Seismic Retrofit of the Oakland City Hall, Oakland, California

The seismic repair and retrofit construction of the Oakland City Hall, originally constructed in 1914, has been completed, making it now the tallest seismically isolated building in the world. The steel frame building with masonry infill walls experienced extensive damage in the 1989 Loma Prieta earthquake, and has since been the focus of an intensive process of testing, historical evaluation, dynamic analysis, retrofit design, and construction, culminating with the installation of seismic isolation. Because there were no specific applicable code provisions to guide the analysis or strengthening of steel frame structures with fenestrated masonry infill, the design approach was based on the measured capabilities of the existing materials, and on the unreduced seismic response of the isolated superstructure. This "performance-based' approach was used throughout the design phase. The governing criteria was life safety during a strong earthquake.