Retrofit of pre-Northridge moment-resisting connections

An experimental program was undertaken to evaluate methods to retrofit exis ting steel moment connections for improved seismic performance. Six full-sc ale subassemblages were tested under cyclic loading. Typical pre-Northridge connections were retrofit by the addition of either a bottom flange dogbon e or a welded bottom flange haunch. Retrofitted specimens were tested both with and without a composite floor slab. The tests showed poor performance of the bottom flange dogbone retrofit when the existing low toughness welds were left in place. Somewhat improved performance was observed when the bo ttom flange dogbone was combined with replacement of beam flange groove wel ds with higher toughness welds. The welded bottom haunch retrofit showed ex cellent performance on specimens with a composite slab, even though the exi sting low toughness beam flange groove welds were left in place. The presen ce of the composite slab appeared to help prevent fracture of the existing top flange weld in the haunch retrofit. This paper provides a summary of th e complete experimental program.