U.S. Experience – Seismic Rehabilitation Of Historic Structure With Dampers

The 145,000-sf (13,470 m2) building, built in 1910, is a torsionally nonsymmetrical structure comprised of a six-story portion adjacent to a two-story portion. The building is located in Northern California. There was significant concern that the building will not be able to withstand the level of earthquake shaking expected at the site because of two reasons: a weak and soft lateral force resisting system at the first floor level, and the inadequate confinement of reinforcement in the first story columns. To assess the performance of the structure, a detailed mathematical model of the building was prepared based on FEMA 253 guidelines. The analyses indicated that the building is not seismically adequate to withstand anticipated lateral (inertial) forces generated by earthquake excitations at the site. The structure will suffer substantial damage and possible collapse in the event of a major earthquake. The focus of the seismic rehabilitation was to address the major deficiency of the structure, namely the soft-story response of the building. Nonlinear fluid viscous dampers were placed at the first story level to reduce the seismic demand and obtain a more uniform fundamental response. Fluid visco-elastic dampers were strategically placed at one side of the building to reduce the torsional irregularity of the building. Finally, the first story interior columns supporting the six-story portion of the building were wrapped using fiber-reinforced polymer composite (FRP).

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