Seismic Behavior Testing of Joints Reinforced by Sleeves Between Circular CFST Columns and Steel Beams

To solve the hidden danger of joints using single-direction bolts under seismic loads, this paper proposed joints reinforced by sleeves between circular concrete-filled steel tubular (CFST) columns and steel beams. Considering the joint construction and beam-to-column stiffness ratio as the main parameters, ten half-scale joint specimens were designed. The quasi-static test of the specimens under low cyclic reversed loading was completed by employing column end loading. The failure process and failure mode of the specimens were observed, and the hysteretic curve, bearing capacity, ductility and energy dissipation capacity, as well as strength and stiffness degradation of the specimens were analyzed. The damage law differences of the weld and bolt-weld joints reinforced by sleeves and the traditional joints using bolts were systematically compared using different influence factors, and the calculation methods of the ultimate bending moment of the joints were also provided. The test results demonstrate that the failure modes of joints are decided by the joint construction and the stiffness ratio of beams to columns. The bolt-weld joints reinforced by sleeves can prevent the occurrence of bolt relaxation, bolt fracture, and weld cracking and can meet the seismic design requirements of "strong joint, weak member". The connection stiffness and the strength of joints reinforced by sleeves are enhanced, and the joints change from having a semi-rigid connection to a rigid connection, because the moment and shear force are undertaken by both welds and bolts. Compared with the traditional joints using bolts, the joints reinforced by sleeves exhibit higher bearing capacity and safety reserve. Their equivalent viscous damping coefficient, angle ductility coefficient, elastic and elastic-plastic interlayer displacement angle all meet the requirements of the code, and their seismic performance indexes are satisfactory. Moreover, the calculation results of the ultimate bending moment of the joints are in good agreement with the experimental results, indicating that the method can be used for the design and calculation of the proposed joints. © 2021, Editorial Department of China Journal of Highway and Transport. All right reserved.