The fog and sunrise one: The fog makes a regular appearance as part of the bridge experience, making painting even more challenging.
©Golden Gate Bridge, used with permission,
www.goldengate.org ORIGINAL MAIN
CABLE CONSTRUCTION One of several current maintenance projects underway since earlier this year is the complex repainting of the two 7,650 foot-long massive main cables. During the original construction, the spinning of the main cable wires was contracted to John A. Roebling’s Sons, of Roebling, NJ. Tis major task was completed in just six months and nine days. Tis is exhibited in the main cables that rise from their concrete anchorage housings at ground level and drape up and over the 746 foot-tall towers. Te cables support the vertical suspender ropes which, in turn, hold the roadway.
“The cleaning and resealing of the cable bands is detailed work requiring
hand tools and patience.” – Herbert Gabriel, Member of GGB Maintenance Crew
Working with protective gear and in containment tents, painters clean and prepare the main cable surface.
Te diameter of each main cable is a little over 3 feet and is comprised of 27,572 galvanized steel wires which are in turn bundled into 61 strands that contain 452 wires each. Te total length of wire used in both main cables is 80,000 miles. During the original construction, these strands were compacted in place and the exteriors of the cables were tightly wrapped with 1/8” diameter galvanized wire thoroughly embedded in a protective lead paste.
MAIN CABLE CONDITION Over the nearly 75 years since the span opened, the main cables have been inspected periodically and found to be in good condition. Further, they have been maintained over the years through the on-going maintenance program which has included the spot painting and the retightening of the cable band bolts in 1954 and again in the 1970s. Trough inspections, it was determined that the best practice at this time would be to undertake a complete repainting of both of the main cables. Fortunately, based on the evaluation of the main cable exterior condition, the extent of cable repair necessary at the Golden Gate Bridge is minimal. Tis is due to a combination of the exceptional quality of the original construction and the ongoing maintenance program – both of which have contributed to the Golden Gate Bridge withstanding extreme environmental conditions over the past seven decades. Inspections did indicate that the exterior paint coating system has passed the end of its useful life but the exterior wrapping wire is in good condition, requiring only minor localized repairs that can be done by hand. Additionally, the caulking at the cable bands, from which the vertical suspension cables hang, must be replaced and a new and modern elastomeric coating will be applied.
MAIN CABLE PAINT JOB Based on this determination and before the repainting could get underway, bridge engineers had to evaluate what steps would be required in the repainting process to best protect them from corrosion for decades to come. For some suspension spans, cables in poor condition can
require complete removal and replacement of the protective exterior wire wrapping — a process that involves using heavy and cumbersome wrapping machinery, as well as complex access systems consisting of continuous, temporary catwalks suspended just below the cables and spanning from tower to tower — somewhat reminiscent of the equipment needed during the original cable spinning operations. But, fortunately the work
20 NOVEMBER-DECEMBER 2011 WIRE ROPE EXCHANGE
©Golden Gate Bridge, used with permission,
www.goldengate.org
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