Nob Hill Condominiums, Seismic Evaluation and Retrofit

overview

Located at 1170 Sacramento Street in San Francisco, the 19-story Nob Hill Condominiums offer 71 luxury residences atop three levels of underground parking. Designed by John Carl Warnecke and T.Y. Lin and built in 1963, the building exhibits modernist formalism features such as an arched colonnade base and prominent vertical bay windows.

We provided structural engineering services to evaluate the building for seismic vulnerabilities and worked closely with the homeowners to present our findings and show how we could design a scope of retrofit work that would address the most critical vulnerabilities while allowing all residents to remain in their units, preserving building aesthetics and respecting the self-funded nature of the project.

Key collaborations included working with design partner KL Structures to maximize the effectiveness of the fiber-reinforced polymer (FRP) reinforcement, careful scheduling with Herrero Builders to stage outages of the stair and elevator cores that were a focus of the work, and the collaboration of Page & Turnbull and FD Thomas to develop a finish for the reinforced components that met fire code requirements and made the finished work nearly invisible to the untrained eye.

highlights

• Our team performed preliminary ASCE 41 Tier 1 seismic evaluations and Tier 2 detailed checks of structural elements.
• We prepared construction documents for a scope of voluntary seismic improvements heavily utilizing carbon-fiber reinforced polymer (FRP) for the replacement of the bay window units for the entire façade.
• We assisted ownership with integrating the proposed seismic strengthening measures to preserve the formalist architectural features and facilitate design review by the San Francisco Planning Department.
• Despite the COVID-19-related challenges, construction was safety and quickly executed during 2020 and 2021, making the lack of residential unit impacts all the more important.
• We continue to provide ongoing engineering support for maintenance and improvement projects as the building revitalizes itself for decades more as a landmark and premier residence atop one of San Francisco’s iconic hills.