Kit Miyamoto, M.S., S.E., Amir Gilani, PhD, P.E., Lon M. Determan, S.E., Robert Hansen, PhD, P.E.
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This paper presents the nonlinear seismic analysis, development, and implementation of an innovative seismic retrofit strategy for a six-story nonductile reinforced concrete 145,000-sf (13,470 m2) historic building. Dynamic and nonlinear static analytical results verified that the building had a weak soft-story with inadequate post-yield capacity, and large torsional response. The analysis indicated that the existing building is not seismically adequate to withstand anticipated lateral forces generated by earthquake excitations at the site. A “collapse prevention” performance upgrade for a 475-year return event was desired. Nonlinear fluid viscous dampers were placed at the first story level to reduce the seismic demand and obtain a more uniform response. Visco-elastic fluid viscous dampers were strategically placed at one side of the building to reduce the torsional irregularity of the building. The proposed cost effective, state-of-the-art retrofit will improve the seismic performance of the building.