Hi-Tech Seismic Retrofit Solutions Compared for a Public Adminstration Building: Fid-Bau Portal

Hi-Tech Seismic Retrofit Solutions Compared for a Public Adminstration Building

Huang, Sampson / Skokan, Matthew / Islam, Saiful / Oguzmert, Metin / Cranmer, Ross D. / Caraig, Gerald

This paper describes the seismic retrofit of the Huntington Beach City Hall Administration Building located in Huntington Beach, California. The existing 6-story 71,000 square foot structure was constructed circa 1971 and is located in close proximity to the Newport-Inglewood fault. The lateral system for the building consists of a non-ductile reinforced concrete beam-column moment frame system in each of the principal building directions with concrete shear walls at the stairwells. The building is supported on a pile foundation system. A preliminary evaluation of the building revealed several seismic deficiencies, including the following: (1) non-ductile detailing, such as strong beam-weak column configurations and lack of column and beam confinement reinforcement, (2) flexible lateral system with excessive building deflections, (3) inadequate shear capacity of the beam-column joints, and inadequate strength of the shear walls at the stairwells. In addition to addressing the structural seismic deficiencies of the existing building, the City of Huntington Beach required that a seismic retrofit solution be developed that is: (1) aesthetically acceptable, since it is a large building occupied by city staff and frequently visited by the public, (2) non-intrusive, (3) minimizes interior construction work, and (4) allows open views for the building occupants. After considering several alternate retrofit schemes, which included adding exterior and/or interior concrete shear walls and exterior conventional steel braced-frames, two hi-tech seismic retrofit solutions were proposed: (1) Addition of exterior buckling restrained steel braced frames and (2) Addition of viscous dampers in exterior conventional steel braced frames. The intent of both solutions is to reduce the deformation demands on the existing non-ductile concrete frames to below acceptable levels; however, the two proposed retrofit solutions accomplish this from two different approaches. The solution utilizing the buckling restrained braces provides added stiffness to the building, whereas, the viscous damper solution provides added damping to the building. In both cases, the new buckling restrained braces or viscous dampers were incorporated into a new concrete beam-column frame connected to one-bay at the exterior of the building on all four sides of the building.