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Last Updated: Saturday, 11 February 2006, 00:15 GMT
Study into Forth bridge dry-out
Forth Road Bridge
A study is set to find out if a drying system would work on the bridge
A study into the possibility of installing a drying-out system for suspension cables on the Forth Road Bridge is expected to get the go ahead.

It follows a report which warned the bridge could be shut to all traffic in under 14 years unless action was taken.

Consultants are to look into fitting 12m de-humidification equipment, which would pump dry air onto the wet cables.

The Forth Estuary Transport Association (Feta) is set to appoint engineers Faber Maunsell later this month.

Alastair Andrew, Feta general manager and bridgemaster, said a report into the matter would be discussed at the Feta board meeting on 24 February.

"The Forth Road Bridge has always enjoyed the very highest standards of safety and maintenance which are recognised across the world," he said.

"We are confident that by being pro-active in our investigations, following a very thorough and systematic approach to operational safety, we have caught the corrosion at a time when we can now do something about it.

Excellent track record

"The team Faber Maunsell has put together to carry out this study brings together the very best in experience across the world in dealing with similar situations.

"They have an excellent track record in understanding the complex issues involved in tackling corrosion in suspension bridges and, most importantly, providing the right solutions."

A detailed two-year internal inspection, completed by Feta in 2005, found evidence of corrosion inside the cables resulting in some reduction of cable strength.

Forth Road Bridge
The first phase of the study is likely to be complete by summer 2006

Experts say dehumidification is a "well-tried" system of preventing corrosion of galvanised steel, but its use on bridge cables is less common.

The proposal is to wrap the main cables in a neoprene membrane, then dry them out by pumping in dried air at various points.

The first phase of the study is likely to be complete by summer 2006, and will prepare the way for a tender to be awarded for contractors to install the dehumidification system by the end of the year.

Five years

Construction work, to be supervised by Faber Maunsell, could start as early as spring 2007, and will take around two years to complete.

Once the dehumidification system has been in place for five years, engineers will open up the cable to see if it has worked.

There is still a risk that, even after the equipment has been installed, corrosion might still exist in the main cables.

As well as exploring the feasibility of dehumidifying the cables, Feta has already committed to fitting acoustic monitoring, enabling the entire length of the cables to be monitored for any further wire breaks.

Work to install this equipment is expected to start on site as soon as April 2006.

Forth Road Bridge closure warning
17 Nov 05 |  Scotland
Probe into bridge cable corrosion
10 Nov 05 |  Scotland
Forth bridge project costs soar
24 Aug 05 |  Scotland
Forth bridge work completed early
07 Jun 05 |  Scotland

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