Research On Mechanical Properties Of Circular Concrete-filled Steel Columns Confined By Hoops Based On Numerical Simulation

In recent years, concrete filled steel tube have been widely used in column construction of tall buildings, due to its superior strength and ductility performance contributed by the composite action. Moreover, the steel tube can serve as formwork for concreting, which results in saving the construction cost and shortening the construction cycle time. Also, by confining the concrete with the steel tube, local buckling of steel tube can be prevented or at least delayed by the core concrete and the core concrete can be confined effectively, hence, the ultimate supporting capacity of CFST have improved. However, this cannot be fully developed at early elastic stage as steel dilates more than concrete and thereby causing imperfect interface bonding, which reduces the elastic strength and stiffness. This situation even worse for CFST columns filled with HSC and UHSC, which would result in tube buckling in the early elastic that reduces the elastic strength.To resolve the problem, confinement in the form of rings is proposed by scholars from HKU to restrict the elastic lateral dilation of concrete. From the results, rings could improve the axial load-capacity, stiffness. And the way of installation and fabrication is very fast and simple, which is a good solution for site operation.Based on the fourth strength theorem and the failure parameter equation of concrete compressive in the three directions and relative factors, and induced the confinement index of hoops, the capacity formulas results calculated are in good agreement with the literature data and it shows that it is feasible for the CFST. The mechanical behavior of CFST confined by rings are analyzed under axial compression, combined compression and bending based on ABAQUS numerical simulation. Influence factors of strength of concrete, diameter to thickness of steel tube, stirrup reinforcement ratio for axial compression bearing capacity, and specially for compression and bending bearing capacity influence factors include eccentricity(or compression ratio), slenderness.In the last chapter, by simulating weld heat source and indirect coupling method, the dynamic changing process of stress and temperature during the soldering process are worked out. As a result, the bearing capacity of CFST was not affected by the welding residual stress.