Scaffolding has arrived and containment construction is on deck for the first-ever renovation and repainting of the Golden Gate Bridge’s two main suspension cables.
Rich Niewiroski Jr.
The two main bridge cables top the
746-foot-tall towers and are 7,650 feet long.
The 24,500-ton main cables have not been completely painted since the storied bridge opened in 1937. Just over three feet in diameter, each cable is comprised of 27,572 individual galvanized steel wires wrapped inside a casing, which is painted for protection.
The main cables, constructed in 1935 and 1936, serve as hangers for the 250 vertical suspender ropes that, in turn, hold the bridge’s roadway 220 feet above the water. Each cable is 7,650 feet long and passes over the tops of the 746-foot-tall main towers.
"We redid the vertical suspender cables in the 1970s and the roadway itself in the 1980s, but this is the first time the main cables will be renovated in this manner," said Mary Currie, bridge district spokeswoman.
Access and Containment
Scaffolding for the three-year project was delivered Feb. 22 to midspan on the bridge and unloaded onto the west sidewalk. On the West Side main cable, fixed scaffolding is being assembled along the 400-foot-long segment from midspan south toward the San Francisco side of the span, according to the Golden Gate Bridge, Highway and Transportation District.
The Golden Gate Bridge, Highway and
Transportation District includes
38 painters for bridge maintenance.
The scaffolding and a tent-like containment structure will entirely surround or envelop the main cable in 60-foot-long segments. The containment structures will be moved along the 400-foot segment of the main cable as each 60-foot-long segment is completed.
The scaffolding will extend from the sidewalk level to about three feet above the main cable—about 25 feet tall, at its maximum, and six feet wide.
Workers will then spend up to six months renovating this portion of the main cable. After that section is completed, the scaffolding will be disassembled and reassembled along a 400-foot-long segment heading north from midspan toward the Marin side.
Workers will then renovate this segment of the West Side main cable. This 800-foot section alone is anticipated to take about a year to complete.
Once work is completed on the West Side main cable, work will shift to the East Side main cable, where the same system will be used.
Also, the higher portions of both of the main cables will be recoated using elevated platforms beginning this summer.
Surface Prep and Coating
Golden Gate Bridge work crews will undertake the following during the three-year renovation.
Inside the tent-like containment areas, they will clean the surface of the main cable; roughen the surface of the main cable, to prepare it to accept new paint; make any additional required repairs; re-caulk the main cable bands; and apply a new paint system.
The work that will be performed is an over-coating paint job, so crews will not have to clean the surfaces down to bare steel, the bridge district said. Instead, surface preparation will involve using hand-held vacuum-shrouded power tools while working inside the tents.
Any old paint that is not tightly adhered to the cable will be “sucked” into the vacuum tools. Great care will be taken to preserve the galvanizing on the cable wrapping wires, as this coating is critical to preventing corrosion, the district said.
Then the new paint system will be applied, and the containment tents repositioned along the main cable.
The job won’t be easy. The bridge will not be closed to traffic, and the worldwide tourist attraction draws millions of visitors each year.
The scaffolding will reduce the west sidewalk width from 10 feet to seven feet; bicyclists may be asked to walk their bikes through the work area.
The project site has limited work areas, confined staging areas and restricted ingress and egress, and the Bay Area’s notoriously unpredictable climate may have a substantial impact on production, officials say.
The bridge district is doing the project in-house, after planning to contract out the job at a cost of $30 million. The scaffolding is costing the district $100,000, reports the Marin Independent Journal.
The district has 17 ironworkers and 38 painters to maintain the bridge. Ironworkers replace corroding steel and rivets with high-strength steel bolts, make small fabrications for use on the bridge, and assist painters with their rigging. Ironworkers also remove plates and bars to provide access for painters to the interiors of the columns and chords that make up the bridge. Painters prepare all bridge surfaces and repaint all corroded areas.
"This is a great project for us to take on in-house, especially in the face of the financial challenges that so many public agencies are facing," Denis Mulligan, bridge general manager, told the Marin newspaper.
Keeping It Golden
Although details of the coating system were not immediately available, picking colors won’t be an issue. The Golden Gate Bridge has always been painted an orange vermilion color called "International Orange."
(The PMS code is 173, or the CMYK colors are: C= Cyan: 0%, M =Magenta: 69%, Y =Yellow: 100%, K = Black: 6%.)
Rejecting carbon black and steel gray, bridge designer Irving Morrow selected the orange because it blended well with the span's natural setting, the bridge district said. “If the U.S. Navy had its way, the bridge might have been painted black with yellow stripes to assure greater visibility for passing ships,” the district noted.
The paint protects the bridge from the air’s high salt content, which rusts and corrodes the steel components. The bridge was painted when it was originally built with a red lead primer and a lead-based topcoat, the district said.
Until 1965, only touch-ups were required. In 1965, advancing corrosion sparked a program to remove the original lead-based paint and replace it with an inorganic zinc silicate primer and acrylic emulsion topcoat. In the 1980s, this system was replaced by a water-borne inorganic zinc primer and an acrylic topcoat. Since then, the bridge has required only ongoing touch-up painting.