Construction methods · Cable-supported and arch bridges

Stay cable installation and tensioning

Modern stays are bundles of 15.7 mm greased and sheathed strands inside an HDPE pipe, installed strand by strand with a small winch and stressed one at a time with a monostrand jack (isotensioning), then adjusted as a bundle. Older and some Japanese bridges use prefabricated parallel wire strands or locked coil ropes installed whole.

How bridges get built · Cable-supported and arch bridges · Stay cable installation and tensioning

Also called: strand-by-strand installation, parallel strand stays, locked coil stays, stay stressing

How it is done

  1. Install the HDPE pipe between the deck and pylon anchorages on a pilot strand; feed the strands one by one through the pipe with a winch, seating the wedges at both anchorages.
  2. Stress each strand to the same force with an isotensioning jack referenced to the first strand; the bundle then carries the design force at the end of the cycle.
  3. Later adjust the whole stay with a multistrand jack; install dampers, cross-ties if specified, and the anchorage protection (wax or grease, caps).
  4. Measure forces by lift-off tests or by vibration frequency.

Where it fits

  • All cable-stayed and extradosed bridges.

Where it does not

  • Whole-stay lifts of heavy prefabricated strands where a deck crane is not available; skipping force verification.

Plant, pace and money

PlantStrand pusher or winch, monostrand and multistrand jacks, pipe handling frames, force measurement.
ProductivityA stay of 60-100 strands installed and stressed in one to two days by a specialist crew.
CostUSD 15-30 per kg of stay installed including anchorages.

Risks and controls

What goes wrong

  • Wedge seating failure, strand damage during pushing, wrong force sequence loading the pylon unevenly, pipe damage, fatigue at anchorages.

Quality assurance

Fatigue and static acceptance tests of the stay system (fib 30 / PTI), force records per strand and per stay, lift-off tests on a sample, anchorage inspection.

Examples

Freyssinet, VSL, DSI and BBR systems on most modern cable-stayed bridges.

Related methods

Cable-stayed cantilever erectionPylon construction: concrete, anchorage zones and geometryExtradosed bridge constructionCable wrapping and dehumidification

Further reading

PTI DC45.1 · fib Bulletin 30 · SETRA Cable stays guide

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