How Safe Are Pre-Northridge WSMFs? a Case Study of the SAC Los Angeles Nine-Story Building

This paper demonstrates a procedure for modeling, analysis, and evaluation of existing steel frame buildings of the type damaged in the 1994 Northridge earthquake. The procedure accounts for Northridge data and incorporates post-Northridge research. It is distinguished from more conventional procedures by the use of fracturing connection elements with randomly assigned rotation capacities. The study confirms and quantifies a number of observations from Northridge. Damage patterns are highly variable, but their global effects are predictable. Many steel frame buildings can sustain substantial damage and still satisfy criteria for “safe” response. Expected performance, however, is measurably less reliable than intended performance, and this has important implications for public policy and performance-based engineering.