Connection performance for seismic design of steel moment frames

Welded-flange-bolted-web connections were damaged during the Northridge Earthquake, and the SAC Steel Project was started to find solutions to the problems caused by this damage. The Connection Performance Team was one of several groups completing the project research, and this group examined all connection performance issues. A number of connections were evaluated, and three strategies were used to improve the seismic performance of different connections, An understanding of all yield mechanisms and failure modes for each connection type is required for application of these improvement strategies. Variations in yield mechanisms and failure modes obtained for different connection types are described, and the application of these modes and mechanisms to improve the seismic performance of three different connections is summarized. The three connections are the welded-flange-welded-web, reduced-beam-section, and bolted-flange-plate connections. These connections are all capable of providing good seismic performance with large plastic rotational capacity, but each connection requires evaluation of different modes and mechanisms and different balance requirements for good seismic performance. The strategies and procedures used for these connections are typical of those used for many other connections.