Study Of Mechanical Performance Of Axially Loaded Self-stressing Lightweight Aggregate Concrete Filled Steel Short Tubes After Fire

The self-stressing lightweight aggregate concrete filled steel tubes (SLCFST) is one of newlydeveloped concrete filled steel tubes (CFST), it has the advantage that the lightweight aggregateconcrete filled steel tubes and the self-stressing concrete filled steel tubes have. Compared with theordinary concrete filled steel tubes, the seismic performance of SLCFST is better because of thereduced self-weight of the structure. The problem of decline of the restraining action of steel tubeto core concrete, which is caused by the factors of inadequate vibration of concrete during pouring,lower stiffness of the lightweight concrete, shrinkage and creep of concrete, is solved by the initialself-stress, and the fire-resistance performance of steel-concrete composite structure is better. Atpresent, the mechanical property of ordinary concrete filled steel tubes after fire has been studiedby many researchers, but the research on lightweight aggregate concrete filled steel tube is less, andstudy of the self-stressing lightweight aggregate concrete filled steel tubes has not been found inthe previous references. So, the research on mechanical property of SLCFST at room temperatureand after fire is important and valuable for theoretical and practical application.The expansive property of nine self-stressing lightweight aggregate concrete filled steel tubeswas experimentally investigated first, and the parameters such as steel ratio, mixing amount ofexpansive agent were discussed. The temperature response of SLCFST in fire was measured, andthe temperature field is simulated and analyzed by FEM software Marc. The mechanical behaviorof eighteen axially loaded SLCFST after exposure to fire and nine ones not subjected to fire loadwas investigated and the parameters such as steel ratio, mixing amount of expansive agent andtemperature under fire were considered. The effect of each parameter on axial compressionbearing capacity and deformation of SLCFST at room temperature and after fire has been analyzed,and comparative analysis of the axial compression mechanical behavior of the short columns indifferent conditions was conducted.The research results show that the inflatable restraint of steel tube to core concrete increasedwith steel ratio, and the value of self-stress is linearly proportional to the mixing amount ofexpansive agent. The temperature response of core concrete is behind that of the steel tube underfire, and the results of numerical simulation are basically consistent with the results of test. It isseen that the self-stress can enhance the axial compression bearing capacity of the concrete filled steel tube not subjected to fire load and the post-fire bearing capacity and stiffness of thelightweight aggregate concrete filled steel tubes after exposure to fire is improved by the initialself-stress, but the effect decreased with the fire temperature rise. It is also found that The self-stress has more significant influence on mechanical property of the short columns with lower steelratio. The effect of fire temperature on the residual bearing capacity of the short columns presentedhere was discussed based on the experimental results obtained here, and the method of calculationof axial compressive bearing capacity of SLCFST was put forward based on the design guidelineof ordinary concrete filled steel tubes, in which the effect of self-stress is especially considered.