Amir Gilani, Miyamoto International, Inc. West Sacramento CA/USA
Kit Miyamoto, Miyamoto International, Inc. West Sacramento CA/USA
Nahib Youssef, Nahib Youssef & Associates, Los Angeles, CA/USA

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Seismic performance of a multi-story hospital structure located in Southern California was evaluated using performance-based earthquake engineering. The uppermost eight stories of the superstructure use steel framed construction, whereas reinforced concrete framing is used for the lowest floor (L2) and the four sub-grade parking stories. The building is rectangular in plan, has a typical story height of 3.6 m (11.8 ft) and a total floor area of 12,000 m2 (130,000 ft2). In both lateral directions, steel moment-resisting frames using Pre-Northridge connection details were used to resist lateral loading. Reinforced concrete framing comprise the lateral load resisting system for L2 and parking levels. Provisions of FEMA 273 [FEMA 1997], FEMA 351 [FEMA 2000], and OSHPD-approved design procedure [NYA&MI 2003] were used to evaluate the expected seismic performance of the structure in the existing configuration subjected to a 475-year seismic event. A comprehensive three-dimensional mathematical model of the structure was prepared and subjected to acceleration histories generated to match the site-specific response spectrum. Response was evaluated using nonlinear analysis. Structural performance did not meet the design requirements for story drifts and nonlinear flexural rotations. To enhance the building response, the analytical model was modified by adding fluid viscous dampers attached to new exterior frames. Analysis of the structure in the upgraded configuration indicated that the performance requirements were satisfied. Parametric studies were conducted to investigate the effects of variation in key parameters, such as damper coefficients, nonlinear hinge properties and soil-structure interaction, on the response of the retrofitted structure.