A wire rope is made of high-strength steel wires twisted into strands, and strands laid around a core; a strand is a single group of wires, used on its own as guy, messenger or prestressing strand. Ropes lift, haul and hold — cranes, lifts, winches, mooring and offshore work — and seven-wire prestressing strand carries the force in post-tensioned and precast concrete.
A wire rope is built in three stages. High-carbon wire, drawn to 1,770–2,160 N/mm² and usually bright or galvanized, is twisted into strands; the strands are laid helically around a core; and the core is either fibre (FC), which makes a flexible rope, or an independent wire rope (IWRC), which is stronger and resists crushing on drums. A construction is written as strands × wires per strand — 6x19, 6x36, 8x36 — with the core added: '6x36 WS-IWRC' is six strands of 36 wires in Warrington-Seale pattern on a steel core.
The construction is a choice between flexibility and wear resistance: many fine wires bend easily over small sheaves, a few thick ones resist abrasion and corrosion. Compacted strands, squeezed through dies before closing, give more steel in the same diameter and a smoother surface. Rotation-resistant ropes, with layers of strands laid in opposite directions, are used where a single-fall load must not spin, as on tower and mobile cranes. Ropes are lubricated during manufacture and must be kept lubricated in service.
Seven-wire prestressing strand (PC strand) is a different product: six wires laid around a straight centre wire, made from high-carbon wire rod, cold drawn and then stress-relieved under tension to give low relaxation. Grade 270 (1860 MPa) strand of 12.7 and 15.2 mm is the workhorse of post-tensioned slabs, bridges and precast hollow-core planks. Galvanized strand to ASTM A475 is used for guying, earth wires and messengers.
The Gulf's ports, offshore oil and gas, construction cranes and marine industry make it a large market for wire rope, most of it imported from Europe, Korea, China and India and held by regional stockists who also cut, socket and splice slings. Post-tensioned flat slabs are the common floor system in GCC high-rise and car-park construction, which makes PC strand a steady import. Ropes in lifting service are inspected and discarded to ISO 4309 and the lifting regulations of each country.
Ropes are ordered by nominal diameter, construction, core, wire grade, finish (bright or galvanized), lay (regular or Lang's, right or left) and length; the minimum breaking force for that combination is given in the rope standard or the maker's catalogue. PC strand is ordered by nominal diameter and grade; the strand table gives the ASTM A416 sizes.
Full dimensions: Seven-wire prestressing strand sizes (ASTM A416, Grade 270)
| Region | Standard | What it covers |
|---|---|---|
| Europe | EN 12385-1 to -10 CEN-CENELEC |
Steel wire ropes — safety; part 4 covers stranded ropes for general lifting, part 5 lifts, part 10 spiral ropes for structures |
| International | ISO 2408 ISO |
Steel wire ropes — requirements for general-purpose ropes |
| International | ISO 4309 ISO |
Cranes — wire ropes — care and maintenance, inspection and discard |
| Europe | EN 10264-1 to -4 CEN-CENELEC |
Steel wire for ropes |
| USA | API Spec 9A API |
Wire rope for oilfield and offshore service (drilling, well servicing and lifting); ISO 10425 is the international counterpart |
| USA | ASTM A1023/A1023M ASTM |
Stranded carbon steel wire ropes for general purposes |
| USA | ASTM A475 ASTM |
Zinc-coated steel wire strand (guy and messenger strand) |
| USA | ASTM A416/A416M ASTM |
Low-relaxation seven-wire steel strand for prestressed concrete — Grades 250 and 270 |
| UK | BS 5896 BSI |
High tensile steel wire and strand for the prestressing of concrete |
| Europe | prEN 10138-1 to -4 | Prestressing steels — still a draft; not published as an EN, so BS 5896 and national standards remain in use |
| Japan | JIS G3536 JSA |
Steel wires and strands for prestressed concrete |
| China | GB/T 5224 SAC |
Steel strand for prestressed concrete |
| India | IS 14268 BIS |
Uncoated stress-relieved low-relaxation seven-ply strand for prestressed concrete |
Grade equivalents and the standards bodies: Steel grades & standards
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