April 3, 2006

Status of Golden Gate Bridge Seismic Retrofit Construction Project

The race against time continues as, according to the U.S. Geological Survey, there is a 62% probability of a magnitude 6.7 or greater earthquake striking the San Francisco Bay Area in the next 30 years. Immediately following the Loma Prieta Earthquake, the District initiated vulnerability studies for the Golden Gate Bridge. The studies concluded that the Bridge was vulnerable to a 7.0 or greater Richter magnitude earthquake with an epicenter near the Bridge — the Bridge is located between the San Andreas and Hayward faults. Once completed, the span will be able to withstand a quake with a nearby epicenter of 8.3 magnitude. It must be noted, that as of April 2006, the seismic retrofit of the Golden Gate Bridge is far enough along that the Bridge no longer faces the potential for collapse but until the entire retrofit is completed, the risk of significant damage to the Main Suspension Bridge remains.

The entire seismic retrofit construction project is estimated at $405 million. Several construction phases were established, with the most vulnerable structures being retrofit first. The seismic retrofit measures applied to all Golden Gate Bridge structures (click here to view diagram of retrofit measures) consist of various methods of structural upgrades and include both the strengthening of structural components and the modification of structural response of the structures so they can better respond to strong motions without damage.

Phase 1 - Retrofit of the Marin Approach Viaduct Structures
Phase 1 was funded using Golden Gate Bridge tolls. Construction began in August 1997 and the structural work was completed in December 2001.

Phase 2 – San Francisco Approach Viaduct Structures and Fort Point Arch

In June 2001, the second construction phase began. It is the most complex part of the project in terms of design and construction. A combination of federal, state and regional funds was authorized to complete this phase. The structural work for this phase is now being completed and final items, including tasks such as painting, are being completed this year. This phase encompasses structural retrofit of many different types of structures of the south approach: south approach viaduct, south anchorage housing, Fort Point arch and south pylons. Retrofit measures developed for each of these structures reflect their individual behavior under seismic ground motions and their interaction at points of interface while accommodating their already-in-place historic configuration.

Phase 3A -   North Anchorage Housing and Pylon N1

Phase 3A will be funded using a combination of federal funds along with regional and state earmarks. It is anticipated that construction bids will go out for Phase 3A in summer 2006 with construction underway by the end of 2006. This phase project will take approximately 3.5 years to complete.

Phase 3B – Main suspension span, Main Towers, South Tower Pier and Fender

Phase 3B will also be funded using a combination of federal funds along with regional and state earmarks. Phase 3B will begin in 2008 and also take approximately 3.5 years to complete.

Seismic retrofit measures for Phases 3A and 3B consist of strengthening foundations, installation of micropiles and rock bolts, construction of reinforced concrete shearwalls, replacement of the housing roof/roadway deck with a pre-cast concrete slab-on-steel stringer deck system involving nighttime lane closures, and other structural modifications.

Summary of Funding

Golden Gate Bridge
Seismic Construction Phases

Federal
Funds
($millions)

Other

Funds
($millions)

Total

Construction Cost

($millions)
Construction Timeline
Phase 1
North Viaduct Approach Structures
$0
$71
from Golden Gate Bridge tolls
$71

Completed in Dec. 2001

Phase 2
South Viaduct & Anchorage, Fort Point Arch, South Pylons

$98

$76
from regional &
state earmarks
$174
Schedule for completion in fall 2006
Phase 3a & Phase 3b
a: North Anchorage and Pylon N1
b: Suspension Span and MainTowers, South Tower Pier and Fender
$56
$104
from regional &
state earmarks
$160
3.5 years for each sub-phase to be completed once underway
TOTALS
$154
$251
$405