The main cables are scheduled for recoating beginning in summer 2010. To preserve the massive main cables for years to come, this critical three-year maintenance project will begin at mid-span on the west side Main Cable. Work will include erecting staging and building tent-like containment structures over 60-foot segments of the main cables. Inside the tent-like containment areas, crews will be cleaning the surface of the main cable, removing deteriorated coatings and roughing the entire surface to be ready to accept the new primer and topcoat, making any needed repairs, and undertaking any needed re-caulking as they go.

The work that will be performed is an over-coating paint job, so the crews do not have to clean the surfaces down to bare steel; instead the surface preparation will include 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 hand held vacuum tools. Great care will be taken to preserve the galvanizing on the cable wrapping wires as this coating is critical to preventing corrosion. Then the new paint system will be applied, and the tents repositioned along the main cable.

Crews will start at the roadway level at mid-span, and do the several hundred feet that are accessible at this location using a stationery scaffolding system with a tarp system to catch anything that may possibly get missed by the hand held vacuum tools. Once they move past the mid-span section and start to move higher on the cables, crews will use a powered suspended scaffold system, also with tarps. These sections will be about 60 feet-long as they move along the Main Cable.

The Main Cable Recoating Project includes:

1. Removal of the original packing from the cable band joints and caulking the grooves with a modern elastomeric sealant.
2. Reconditioning and/or replacement of specific cable shrouds.
3. Cleaning and Painting of the main cables, cable bands, and associated cable band bolts.
4. Painting of the hand rope system.

This project presents some significant day-to-day challenges:

• Performing work in an environment involving continuous traffic, without closing the Bridge to traffic.
• Working at a project site within a worldwide tourist attraction that attracts millions of tourists, pedestrians and bicyclists each year and with limited work areas, confined staging areas and restricted ingress and egress.
• Executing the work safely without affecting use of the Bridge by vehicles on the roadway and pedestrians, bicyclists and Bridge maintenance forces on the sidewalk.
• Performing work at high elevations and in extreme wind and weather conditions.

Original Main Cable Construction

The Golden Gate Bridge has two massive main cables which pass over the tops of the 746-foot tall towers. The main cables serve as the “hanger” for the vertical suspender ropes which, in turn, hold the Bridge’s roadway. The diameter of each of the main cable, including their exterior wire wrapping, is 36 and 3/8 inches and each main cable is 7,650 feet long. The total length of wire used in both main cables is 80,000 miles. Each of the main cables contains 27,572 galvanized wires which are bundled into 61 strands that contain 454 wires each. The combined weight of the main cables, vertical suspender cables and accessories is 24,500 tons.

Before the main cables could be constructed, for added safety and maneuverability, the workers built work platforms which hung under the area where the main cables would then be spun (pictured below left).

The wire used to build the main cables was laid by a loom-type shuttle that moved back and forth as it laid the wire in place that formed the cables. The spinning of the main cable wires was completed in six months and nine days.

Cable formers used vertical separators, in a frame, to keep each of the 61 strands in proper relation with one another—in vertical rows (pictured below middle).

Compacting machines were used to “squeeze” the cables into their circular shape. Each consisted of a frame which surrounded the cable with 12 hydraulic jacks around the circle (pictured below right).

Cable bands are attached to the main cable with large bolts at the point of attachment of each the 250 pair of vertical suspender ropes. Occasional re-tensioning of main cable band bolts becomes necessary because constant temperature and load changes in the main cable produce minute changes in the cable diameter, and those changes in cable diameter, together with temperature effects on the cable band itself, cause tension in the bolts to relax. In 1954, the cable band bolts were retightened for the first time since original construction.