Stay cable and hanger replacement

How bridges get built · Finishing, articulation and maintenance · Stay cable and hanger replacement

Also called: stay replacement, hanger replacement, suspender replacement, cable renewal

How it is done

Investigate the cables: visual and sheath inspection, magnetic flux or acoustic monitoring for wire breaks, force measurement by vibration, and opening of selected anchorages; decide between local repair and partial or full replacement.
Analyse every replacement stage: the structure with one cable (or one symmetrical pair) removed, traffic and wind limits for each stage, and the forces in the neighbouring cables and the pylon; design temporary cables or deck support where one cable cannot be removed safely.
Survey the anchorage interfaces: new cable systems often have different anchorage sizes, so check fit in the pylon and deck anchor boxes from measurements, not old drawings, and design adapters or local modifications.
Install any temporary stays or load-transfer devices, then de-tension the old cable gradually (cutting strands one at a time or releasing the anchorage with a jack), monitoring deck level and adjacent cable forces.
Remove the old cable in sections and install the new one, strand by strand for parallel strand stays or as a prefabricated hanger with sockets, stressing to the target force from the stage analysis.
Repeat in the planned sequence, usually alternating sides and spans to keep the pylon and deck balanced, and re-tune forces across the whole cable set at the end.
Fit dampers, anchorage protection and sheathing, measure final forces and geometry, and set up inspection and monitoring for the new system.

Key numbers

Stagingusually one cable or one symmetrical pair out at a time, with lanes closed or loads restricted
Design loss-of-cable case (PTI DC45.1)any one stay removed for replacement under reduced live load; sudden loss checked with a dynamic factor of 2.0 on the static effect
Replacement stays15.7 mm seven-wire strands of 1,860 MPa, galvanised, waxed and individually sheathed, commonly 20–100 or more per stay
Programmea few days to two weeks per stay; 50–100 stays in one to three years
Indicative costabout USD 0.3–1 million per stay on major bridges

Where it fits

Cable-stayed bridges with first-generation stays (grouted strands in steel or PE pipes, early locked coil ropes).
Suspension and arch bridges with corroded or fatigue-cracked hangers and sockets.
Stays damaged by fire, vehicle impact or vibration.

Where it does not

Removing a cable whose loss case has not been checked.
Ordering new cable systems before measuring the actual anchorage geometry.
Working without wind and traffic limits for each stage.

Choosing it

Choose full replacement over repair when wire breaks are spread along the cable, water has entered through failed grout or sheathing throughout, or the cable cannot be inspected; repair or re-sheath when damage is local and the steel is sound.
Choose parallel strand replacement stays over prefabricated cables where access is limited and no large crane can reach the anchorages; they go in strand by strand and can be inspected and replaced individually later.
Provide temporary stays or deck support when the loss of one cable overstresses the deck or its neighbours; otherwise replace one cable at a time under traffic restrictions.
Replace all hangers of an arch or suspension bridge in one programme once one has failed from corrosion or fatigue; the others are usually close behind.

Plant, pace and money

PlantMonostrand and multistrand jacks, strand cutters, winches, temporary stay assemblies, cranes or deck gantries, access platforms on pylons, force and geometry monitoring.

ProductivityIndicative: from a few days to two weeks per stay once the cycle is established; a whole bridge in one to three years.

CostIndicative: of the order of USD 0.3–1 million per stay on major cable-stayed bridges including engineering and traffic management; hangers cost less per unit, and the programme cost is driven by access and closures.

Risks and controls

What goes wrong

Sudden release of stored energy when a loaded cable is cut.
Overstress of the pylon or deck if the sequence is wrong.
New anchorages not fitting the old anchor boxes.
Falling objects onto traffic and navigation.
Collapse when temporary support of the cable system is inadequate.

Quality assurance

Stage-by-stage force and geometry records against the analysis, system qualification tests (fib Bulletin 30, PTI DC45.1), force records per strand, anchorage protection inspection, final force survey by lift-off or vibration.

Origins

Many stays of the 1960s–80s (locked coil ropes, grouted parallel wires or strands in steel or PE pipes) showed corrosion or fatigue within decades, and several bridges had them replaced. Strand-by-strand systems with individually protected strands, which spread from the 1980s, were designed so that any strand or stay can be replaced; hanger replacement on suspension and arch bridges is older practice.

Examples

Stay replacement on 1970s and 1980s cable-stayed bridges with grouted stays, and hanger replacement on suspension and arch bridges whose hangers corroded or cracked at the sockets.

Case studies

Hale Boggs Memorial Bridge, LulingUSA · completed 2012All 72 stays of the 1983 cable-stayed crossing of the Mississippi were replaced one at a time. The new strand system did not fit the steel pylon anchorages, so the pylons had to be modified, adding about two years and USD 19 million in change orders.

Bridge of the AmericasPanama · 2009All suspender hangers of the 1962 steel arch bridge were replaced with parallel strand hangers after a 2005 inspection found corrosion in about 60 % of the wires.

Severn BridgeUK · 1985–91The strengthening and refurbishment programme for heavier traffic included replacing the original inclined hangers, which had suffered fatigue damage at their end fittings.