DESIGN AND RESEARCH ON STEEL TUBE COLUMN-RC FRAME TRANSFER JOINTS

Based on the traditional transfer form of steel tube columns and reinforced concrete (RC) frames, a new type of the transfer joint with good applicability was proposed. The longitudinal reinforcing bars of the RC column were welded to the steel pipe walls in the connecting region and the longitudinal reinforcing bars of the RC beams were welded to the flanges of the steel brackets. The downward insert length of the steel tubes was small within the transfer joint. Therefore, the effect of saving steel material was obvious. By using the laminated connecting detail at the flange of the H-section steel, the welding problem for the reinforcing bars of RC beams could be solved, and the influence of the eccentric force on the flanges could be simultaneously reduced. In the Key Laboratory of the Ministry of Education of Tsinghua University, four scaled models were tested for the transfer joints. The nonlinear finite element software Marc was used to analyze the mechanism of the transfer joints. The results show that under horizontal cyclic loading, when the specimens were loaded to the maximum displacement, the concrete at the end of the H-section steel was crushed and peeled off, and the longitudinal reinforcing bars were bent significantly to form a plastic hinge. The number of concrete cracks at the top of the frame column was small, and the frame column was basically intact at the end of the test. The pipe wall at the bottom of the steel tube column may have yielded, but the out-of-plane deformation on the steel tube column and joint region did not occur. The load-displacement hysteresis curves of the test specimens were full and had good deformability. The maximum stress of the steel tube column appeared near the top of the frame, and the stress of the transition section was lower than that of the steel tube column. When the ultimate deformation was reached, the H-section steel, inner ring plate and vertical stiffeners had lower stress and were in the elastic state. The steel tube column-RC frame transfer joint has good technical and economic performance, and can achieve the seismic performance target of “strong joint and weak component”.