A detailed inspection of the Severn Bridge’s cable is to begin, following the discovery of corrosion on the Forth crossing.
Both the Forth, which opened in 1964, and the M48 Severn Bridge, which opened two years later, were designed by the world-renowned team Freeman, Fox and Partners. Earlier this year, the Forth was found to have cracks in the paintwork on the cables which had let in water, causing corrosion (Surveyor, 16 February).
Following the discovery, the ~Highways Agency~ ordered tests to be carried out on the Severn, because of the similarities of the designs.
The HA thinks it is likely that the 1,597m-long suspension bridge will – like the Forth bridge – have corrosion in its cables after 40 years of exposure to the elements. The tests will discover the degree of the damage.
If, as suspected, the tests reveal signs of wear and tear, expensive dehumidifying equipment will have to brought in to try and rectify the problem.
C Spencer which found the corrosion on the Forth, has won the contract to carry out the work on the Severn.
The cost of dehumidifying the Forth is estimated at around £12M. However, the Severn could cost as much as £20M for the same process, according to ~Highways Agency~ structures team leader, Martin Lynch.
He said: ‘Given the finding on the Forth, it would be remiss not to fully examine the Severn. Everything we get back is a result, but we may not find any corrosion until the last stages of the tests.’ He also stressed most of the work – due to start next month – would go on at night and, although the team would need to close eight lanes over the four-month project, he said there was no reason why this would adversely affect traffic flows on the bridge.
Lynch also said the management of the Humber Bridge, where Freeman, Fox and Partners was consulting engineer, was also investigating the costs of buying dehumidifying equipment as a ‘preventative’ measure.
The bridge, opened in 1981, is two decades younger than the Forth and Severn, so is not expected to be suffering from corrosion at this stage.