Michael Gemmill, PARADIGM Structural Engineers, Inc.
Kurt Lindorfer, PARADIGM Structural Engineers, Inc.
H. Kit Miyamoto, Miyamoto International, Inc.
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The project consists of a two-story 150,000 s.f. data storage facility located in Santa Clara, CA. The site for the project, which lies within a region of high seismicity, is located approximately 16 km from the San Andreas and Hayward faults. The building owner desires an enhanced performance state for the building, exceeding that of the “essential services” criteria of the 1997 Uniform Building Code. The owner also desires reduced accelerations and displacements to protect sensitive equipment housed on the second floor. The mass of the building is approximately three times that of a typical office building with a similar floor plate. The lateral strength and stiffness of the structure are provided by 52 bays of special moment resisting frames (SMRF’s). The building’s displacement is controlled by 96 – 400 kip nonlinear fluid viscous dampers (FVD’s) installed within typical two story “X” braced frames.
In accordance with the Structural Engineers Association of California’s 1999 Recommended Lateral Force Requirements and Commentary (Blue Book), when a time history analysis is performed and dampers are incorporated to limit the story drift to an acceptable level, the building’s lateral force resisting system (LFRS) is designed for strength requirements only. This design philosophy leads to a relatively flexible building, thus resulting in lower building shear. The dampers reduce drifts to levels that would typically only be attainable with a much stiffer LFRS.
There are several benefits with using this design methodology, including, a decrease in structural steel cost and a decrease in forces on foundation elements, while additionally providing an enhanced performance state during a major seismic event.