In the immediate aftermath of the Northridge earthquake in 1994, steel buildings seemed to perform well. In the weeks to months following, however, extensive damage was found in special moment frame steel systems. As a result, FEMA allocated 10 million dollars to investigate, test and analyze materials, member connections, and structural systems in order to establish a better understanding of seismic structural systems, and recommend changes to building codes.
In the September 2019 SE University session, James O. Malley, SE, from Degenkolb Engineers, presented Changes to the Seismic Design of Steel Buildings. Jim reviewed how the damage caused to steel moment frames during the Northridge earthquake led to major changes in the design of steel structures. Jim outlined the new overall design philosophy which aims to develop inelastic mechanisms within designated structural fuses to dissipate the majority of the earthquakes energy. Jim also covered how seismic design requirements aim to satisfy this new design philosophy for the various structural systems.
During the session, Jim explained new language that was added in 2016 to AISC 341 in regard to columns that are common to intersecting frames. Research showed that in high R factor systems where columns are shared by intersecting frames, the 100/30 rule may not be adequate, especially for low rise buildings. Thus, language was added to ensure this potential simultaneous inelasticity is considered during design. In the 3 minute video below, Jim explains the reasoning for this code change.