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

With the rapid development of the country in various industries,building forms tend to be high-rise buildings and long-span bridge structures due to human needs.Concrete-filled steel tube has always been the most widely used structure type due to its own characteristics,and at the same time,with the use of high-strength materials,it can further enhance its mechanical properties.However,there are still problems of self-weight and low space utilization in actual projects.In order to improve such problems,the research group proposed to configure a new type of steel-concrete composite structure with I-shaped CFRP profiles in the traditional high strength concrete-filled high strength square steel tube columns.The composite structure combines the advantages of the three materials to strengthen its mechanical properties.In this paper,through the combination of finite element simulation and experimental analysis,the mechanical properties of high-strength square steel tube high-strength concrete middle-long columns with built-in I-shaped CFRP profiles under axial load are comprehensively and systematically analyzed.This paper has carried out the following research work: experimental research on high strength concrete-filled high strength square steel tube middle-long columns with inner I-shaped CFRP under axial load,recording the changes of the specimens during the test,and comparing and analyzing the failure of various internal components after the test failure Modal,explore the influence of slenderness ratio and steel yield strength on the ultimate bearing capacity and mechanical properties of members;compare the finite element analysis model,and verify the load-deflection curve and limit of the composite column under the axial compression state obtained by the numerical simulation with the test results Bearing capacity,determine its accuracy.Subsequently,a large number of finite element models were established to analyze the full-process curve of the composite column,to study the stress change law of the material,the failure mode,the load condition of the different height sections and the interaction between the components;the analysis of parameter changes The influence trend of bearing capacity,stiffness and ductility,the mechanical performance of composite members under different parameter changes are summarized;finally,the data obtained by finite element simulation is sorted,and the composite medium-long column suitable for the section type of this article is regressed and calculated The formula for calculating the stable bearing capacity is verified by the variable parameter model and test results to verify the applicability of the formula to determine its accuracy.The research results show that the load-medium section lateral deflection curve of high strength concrete-filled high strength square steel tube middle-long columns with inner I-shaped CFRP under axial load can be divided into 5 characteristic points and 4 characteristic stages:elastic stage,Elastic-plastic stage,plastic strengthening stage and descending stage;CFRP profiles and members do not reach each other’s ultimate bearing capacity state at the same time,and confine the concrete together with high-strength steel pipes to increase its compressive strength,thereby improving the overall bearing capacity of the members;steel to concrete The restraining effect of CFRP is mainly reflected in the compression side bend area,followed by the tension side bend area,and the flat plate area has basically no restraint effect;I-shaped CFRP profiles are used in low slenderness,low strength concrete and high yield strength steel components Play a more significant role.Finally,based on the unified theory of concrete-filled steel tube,the calculation formula for the stable bearing capacity of the composite column under axial load is derived,and the applicability and accuracy of the formula are verified.