San Francisco, CA
Golden Gate Bridge North Anchorage Housing
Following the 1989 Loma Prieta earthquake, the Golden Gate Bridge District conducted a seismic evaluation of this iconic span located less than 3 mi from the San Andreas fault. The District determined the bridge could not reliably survive a repeat of the Great 1906 San Francisco earthquake and elected to undertake a multi-phase retrofit of the structure and foundations.
In Phase III of the process, SGH provided construction engineering support for the North Anchorage Housing Seismic Upgrade on behalf of the General Contractor. This large reinforced concrete structure at the bridge’s Marin County landing provides both anchorage for suspension cables and support for the roadway.
The renovations entailed demolition and roadway replacement. Using a nonlinear static (pushover) procedure, SGH evaluated the structure’s service load stability and earthquake resistance during various construction stages and recommended strengthening and temporary bracing/shoring, as necessary. As part of this process, we determined the probability of earthquake closure of the bridge, which carries 40,000 vehicles per day, within the two-year construction period, enabling the contractor and the District to assess the acceptability of risk.