A Retrofitting Framework for Pre-Northridge Steel Moment-Frame Buildings

A case study of retrofitting a 20-story pre-Northridge steel moment-frame building is presented. Twelve retrofit 4 schemes are developed with varying degrees of intervention. Three retrofitting techniques are considered: up5 grading the brittle beam-to-column moment resisting connections, and implementing either conventional or 6 buckling-restrained brace elements within the existing moment-frame bays. Detailed finite element models of 7 the base line building and the retrofit schemes are constructed. The models are analyzed under ground mo8 tions from three large magnitude simulated earthquakes that cause intense shaking in the greater Los Angeles 9 metropolitan area, and under recorded ground motions from actual earthquakes. It is found that retrofit schemes 10 that convert the existing moment-frames into braced-frames by implementing either conventional or buckling11 restrained braces are effective in limiting structural damage and mitigating structural collapse. In the three 12 simulated earthquakes, a 20% chance of simulated collapse is realized at PGV of around 0.6 m/s for the base 13 line model, but at PGV as large as 1.8 m/s through the retrofit schemes. 14