Research On Ultimate Load-Carrying Capacity Calculation Methods Of Composite Column With CFST Stiff Skeleton

Steel-concrete composite structure has been widely used as building columns. As for bridge engineering, the construction method that using the concrete-filled steel tubular (CFST) members as stiff skeleton is often be applied for concrete arch bridges, but the carrying capability of the stiff skeleton is ignored. In order to meet the requirements of larger span and easy construction, a new type of composite concrete arch is presented, in which the CFST members are used as stiff skeleton in arch rib and the trussed steel tubes are utilized as connections, the carrying capability of the stiffen skeleton is also considered. As arch carries the load using compression, the new composite arch can be simplified as composite column with CFST stiff skeleton. Existing researches on the new composite columns all define the peak load of load-displacement curve as the ultimate load, which is not reasonable for the application of bridge engineering. Therefore, focusing on the application of bridge engineering, marking the outsourcing concrete flaking as symbol, experimental researches and FEM analysis on columns with CFST stiff skeleton are carried out in this paper. The main works of this paper include the following:(1) The axial-compression experiments with the main parameter of area ratio are carried out. The result indicates that the whole loading process can be defined as the elastic、elastic-plastic and plastic stage. The mechanical performance and failure modes of composite column vary with different area ratio. The load-carrying capacity of marking the outsourcing concrete flaking as symbol is not necessarily the same with the peak load.(2) Experimental comparison results show that the area ratio not only influences the value of the first-crack load, the flaking load and the peak load of the composite column, but also the ratio of others to the ultimate load. With the increase of area ratio, the first-crack and the flaking load increase firstly and then decrease, as well as the ratio of the first-crack-load to the peak load, while the ratio of flaking load to the peak load decrease gradually. The trend is the same for the specimens with different the amount of longitudinal reinforcement or eccentricity ratio.(3) Finite element models based on the ABAQUS software, verified by the test result, is used for extending parameter analysis. The numerical results show that effect of area ratio on the ultimate load of composite columns with CFST stiff skeleton is similar to the test result, and the mainly influences including area ratio, the amount of longitudinal reinforcement and strength of steel and concrete.(4) Based on the test results and finite element analysis, combining with the existing calculation methods, a formula based on the area ratio of ultimate load-carrying capacity for composite columns with CFST stiffened skeleton is proposed. The accuracy analysis of the method shows it is available for engineering application with error in less than 10%.