Construction methods · Cable-supported and arch bridges

Aerial spinning of main cables

A spinning wheel carries loops of 5 mm galvanised wire across the span between the anchorages, thousands of times, building the main cable wire by wire in strands of several hundred wires that are then compacted into a circular cable. The traditional method of American and European suspension bridges, still used for the very largest spans.

How bridges get built · Cable-supported and arch bridges · Aerial spinning of main cables

Also called: AS method, spinning wheel, wire-by-wire cable erection

How it is done

Hang the catwalk and a hauling rope; load wire reels at one anchorage.
The spinning wheel carries a bight of wire across, looping around the strand shoe at the far anchorage; the wire is adjusted to the correct sag on each pass.
Form each strand of 100-500 wires, band it, and place it in the saddles; when all strands are in, compact the cable with a hydraulic compactor to a circular section and install cable bands.
Wrap with wire or a polymer sheath and dehumidify.

Where it fits

Very long spans (over 1,500 m) where prefabricated strands become too heavy to handle; sites with the crew skill.

Where it does not

Spans where PPWS is faster and cheaper (most modern spans below 1,500 m).

Plant, pace and money

PlantSpinning wheels and tramway, catwalk, adjustment gantries, compactors.

ProductivityMonths; the Akashi Kaikyo cable took about a year with PPWS after trials.

CostCable USD 8,000-15,000 per tonne installed.

Risks and controls

What goes wrong

Wire sag errors, wire breaks, weather stoppages, wire corrosion before wrapping.

Quality assurance

Sag adjustment of every strand relative to a reference strand, wire counts, compaction diameter checks.

Examples

Golden Gate, Verrazzano, Humber, Great Belt East, Storebaelt; Chinese Xihoumen used PPWS.