Extending the life of the main cables of two major UK suspension bridges through dehumidification

Abstract

The 1960s saw the construction of two major suspension bridges in the UK. With a span of 1006 m, the Forth Road Bridge was a traditional design, whereas the M48 Severn Bridge at 988 m span was a highly innovative design using a steel box deck for stiffening. After nearly 40 years of heavy use the owners of Forth Road Bridge decided to carry out an internal inspection of their cables, which revealed unexpected results of corrosion, broken wires and a loss of strength. A review of how these problems were addressed and solved around the world was undertaken and cable dehumidification was seen as the best option. Installation of the Forth dehumidification system is nearing completion and sets new standards in terms of its method of installation, efficiency, and web-based control system. An inspection of the Severn Bridge cables followed the Forth inspections and somewhat worse results were revealed, which prompted the need to urgently install a cable dehumidification system. A partial system was rapidly designed and installed on the most deteriorated sections of the main cables, followed by a full system on the remainder of the cables. The full system is now commissioned and operating.

Economic impact of bridge functionality loss from a resilience perspective: Queensferry Crossing, UK

“…In 2008 a second inspection indicated an increased strength loss to 10%. Acoustic monitoring systems were fitted on the cables to detect the rate of future wire breaks and dehumidification systems were fitted to stop or slow down the rate of deterioration (Cocksedge and Bulmer, 2009).…”