31 October 2011
A US$4.2 million contract is to be awarded to C Spencer to carry out an internal inspection of the main cables on the Forth Road Bridge. The contract award follows negotiations and price-reduction measures as the tender had come in higher than expected.
Similar inspections were carried out in 2004 and 2008, when significant corrosion was discovered in the 11,618 high tensile steel wires that makes up each main cable, resulting in an estimated 10% loss of strength. A dehumidification system has since been installed in an attempt to dry out the cables and prevent further corrosion. This system has been fully operational since October 2009.
The third inspection, due to take place in 2012, will allow engineers to assess the current strength of the cables and gauge the effectiveness of the dehumidification system.
The main cables will be unwrapped at eight locations. Hardwood wedges will be driven into the bundles of wires, allowing engineers to assess the condition of a representative sample. The condition of the wires will be recorded and samples taken for laboratory testing.
C Spencer’s appointment follows a competitive tendering exercise. However, tender costs based on the initial specification came in higher than expected and the Scottish Government subsequently announced a 58% cut in the Forth Road Bridge’s capital budget over the next three years. As a result, the Forth Estuary Transport Authority (FETA) entered into direct negotiations with the contractor in order to reduce the price to an affordable level. Various cost-saving measures will be implemented and the overall extent of the inspection has been reduced.
Consulting engineer Flint & Neill Ltd have already been appointed to oversee the inspection on behalf of the bridge authority.
“The condition of the main cables is the second highest risk to the bridge after the condition of the main cable anchorages,” said chief engineer and bridgemaster Barry Colford. “We’ve already begun investigating the anchorages but this inspection of the main cables is also an essential project.
Work is expected to begin on site in spring 2012, although preliminary work will start immediately. The first results from the inspection should be available in early 2013.