Aerial spinning of main cables

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

How it is done

1. Build the catwalks and install the tramway: an endless hauling rope driven by a winch, carrying one or two spinning wheels that shuttle between the anchorages.
2. Set up wire reels and an unreeling station with tension control at the anchorage; join wire coils end to end with ferrules into a continuous wire.
3. Each pass of the wheel lays a loop of wire across the full length, around the strand shoe at the far anchorage, and the wires are placed in strand-forming frames along the catwalk.
4. Control sag: in traditional spinning each wire or group is set to a guide wire at night; in controlled-tension spinning the wire is laid at a set tension so that mainly strand-level adjustment is needed.
5. When a strand reaches its wire count (typically 250–550 wires), band it, lift it into its place in the saddles and splay castings, and adjust its sag against the reference strand at stable night temperature.
6. After all strands are placed, compact the cable with a hydraulic compactor to a void ratio of about 18–20 %, fit cable bands, then wrap and dehumidify.
7. Record wire counts, splice positions and strand sag readings as the cable's as-built record.

Key numbers

• Wireabout 4.9–5.4 mm galvanised, 1,570–1,770 MPa (higher grades on recent bridges)
• Strandsabout 250–550 wires each; a long-span cable has some 10,000–35,000 wires
• Golden Gate27,572 wires per cable in 61 strands
• Compacted void ratioabout 18–20 %
• Programmetypically 5–12 months for the pair of main cables of a long span
• CableUSD 8,000–15,000 per tonne installed (indicative)

Choosing it

• Choose aerial spinning when the cables are very large or the access route makes heavy PPWS reels hard to deliver; wire coils are light and can go anywhere.
• Prefer PPWS when cable erection is on the critical path and a strand fabricator is available: factory strands need far fewer hauls and less weather-sensitive work at height.
• Compare programmes on modern controlled-tension spinning, which removes much of the night-time wire-by-wire adjustment that made traditional spinning slow.
• Weigh the contractor's experience: few firms now keep spinning crews and equipment, which can outweigh any material cost advantage.

Plant, pace and money

Risks and controls

Origins

Louis Vicat developed in-situ spinning of wire cables in France around 1830, and John A. Roebling refined it in the United States; the Brooklyn Bridge (1883) was the first with steel wire spun in place.

Examples

Brooklyn, Golden Gate, Verrazzano-Narrows, Humber and Great Belt East were spun; by contrast Akashi Kaikyo and Xihoumen used PPWS.

Case studies

Related methods

Further reading

Gimsing and Georgakis · Steinman and Watson, Bridges and Their Builders