Study On Lateral Reinforcement And Axial Compressive Behavior Of Reinforced Concrete Filled Steel Tubular Columns

With the acceleration of urban development,the demand for high-capacity and high-stability buildings is increasing.Coupled with the frequent occurrence of natural disasters such as earthquakes in recent years,There is a necessity for exploration and research on structures with excellent mechanical behaviours.According to the existing research results,R-CFST shows good mechanical properties,Therefore,there is practical significances to conduct in-depth research.According to the current research situation,the research on the performance of the stirrups in R-CFST is relatively rare,and the research on its influence mechanism has great effects on improving and optimizing the design,construction and economic benefits in engineering practice.Therefore,this study mainly focuses on the experimental study,nonlinear F.E.simulation study and calculation formula of the axial bearing capacity of the reinforced concrete-filled steel tube R-CFST with the stirrups as the research object.In the experimental study,the main parameters are the spacing and pattern of the hoop.The transverse reinforcements were configured in spiral and flat hoop patterns,in which flat hoops with three different spacing values.The eight R-CFSTs specimens were subdivided into four groups,along with three CFST specimens and three plain concrete specimens.By comprehensive analysis of the test results,it was found that the before-ultimate load transfer performance and ultimate load-bearing capacity of R-CFST stub columns subjected to an axial load are not relevant to neither the patterns of the transverse reinforcements nor spacing of the of flat hoops,and the influence effect can be neglected when calculating the bearing capacity of the axial compression;differences in the spacing of the flat hoops will not cause significant changes on the mechanical properties of the member,so in the practical engineering,a larger stirrup spacing can be used to improve work efficiency and economic efficiency;in the case of the same stirrup spacing,compared to flat hoops,spiral hoops will improve the ductility and post-ultimate loading performance further,and thus,the spiral hoop is recommended when the ductility or seismic performance is the main concern.Based on the experimental results,a numerical analysis model was established,and the nonlinear numerical analysis was carried out.The reliable test specimens model were proposed and further verified.The accuracy of the test results and the reliability of the numerical simulation model were verified based on the test results.Finally,six groups of R-CFST numerical analysis models with different concrete stength are established for analysis using the established numerical analysis method.Each set of models includes six steel pipe wall thicknesses and 3 longitudinal ratio,a total of 108.Through the results,it is found that the "combined theory of concrete filled steel tube" also applies to R-CFST.Therefor,the calculation method of R-CFST axial compression bearing capacity is studied according to the CFST research method,and the corresponding bearing capacity calculation formula is proposed,compared and verified.The results show that this formula can be used in engineering design.