Static Behavior Of End-plate Joints For Concrete-filled Thin-walled Steel Tubular Frames

Concrete-filled thin-walled steel tube possess high capacity, good plasticity and toughness, facilitate production and construction, good fire resistance and economy.Presently, the studies on cold-formed steel components were relatively mature, but concrete-filled thin-walled steel tube was rare. It is lack of design method for concrete-filled thin-walled steel tube, which prevented this new typed structure promotion and application in practice engineering. therefore, The experimental and theoretical studies of endplate joints for concrete-filled thin-walled tubular frames have important significance.In this paper, static experiments, theoretical calculation model of endplate joints to concrete-filled thin-walled steel tubular columns were studied. The main results could be summarized as following:(1) Nonlinear finite element analysis(FEA) models were proposed to analyze the mechanical behavior of endplate joints to square steel tubular columns with steel ribs by ABAQUS software. The calculated results were verified by the test results. The stress distribution and deformation of each component were analyzed by FEA. The mechanism of the joints were also discussed.(2) In order to investigate the performance and failure modes of endplate joints for concrete-filled thin-walled tubular frames, an experimental programe was conducted involving four side-column connections subjected to monotonic loading. Moment-rotation relationships of the tested connections were obtained and their performance was evaluated in terms of their stiffness, moment capacities and ductility. It is showed that: although the thickness of steel tube is small, this type joints, which are semi-rigid and partial strength, still have reasonable strength, stiffness and ductility by taking reasonable measurements. The ultimate rotations were exceeded 0.044rad, not less than 0.03rad of the design requiements of FEMA-350, and could be relably and safely used in moment-resisting composite frames.(3) Nonlinear finite element analysis(FEA) models were proposed to analyze the mechanical behavior of endplate joints for concrete-filled thin-walled tubular frame by ABAQUS software. The calculated results were verified by the test results. The stress distribution and deformation of each component were analysied by FEA. The mechanism of such joints were also discussed. Parametric analysis on the moment-rotation curves of this type joints were performed. The results show that the thickness of endplate, thickness of columns, diameter and pre-tension of bolts have obvious influence on the behaviour of connections. For sway or non-sway frames, flush endplate joints for concrete-filled thin-walled tubular frames were semi-rigid and partial strength; extended endplate joints for concrete-filled thin-walled tubular frames were semi-rigid and partial strength or full strength.(4) Based on the test results and other research studies, the reasonable constructional measurements, in order to enhance the connectivity of this type joints, were presented, which were suitable to used in structural design and construction.