrete filled steel tube beams under high temperature were carried out at the first time. Test parameters include impact velocity, impact energy and fire duration time.(5) A finite element model using ABAQUS/Explicit program was developed to analyze behaviors of CFT members under and after fire. Numerical simulation about the impact tests of CFTs were developed. The results compared fairly well with the experimental results, and a simple impact-resistant design method was suggested in this paper.