![]() Six instrumented braced steel buildings were found to have little or no damage, although ground shaking intensities at those locations were reportedly mild (Naeim, 1997, 1998). The Problemĭue to the relative lack of popularity of braced frames, the Northridge earthquake did not expose many braced frames to intense ground shaking. Unfortunately, some of the issues that affected the performance of moment resisting frames in the Northridge Earthquake (and were addressed in the SAC steel project) could also affect the performance of braced frames. These guidelines resulted in costly restrictions and regulations for steel moment frame construction, leading to an increase in steel braced frame popularity. In response, the Federal Emergency Management Agency (FEMA) funded research to generate moment-frame design and construction guidelines (a joint venture known as the SAC steel project). When the 1994 Northridge earthquake exposed unanticipated damage to steel moment resisting frames (SMRF), a period of uncertainty resulted regarding the reliability and proper design methods for SMRFs. and Japanese researchers showed the plastic energy dissipation of these systems to be poor so moment resisting frames dominated steel construction in high seismic regions. Past performance of braced steel frames and early research by U.S. Backgroundīefore the Northridge earthquake, braced frames were not the typical structural system utilized in non-industrial facilities. The post-Northridge era also saw the introduction of the buckling-restrained brace as a useful tool in seismic design. Simultaneously, lessons learned in the research on steel moment resisting frames, such as examination of expected material strength, were applied to the design of braced frames. Engineers changed their approach to analysis, proportioning, and detailing of braced frames to avoid connection failure and other unfavorable behaviors they had observed. In the case of braced frames, this led to a closer examination of the behavior of the system and its components at large drifts. The Northridge earthquake exposed the need for a more considered approach to seismic design.
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