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How are the main cables of a suspension bridge made at the construction site?
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bridge
The multiple-span Seto Great Bridge over the Inland Sea, linking Kojima, Honshu, with Sakaide, Shikoku, Japan.
The main cables of a modern suspension bridge are constructed at the building site through a process known as cable spinning.12
This technique, invented by French engineer Louis Vicat, involves the following steps:
- Wire Transport: A traveling wheel or rope pulley system carries individual steel wires across the tops of the bridge towers to the opposite anchorage and back.12
- Strand Formation: The wheel carries a continuous cable strand from one anchorage, over the towers, and down to the midpoint of the bridge in a predetermined sag (catenary). Upon reaching the farther anchorage, a crew secures the strand and returns the wheel to lay a fresh strand.2
- Cable Assembly: Thousands of these parallel steel wires are spun together to build up the main cable.12
- Finishing: Once the desired thickness is achieved, the wires are bundled together and covered to protect them from corrosion.12
While early suspension bridges utilized linked wrought-iron eyebars, modern engineering relies on these parallel-wire bundles for their superior strength and efficiency.12