“With the CMGC method, you’re allowed to bring the contractor on during the design phase and then they get to work with you as part of the design team and provide input on design with respect to constructibility,” says John Eberle, district engineer with the Golden Gate Bridge, Highway and Transportation District, the agency in charge of maintaining the bridge.  

Halmar was brought on board when the design was about 85% complete. The firm is currently developing means and methods for implementing the retrofit, including trying to figure out the best way to access the bridge during construction when officials are projecting about 200 crafts people per day during full peak. 

Halmar was required to defer to the agency for comment. In an Instagram post, estimator Christiana George noted that 3D printing is one of the tools being used to examine various scenarios.

“The bridge is operating with more than 100,000 vehicles per day, along with pedestrians and bikes on the sidewalks, as well as our own crews, so Halmar has to come up with how they're gonna get workers out to the site without impacting traffic and pedestrians, and that's pretty challenging,” says Eberle.

The project is the last phase in a series of seismic upgrades on the bridge that began after the 8.3 Loma Prieta earthquake struck the California Central Coast along the San Andreas Fault System in 1989. Analysis has found that 8.3 is the maximum credible earthquake that could strike the region. 

“While the Golden Gate Bridge can safely withstand a large earthquake today, the final phase of the seismic retrofit will help ensure the bridge remains in service in the aftermath of a major natural disaster and will help our region respond and recover in the days, weeks, and months that follow," says 

Phase 1 upgrades to the historic structure began in 1997 and centered on the Marin (north) Approach Viaduct. The $79-million project consisted of structural upgrades and strengthening of structural components and the modification of structural responses to better respond to strong motions without damage.  

Phase 2 began in June 2001, and was completed in July 2008. The $189-million project encompassed structural retrofit of the south approach viaduct, south anchorage housing, Fort Point arch, and south pylons. 

Phase 3A ran from 2008 to 2014 and included the retrofit of the North Anchorage Housing and Pylon N1. The $125-million project was funded using a combination of federal funds along with regional and state earmarks. 

This current $870-million project, known as 3B1, is funded with $400 million through a federal bridge investment program, $200 million from the California Dept. of Transportation, and $270 million in district capital reserves. 

The highlight of this phase is a retrofit of the two 746-ft-tall towers. At the base of the towers, crews will bolt on 2-inch-thick steel plates that are about 40 ft tall to strengthen the perimeters, and strengthen the transverse tower struts at the roadway level. 

Crews will add 28 energy dissipation devices on the two 1,125-ft-long side spans. Fourteen of the devices will be installed on each of the side spans where they connect to the stiffening trusses at the roadway level. The dissipation devices are made out of stainless steel, weigh up to 26,000 lb and can stretch up to 20 ft depending on their configuration.

“The devices will dissipate energy from an earthquake so that that force will not be imparted into the stiffening truss; they’ll reduce the force so you don't have to retrofit every single member of the bridge,” says Eberle. 

In the stiffening trusses, located below the roadway deck, crews will remove and replace the top lateral bracing system and strengthen some of the connection.

One of the last elements of Phase 3B1 is the abatement of the existing paint system from the 1930s. Eberle says it contains about 68% lead by weight and that much of the bridge still has lead all over it. 

An example of the logistical challenge is the south tower, which is 1,000 ft offshore. “To retrofit it, crews have to get down there and then get inside the tower and do very surgical work, removing existing fasteners and putting on new steel plates without damaging or creating havoc with the existing structure and the stresses in it," says Eberle.

Eberle says the district plans to award a construction contract for the project by this December and then launch a notice to proceed in January. Halmar will likely be the general contractor, assuming the parties can agree on a price. If they cannot reach a price agreement, the project will go out to bid to other contractors. 

When 3B1 is complete in 2031, the district will begin 3B2, which will cost about $900 million and will concentrate on retrofitting the main 4200-ft-long span.