Research On Mechanical Behavior Of High Strength Concrete-filled High Strength Square Steel Tube Stub Columns With Inner I-shaped CFRP Under Axial Load

Concrete-filled steel tube composite columns(CFST)with the advantages of high bearing capacity,good durability and convenient construction has been used in practical project.Many scholars around world made many thorough-going analyses of CFST mechanical properties.In recent years,high-strength materials,FRP materials,et al,have been rapidly developed,which were applied in civil engineering,especially in new composite structures.Combining the advantages of high-strength material and FRP material,I-shaped CFRP and high-strength concrete are applied to concrete filled steel tube composite columns,a new type of composite structure column-high strength concrete-filled high strength square steel tube columns with inner I-shaped CFRP,has been proposed.The new composite columns have the advantages ofhighbearing capacity and good ductility.In this paper,a comprehensive analysis was presented on the mechanical behavior of high strength concrete-filled high strength square steel tube columns with I-shaped CFRP by the test,finite element analysis methods and theoretical research.Through the experimental study on the mechanical behavior of 8 high strength concrete-filled high strength square steel tube stub columns with I-shaped CFRP under axial load,the failure modes,ultimate bearing capacity,steel tube load-strain curves and the I-shaped CFRP load-strain curves of specimens were obtained.Base on experimental research,finite element analysis software ABAQUS was used to simulate the high strength concrete-filled high strength square steel tube stub columns with I-shaped CFRP under axial load.Combining the test and finite element simulation results,the correctness of the finite element model was proved.Based on the experimental and finite element simulation results,the stress distribution of I-shaped CFRP profiles,core concrete and square steel tubes,the variation of load sharing and contact stress in the whole process of loading were studied.The effect of different parameters on the mechanical behavior of specimens was analyzed.Based on the experimental and finite element results,the bearing capacity calculation method of high strength concrete-filled high strength square steel tube stub columns with I-shaped CFRP under axial load was obtained through data fitting.The results show that the whole process of axial compression short columns of is divided into five stages:elastic stage,elastic-plastic stage,plastic strengthening stage,decline stage and stationary stages;the I-shaped CFRP profiles bears a larger load at the middle section area,while the concrete bears larger load at the end-section area;the strength of core concrete increases due to the concrete is restrained by I-shaped CFRP and high-strength square steel tube;three parametric studies have been conducted to evaluate the effects of ultimate bearing capacity and initial stiffness of models,the better confinement effect with a larger ultimate bearing capacity is clearly illustrated by higher concrete strength,steel ratio and steel yield strength,the initial stiffness of models increase with steel ratio and concrete strength,but yield strength of steel,ductility coefficient decreases with the increase on steel ratio,concrete strength and yield strength of steel;the computing methodof the bearing capacity deduced by the test and finite element simulation results are in good agreement with the experimental values and results of finite element method.