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This paper describes a case study of performance based seismic rehabilitation techniques used for a 1969 vintage concrete parking structure. A new 80,000ft2, two-story addition was planned for this existing 230,000ft2, six-story structure. The evaluation procedures followed both the FEMA 273 nonlinear static and dynamic analyses.
The building is separated into two structures with a 2-inch expansion joint. Concrete shear walls are located at each end of the structure in the transverse direction and along the middle of each structure in the longitudinal direction.
Three-dimensional nonlinear models were constructed using SAP 2000. The shear walls were modeled as beam-column elements with plastic hinges considering degradation effects. Soil-structure interactions were considered using the Winkler model. A capacity and demand spectrum was used to evaluate displacement demands and capacities.
The nonlinear static procedure revealed: 1) a lack of shear strength at the longitudinal shear walls, 2) possible pounding at the structural separation, and 3) absence of torsional redundancy in the longitudinal direction. The following retrofit measures were proposed to address the above issues: 1) provide fiber reinforced polymer to the shear walls to increase the shear capacity, and 2) provide fluid viscous dampers at exterior frame to reduce displacements in the X-direction and to add dynamic torsional stiffness. Nonlinear time history analyses were conducted to evaluate damping devices.