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Spinning the Main Cables
By mid-1935, the north and south towers stood ready to support the two main cables. Each of the cables measured a little over 3 feet (about 1 meter) in diameter and weighed 12,000 tons. They were far too heavy to carry across the Golden Gate Strait on barges and lift up to the tops of the towers.
The cables were constructed high in the air using a process called cable spinning, which was invented by John A. Roebling in the 1800s. The company he founded made cables for the Golden Gate Bridge.
To spin the cables, workers pulled a wire, about as thick as a pencil, from the concrete anchorage at one shore, up and over both towers, and on to the other anchorage. The wire was then secured and sent back. It took many back-and-forth trips to place the 27,572 wires that are in each cable. Individual wires were grouped into heavier strands and compacted together to form the finished cable. The spinning of the cables took just six months and nine days, setting records for speed and efficiency.
The entire weight of the roadway deck crossing the Gate could then be suspended from the two cables – that's why it is called a suspension bridge. |