Retrofit Strategies Using Braces for Pre-Northridge Steel Moment-Frame Buildings: An Analytical Study

This paper focuses on retrofitting strategies for tall pre-Northridge steel moment-frame buildings with vulnerable beam-to-column moment connections. Ten retrofit schemes of a 20-story building, originally designed according to the 1994 UBC, are developed in accordance with ASCE-41 by upgrading the brittle beam-to-column moment-resisting connections, or adding conventional/buckling-restrained brace elements to the existing moment-frame bays. Using nonlinear pushover and time-history analyses under near-source ground motion records from past earthquakes and synthetic ground motion records from three large-magnitude scenario earthquakes, the retrofit schemes are compared against the baseline model. While the baseline model is a total loss in 1331 of the 4014 scenario earthquake analysis cases, the worst of the braced retrofit schemes experiences a total loss in fewer than a third of these cases (426), clearly demonstrating the effectiveness of adding braces.