Cyclic performance of repaired welded unreinforced flange-bolted web connections

Three post-earthquake repair techniques were developed to restore or upgrade the capacity of fractured pre-Northridge beam-column connections. Four full-scale beam-to-box column connections were prepared and cyclically loaded until fracture. Three of them fractured at the bottom flange under the drift of about 2 to 3%, and one fractured at the top flange. The bottom flange fractured connections were then repaired and tested again. The results showed that the combination of applying supplemental welds at the web and attaching wing plates to the bottom flange increased the strength and ductility. The repaired connection fractured at the top flange at the drift amplitude of 4%. When inner flange stiffeners were additionally applied on the top flange for enhancement, the stress concentration was moved to the beam from the connection and resulted in a most ductile behavior among the repair techniques. The weld-free repair technique, which attaching the reduced section plate at the bottom flange by high tension bolts, exhibited a comparable performance to the connection repaired by adding additional welds and wing plates. Overall, the combination of attaching wing plates and inner stiffeners at the bottom and top flanges, respectively, would provide reliable performance.