Cyclic response characteristics of retrofitted moment resisting connections

Experimental studies were conducted in order to investigate the behavior of the weld in steel moment resisting connections. A total of forty seven reduced-scale subassembly model specimens were tested that represent welded moment resisting connections of the beam to box column. These specimens were used to study the following aspects in fabrication and retrofitting of moment resisting connections: Complete joint penetration (CJP) groove weld behavior, transversely loaded fillet weld behavior, grinding and rewelding influence on weld behavior, reinforcing of connection with T-stiffener and rib plates, strain rate effect on weld and material characteristics and electrode toughness effect on weld behavior. Following test result interpretations, five full-scale moment resisting connections of beam to box column were fabricated and tested. These models included one specimen fabricated with details of an outdated connection, two specimens with an improved CJP groove weld detail, and two specimens retrofitted by T-stiffeners. Each specimen was subjected to a standard quasi-static cyclic load pattern. Overall, the improved and retrofitted specimens performed well, achieving total (elastic plus plastic) story drift ratios of at least 4% radians in magnitude before experiencing 20% strength degradation.