Seismic Evaluation and Rehabilitation of a Three Story Pre-Northridge Steel Frame Essential Service Facility

The 1994 Northridge earthquake exposed the vulnerability of steel moment frame structures to seismic damage. This paper summarizes the performance-based seismic retrofit of a three-story steel moment frame building in the San Francisco Bay Area of California. The building is located within a few hundred feet of the Hayward fault and serves as an essential service facility. ASCE 41 was used in conjunction with FEMA 351 to assess the anticipated performance of the existing building and to evaluate several retrofit options. Retrofit options included: connection upgrades, the addition of either energy dissipation or buckling restrained braces, and combinations of these approaches. Various performance objectives were studied and varied from Life-Safety to Immediate Occupancy and included the evaluation of both structural and non-structural systems. Schematic level plans and associated estimate of probable cost were developed for each of the six schemes. After extensive discussions with the owner, an Immediate Occupancy level of performance at the DBE emerged as the desired objective for the retrofit. The strengthening scheme is currently in design development and will include the combination of connection upgrades and new buckling restrained braces. The design phase will employ non-linear static and dynamic analyses to evaluate the efficiency of the retrofit.