Research On Compressive Behavior Of Concrete-filled Round-ended Steel Tubular Stub Columns With Binding Bars

As is known,concrete-filled steel tube has many advantages,such as excellent mechanical properties,diverse structure and functions,convenient construction and economical performance.Therefore,it has been extensively studied and widely applied as well as continuously innovating.Concrete-filled round-ended steel tube(R-CFST)is a new type of cross section which has strong bearing capacity,bending performance and conforms to architectural aesthetics and anticollision design,so it is widely used in Bridge Engineering.But at present,the research on the theory and design of R-CFST is very short,which hinders the wide application of R-CFST.In this paper,the axial compression behavior of R-CFST is studied.The main research contents,methods and conclusions are as follows:(1)Finite-element simulation of R-CFST is set meticulously.5 expressions of Ding Faxing,Hongnestad and Han Linhai(round,rectangular)and Guo Zhenhai are compared.Compared with the 5 calculation results and test results,it shows that the expression of Guo Zhenhai is most suitable for R-CFST.(2)Axial compression performance of R-CFST is analyzed.The result shows that: the restraining effect of steel tube on the core concrete is stronger in the arc section,and is weaker in the straight section.The core concrete in the arc section is separate from steel tube.The restraining effect,increase coefficient of bearing capacity and ductility is enhanced with the increase of steel strength or steel tube thickness and the decrease of concrete strength or ratio of height to width.When H/B is small,the restraining effect of R-CFST is similar to that of circular concrete-filled steel tube.When H/B is large,the restraining effect of R-CFST is similar to that of rectangular concrete-filled steel tube.(3)By analyzing the restraint mechanism of R-CFST with binding bars,a strong / weak restraint area of concrete section is established,and the stress state is simplified.The steel tube is regarded as the plane stress state under cyclic tension and radial compression.The concrete section of R-CFST is divided into one rectangular section and two semicircle section.On the basis of reasonable simplification and section division,the constitutive relationship of R-CFST with binding bars is deduced.The reasonableness of the constitutive relation is verified by comparison with the previous experimental results.(4)The axial compression performance of R-CFST with binding bars is analyzed.The results show that when the load reaches the ultimate bearing capacity of the axial compression,the average stress value of all the binding bars is about 350 MPa,which is in plastic state,indicating that the binding bars have been fully developed and finally yielded during the whole loading process.The axial compressive peak strain of RCFST with binding bars is about 0.06,which is 1 times higher than that of the common component.The contact stress at the flat section of R-CFST with binding bars can reach 11.256 MPa,the setting of the binding bars can effectively make up the shortcoming of the weak constraint effect in the flat section.With the increase of the diameter of binding bars,the decrease of the axial distance between binding bars and the increase of the number of binding bars,the ultimate bearing capacity,the residual bearing capacity and ductility of the axial compression are all improved.With the increase of H/B,the increase coefficient and the bearing capacity are decreased.(5)On the basis of the numerical calculation results and the analysis of the axial compression short column,the general formula of R-CFST under axial compression is obtained.The rationality and correctness of the formula are verified by comparison with the results of numerical calculation and the calculation results of common standard formulas.