| There are relatively few studies on the tensile performance of concrete filled steel tubes at home and abroad,and most of the relevant researches focus on specimens with circular cross-sections.The studies on specimens with opposite cross-sections are more common in welded square steel tubes.Performance research is still rare.In addition,the existing formula for the axial tensile bearing capacity of concrete-filled steel tube is not clear to a certain extent,and the application scope of the formula needs to be improved.Therefore,this paper studies the mechanical properties of cold-formed concrete-filled square steel tubes under axial tension and partial tension from two aspects of experiment and finite element simulation.The specific work and main conclusions are as follows:(1)With concrete strength,cross-section width-thickness ratio and whether filled with concrete as parameters,six cold-formed concrete-filled square steel tube axial tensile performance experimental studies were carried out,and the experimental phenomena and experimental data were analyzed.The results show that with the increase of the width-to-thickness ratio,the fracture strain of the specimen shows a decreasing trend;the failure position of the specimen is concentrated in the middle and 1/3 of the height of the specimen from the loading end,and most of the section has oblique cracks along the 45° direction.When the longitudinal micro-strain of the cross-section measuring point in the specimen is about 150,the core concrete cracks and the stiffness of the specimen is reduced;in the range of the width-thickness ratio of 31.11-36.36,the filling of concrete affects the axis of the cold-formed square steel tube The increase in tensile bearing capacity is about 5%;the calculation results of axial tensile bearing capacity of American standard AISC,British standard AS5400,European standard EC4 and China’s technical code for concrete-filled steel tube structures GB50936 are more conservative than the test results in this paper.(2)The finite element software ABAQUS was used to establish a model of the axial tension test piece,which was compared with the test results to verify the validity of the model,and the working mechanism of the test piece was analyzed in conjunction with the test part.On this basis,the parameter expansion was carried out,and the calculation formula of the axial tension bearing capacity of cold-formed concrete filled square steel tube was fitted.The results show that the strength of concrete has little effect on the bearing capacity,and the aspect ratio and the strength of steel have a significant influence on the bearing capacity of the specimen;in the range of the aspect ratio of 15-240,the bearing capacity of the specimen filled with concrete is improved The range is 3.03%-30.75%.(3)With the main parameters of material strength,width-to-thickness ratio,slenderness ratio and eccentricity,a numerical simulation of the eccentric tensile performance of cold-formed concrete-filled square steel tubes was carried out.The initial flexural rigidity and the flexural rigidity of the specimen during use were calculated.The value is in good agreement with the calculated value;the calculation method of the flexural bearing capacity in the Japanese code AIJ2008,the British BS5400,the Chinese steel tube concrete structure technical code GB50936 and the document [1] are introduced,and the bearing capacity calculated by the code and the finite element simulation result are introduced.A comparison is made and it is found that the calculated values of the first three procedures are relatively conservative.The calculated results in the literature [1] differ by about 7% from the finite element simulation results,which is the closest.The related equations for the bearing capacity of the cold-formed concrete-filled square steel tube specimens in eccentric tension are sorted out,and this equation is in good agreement with the simulation results of the eccentric tension specimens in the article. |
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