Research On The Axial Compression Property Of Steel Fiber Reinforced Lightweight Aggregate Concrete Filled Steel Tubes After Exposure To Fire

The lightweight aggregate concrete filled steel tubes can effectively reduce the weight of tallbuildings and the buildings with large span. For the same bearing capacity, the composite columnspresented here can save steel materials about50%compared with the steel columns. Furthermorecompared with the reinforced concrete columns, not only the template is not needed for thecomposite columns, but also the concrete can be saved by more than50%and the self-weight ofthe structure can be reduced more than50%, which will make good economic efficiency. Mixedwith a certain amount of steel fiber in light weight aggregate concrete, development of microcracks in the core concrete can be restrained and then the mechanical performance of light weightaggregate concrete filled steel tubes can be improved.The shale ceramsite is used as the main raw materials of the core concrete. Three of variablefire temperatures, three of steel ratio and four of steel fiber volumn are considered for theexperiment. Experimental investigation of24of the axially loaded steel fiber reinforcedlightweight aggregate concrete filled steel tubes (noted as SFCFST) after exposure to fire and12ofones not subjected to fire load were conducted here. In this paper, effect of the factors such as steelfiber volumn and steel ratio on the ultimate bearing capacity of the SFCFST after exposure to firewas experimentally investigated for the fire conditions with fire temperature of700℃and900℃，which was compared with the results of SFCFST at room temperature. Based on the correspondingexperiment, the experimental phenomenon and the failure pattern of the SFCFST after exposure tothe fire and ones not subjected to fire load were observed and analyzed. According to thecorresponding load-strain curves and load-displacement curves of the short columns for thedifferent steel fiber volumn and steel ratio，the post-fire residual bearing capacity of the columnsafter exposure to fire and the bearing capacity of the columns not subjected to fire load were allanalyzed and compared.The experimental results show that the axial compression damage form of SFCFST afterexposure to fire is in basic agreement with that of the columns not subjected to fire load, whichpresent the form of shear failure and local protrusion. The axial compression bearing capacity ofthe columns after exposure to fire and that not subjected to fire load can be improved by proper incorporation of steel fiber into the core concrete, which show that the volumn of0.5%is the bestamong four steel fiber volumns of0,0.5%,1%and1.5%. As the steel fiber volumn is more than0.5%, the ultimate bearing capacity of the short columns reduced slightly with increase of steelfiber volumns. Effect of steel fiber on the mechanical performance of SFCFST decreased withincrease of the steel ratio. The thermal response of core concrete is behind that of the steel tubeunder fire, and the results of numerical simulation are basically consistent with the results ofexperiment. According to the test results, correction coefficient of axial compression bearingcapacity of SFCFST was put forward considering effect of steel ratio based on the Specification fordesign of steel pipe concrete. The revised formula can be used for calculation of axial compressivebearing capacity of SFCFST not subjected to fire load, and the result obtained from the formulapresented here concides well with the corresponding experimental results.