By Aileen Robertson

JAPANESE ENGINEERS visited the Forth Road Bridge yesterday in a bid to prolong the life of the 42-year-old structure.

Bridge operator Forth Estuary Transport Authority (FETA) has warned corrosion within the main cables could lead to the crossing being closed to heavy lorries in 2013, and shut altogether in 2019.

FETA plans to invest £12 million in a dehumidification system which would dry out the insides of the cables and, hopefully, slow down the bridge’s deterioration.

However, the bridge authority still maintains a second bridge will need to be built.

The engineers from Japanese firm Nippon Steel are part of an international team commissioned by FETA to come up with a solution to the corrosion. Engineering consultant Faber Maunsell is leading the project.

Nippon Steel has designed and installed dehumidification systems for Japanese suspension bridges including the Akashi Kaikyo, or Pearl Bridge, which has the longest bridge-span in the world. If given the green light, the dehumidification equipment would be fitted to the west cable next year while the northbound carriageway is closed for resurfacing work.

While the equipment has been fitted during the construction of suspension bridges in Japan as a preventative measure, it is not known if it can halt corrosion that has already started.

FETA has said it could be five years before it is known if the system has worked, but depute general manager Barry Colford said he was confident the investment would be worthwhile.

“We’re optimistic that this system will stop the corrosion, but there are no guarantees,” he said.

“FETA is delighted to have recruited a team of international experts to design a dehumidification system for the Forth Road Bridge’s main cables.

“This is obviously quite a specialised area of expertise, which is why our consulting engineers Faber Maunsell have assembled some of the best engineering talent from Japan, the USA and the UK. Included in the team are engineers from Nippon Steel, the Japanese company that developed this technology.

“We’re now working through the technical details involved in designing the system, with a view to starting work on installing it next year. We’ll fit dehumidification to the west cable in 2007, then the east cable in 2008, after which the system will be fully operational.

“Some traffic restrictions will be required during installation, but we’re hoping to minimise the amount of disruption caused by doing this at the same time we resurface the northbound carriageway.”

An inspection of the bridge’s main cable in 2004 showed that in one section 31 wires had broken as a result of corrosion. However, the broken wires represented less than 0.3% of the total and bridgemaster Alastair Andrew said there was no cause for bridge users to be concerned.

An inspection of the Severn Bridge’s cables ordered following the report found that the crossing near Bristol was in a worse state than the Forth Road Bridge and traffic restrictions may have to be imposed by the end of the year.