Experimental Research on Seismic Performances of Bolt-Welded Hybrid Joints for Concrete-Filled Square Steel Tube Columns with Steel Beams

The joints of concrete-filled steel tube columns with steel beams have been widely used in engineering, which meet the development requirements of prefabricated structures. However, it has been found that welding seams between steel beams and column walls were easy to fracture in earthquakes resulting in structural damage. Therefore, combined outer rib ring plates with the through-diaphragm connections, a new kind of bolt-welding hybrid joints for connecting concrete-filled square steel tube columns and steel beams, with upper ring plates and lower through-diaphragms was proposed. The failure modes, hysteretic performances, ductility and energy dissipation capacity of the five joint specimens with different connection types, column forms and vertical rib sizes were analyzed through quasi-static loading tests. The results showed that the proposed new joints had good seismic performances and could meet the design criteria requirement of "strong columns and weak beams". The equivalent viscous damping coefficient of the joints was more than 30% higher than that of full-bolted joints. Compared with the ring plate joints, the upper ring plate and lower through-diaphragm joints had better ductility, and the concrete-filled steel tube columns could effectively improve the bearing capacity and stiffness of the joints. Changing the thickness of the vertical rib plate and using full-bolted connections had a significant influence on the failure mode of the joints.