Mechanical Behavior Of Steel-encased Concrete Filled FRP Tube Column Under Unidirectional Eccentric Compression

Steel-encased concrete filled FRP (fiber reinforced polymer) tube column is composed of FPR (Fiber Reinforced Polymer) tube, steel and core concrete. The excellent mechanical performance of the composite column is improved by the collaboration among the three parts. Owing to the restraint of the FRP tube, the core concrete is under three-dimensional stress condition so that the strength of the concrete is enhanced and the ductility and the plasticity are improved. The inner steel increases the bearing capacity of the column, enlarges the ductility of the column and makes seismic performance of the column better. The partial failure on the FRP tube is avoided or postponed by the core concrete in order to bring the property of the materials into full play.In the paper, experiment and finite element analysis are applied to make the research on the mechanical performance of the steel reinforced concrete filled FRP tube middle long column under the eccentric compression. The main contents in the paper include:With the slenderness ratio, eccentricity, strength of the concrete and so on as the main parameters, the experiment of7steel reinforced concrete filled FRP tube middle long columns under the eccentric compression is conducted to analyze the mechanical performance of the columns. The experiment results show that the deformation of the steel reinforced concrete filled FRP tube middle long column under the eccentric compression is obvious. The clear signs are revealed in the experiment to demonstrate the failure of the column. After the ultimate load, the bearing capacity decreases increasingly and the columns possess good ductility. The slenderness, eccentricity, and strength of the concrete have a great effect on the ultimate bearing capacity and the rigidity of the column. The restraint effect of the FRP tube on the concrete enhances with increase of the slenderness and eccentricity, but decreases with the increase of the concrete strength. The upper and lower parts of the lateral deflection curves gained in the experiment are almost symmetrical along the direction of the half height of the column and close to the half-sinusoid curves.The finite element analysis software ABAQUS is used to establish the mode of steel reinforced concrete filled FRP tube middle long column and emulate the loading process of the column. Compared with the experimental results, the validity of the finite element analysis results is demonstrated. The finite element analysis results show that the cooperative work among the FRP tube, steel and core concrete is perfect and the FRP tube make an effective restraint influence on the core concrete in the last phase of the plastic stage.The mechanical performance of the steel reinforced concrete filled FRP tube middle long column is analyzed by the finite element analysis software ABAQUS. Taking into consideration the effect of the slenderness on the columns, regression analysis is made on the finite element calculation results to receive the slenderness reduction coefficient φ1.Based on the experiment results and finite element analysis results, the calculation method of the ultimate bearing capacity of the steel reinforced concrete filled FRP tube middle long column is deduced in the paper. On the basis of the comparison between the calculation results provided by the method and the experiment results, the calculation results match with experiment results ideally so that the relative formulas can provide the references with the practice projects.