Stringing a Cable Strand

If you’ve ever visited the Golden Gate Bridge Welcome Center in San Francisco, you may have seen an exhibit of a cross-section of one of the orange cables that drape over the bridge’s towers. Each cable has a diameter of 36.5 inches, contains 27,572 tiny wires and measures 7,650 feet in length. The Bridge Project’s cable stays are much different. Instead of tens of thousands of tiny wires, each stay is made up of cable strands that have 7 woven wires and are covered in a durable rubber casing to prevent corrosion from exposure to the elements. Depending on the promixity to each tower, each stay varies in the number of strands with 49 for the closer ones ranging up to 109 for the farthest ones.

The video above shows a construction crew placing a cable strand in one of the longest stays that connects the tower to the last road-deck segment in the middle of the new bridge. A pilot line is lowered by a crew in the tower down the white cable pipe to the road deck. The crew members there attach a strand to that line, then it is pulled up by a winch to the tower. In the video, you can see that strand being guided on a blue disc-feeder as it is pulled up.

When the tower crew gets the proper length of strand, they stop the winch, then knock on the cables to give the road deck crew an audio ping to cut the strand on their end. They cut the strand, then lift the heavy strand into a cable receptacle on the road deck. Another pilot line on that end enables the strand to be properly placed in the right hole.

Looking at the receiving crew under the road deck, you can see all of the other individual strands that have already been placed. Each of these strands of cable can be individually “tuned” to help post-tension the road deck. Look for more on post-tensioning and how it works in a future weekly update.