Performance‐based earthquake engineering was utilized to ascertain the seismic performance of a group of hospital buildings located in the regions of high seismicity in Southern California. The structures were designed and constructed in early 1970’s per the applicable building codes at the time of construction. Seismic evaluation of the structures, per current version of California Building Code or FEMA’s seismic evaluation procedures, indicated that buildings had severe structural deficiencies and would not survive the type of ground shaking anticipated at the sites. The design team developed an evaluation procedure and acceptance criteria for the buildings. The hospital complex consisted of a large four‐story structure and two adjacent one‐story buildings. Different framing systems were used to provide resistance to lateral loading for the three buildings. The four‐story structure used Pre‐Northridge connections and small wide flange column sections. It was supported on a one‐story reinforced concrete basement. The owner initially investigated adding full‐length cover plates to the majority of the columns. The retrofit cost and loss of functionality proved prohibitive. However, nonlinear response history analysis showed that when supplementary damper elements were strategically added to the building, the building response would markedly improve, and the story drifts and member flexural rotations were significantly reduced. For this structure, three performance objectives were developed. They included limiting: story drifts, steel member plastic rotations, and the lateral displacement of the first floor. One of the single story structures had masonry walls placed asymmetrically along the perimeter and showed large torsional response. The torsional response and story drifts were controlled by adding stiffness elements along the perimeter. The rehabilitated structures would meet the current seismic codes.
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