Construction methods · Cable-supported and arch bridges

Cable wrapping and dehumidification

Main cables corrode from inside; the modern cure is to wrap them airtight and blow dry air through them at 40 % relative humidity. Applied on new bridges from the start and retrofitted on old ones, it has replaced red lead paste and re-wrapping as the way to keep a cable for a century.

How bridges get built · Cable-supported and arch bridges · Cable wrapping and dehumidification

Also called: main cable dehumidification, cable wrapping, cable corrosion protection

How it is done

Wrap the compacted cable with S-wire or an elastomeric wrap over a corrosion inhibitor; seal cable bands and saddles.
Install injection and exhaust sleeves along the cable, a dehumidification plant in the tower or anchorage, and sensors inside the cable.
Run the plant continuously; monitor humidity at the exhausts.

Where it fits

All new suspension bridges; retrofit on cables with wire breaks found in inspections; also stay anchorages and closed box girders.

Where it does not

Skipping the airtightness test; a leaking wrap wastes the plant.

Plant, pace and money

PlantWrapping machine, dehumidifiers, ducting, sensors.

ProductivityWeeks per cable.

CostUSD 1-5 million per bridge; small against cable replacement.

Risks and controls

What goes wrong

Wrap leaks at bands, plant failure unnoticed, condensation at cold spots.

Quality assurance

Pressure tests of the wrapped cable, humidity logs, periodic inspection.

Examples

Akashi Kaikyo (first), Great Belt, Humber retrofit, Forth Road Bridge retrofit, Yi Sun-sin.