Experimental study on typically designed double-sided plate-reinforced joints with middle columns

Abstract

Beam-to-column joints in seismic moment frames would directly influence the behaviours of the connected members. When reinforced joint configurations were adopted to shift plastic hinges away from the field welds, columns in seismic steel frames would suffer larger inner forces and should be specially checked to control yielding mechanics. However, there were only few investigations on reinforced joints with typically-designed columns in multi-story frames, which limited the comprehensive evaluation of seismic beam-to-column joints especially for the reinforced joint configurations. In this investigation, the seismic behaviours of the cover-plate joint and the flange-plate joint, which are collectively referred to as plate-reinforced joints, were evaluated experimentally. Tests of four double-sided plate-reinforced joint specimens, taken from prototype seismic steel frames that were typically designed and checked by the Chinese code, were conducted under anti-symmetrical cyclic loads on the beam ends with axial forces in the columns. The test results were analysed to consider the seismic performances of the connections and members in the plate-reinforced joints, summarizing the characteristics of the failure modes, the resistance and the ductility. Specially, the seismic behaviour of the middle column with axial force, as well as the panel zone, was analysed. According to the test results, the flange-plate joints were more sensitive to the quality of the field complete-joint-penetration welds between the reinforcing plates and the column flanges than the cover-plate joints. The middle columns in typically-designed seismic frames by the Chinese code may not guarantee satisfactory seismic performances in the joint regions, and the panel zone that was designed based on the Chinese code might not allow the beam section to reach the plastic moment although it could effectively contribute to the joint deformability. Based on this study, practical recommendations for seismic design of connections and members in plate-reinforced joints were proposed.