Viscous dampers at multiple levels for the historic preservation of Los Angeles City Hall

This paper presents a case study of a seismic rehabilitation strategy, utilizing passive energy dissipation devices, for the preservation of a historic structure. The subject building is the Los Angeles City Hall, a 460 feet tall steel frame with unreinforced masonry infill. The rehabilitation consists of installing 416 high damping rubber bearings and 90 flat sliding bearings at its base in conjunction with 64 nonlinear viscous dampers. This paper presents the rationale for supplementing base isolation with viscous damping devices. The sensitivity of the global building response to the introduction of supplemental energy dissipation is also investigated.