Prefabricated parallel wire strands (PPWS)

How bridges get built · Cable-supported and arch bridges · Prefabricated parallel wire strands (PPWS)

Also called: PPWS method, prefabricated strand erection

How it is done

Fabricate strands in the factory: bundle 61, 91 or 127 galvanised wires in hexagonal packing with a coloured marker wire, cut to the exact length measured under standard tension, and cast sockets at both ends; proof-load the sockets.
Ship strands on reels in erection order; set up the reel stand with a back-tension brake at one anchorage.
Haul each strand across the catwalk on rollers with a hauling rope and carriage, keeping it untwisted (follow the marker wire).
Lift the strand off the rollers into the tower saddles and splay saddles with shaping devices, and seat the sockets on the anchorage rods and shims.
Adjust the sag of each strand against the reference strand at night when the temperature is stable, using shims at the anchorage.
Repeat for all strands in the planned order, then compact the hexagonal bundle into a circular cable and fit cable bands.
Wrap and dehumidify as for spun cables.

Key numbers

Strand61, 91 or 127 wires of about 5.0–5.8 mm; 1,770–1,960 MPa wire on recent bridges
Strands per cableabout 100–300 (Akashi Kaikyo: 290 strands of 127 wires per cable)
Strand weightroughly 30–90 t for spans of 1–2 km
Haulingone strand across the span in a few hours; a full cable in 2–4 months
Compacted void ratioabout 18–20 %
CableUSD 8,000–15,000 per tonne installed, comparable to spinning at large scale (indicative)

Where it fits

Suspension spans 500-2,000 m; sites where cable erection time is critical.

Where it does not

Spans so long that strand reels become unmanageable; sites without a strand fabricator.

Choosing it

Choose PPWS over aerial spinning when cable erection is on the critical path: factory strands need fewer hauls and less weather-sensitive work at height.
Prefer aerial spinning when strand reels would be too heavy for the access route or handling plant, or the contractor's spinning experience is decisive.
Use 127-wire strands on long spans to reduce the number of hauls; 61 or 91 wires where reels must be light.
Fix the strand arrangement and socket layout at design stage; it sets the anchorage geometry.

Plant, pace and money

PlantReel unwinders, hauling ropes and winches, catwalk, socket seating jacks.

ProductivityA strand across the span in a few hours; a full cable of 100-300 strands in 2-4 months.

CostComparable to spinning at large scale, cheaper at medium scale.

Risks and controls

What goes wrong

Socket casting quality, strand twist during hauling, sag adjustment in temperature swings.

Quality assurance

Socket tests, sag survey at night at stable temperature, strand ordering plan.

Origins

PPWS was developed in the United States in the 1960s and first used for the main cables of the Newport Bridge, Rhode Island (1969); Japan adopted and refined it on the Honshu–Shikoku bridges, culminating in Akashi Kaikyo (1998), and it has been standard in East Asia since.

Examples

Akashi Kaikyo, Yi Sun-sin, Ulsan, Runyang, Xihoumen, 1915 Canakkale.

Case studies

Newport Bridge (Claiborne Pell)USA · 1969First suspension bridge with prefabricated parallel wire strand main cables; 488 m main span.

Akashi Kaikyo BridgeJapan · 1998127-wire strands of newly developed 1,800 MPa wire allowed a single cable on each side of the 1,991 m span.

1915 Çanakkale BridgeTürkiye · 2022PPWS main cables for the 2,023 m span, the longest built with prefabricated strands.