Contractor C Spencer has been awarded a £2.6M contract for a third internal inspection of the main cables on the Forth Road Bridge.
The 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 carefully chosen locations. Hardwood wedges will be driven into the bundles of wires, allowing engineers to see right into the centre and assess the condition of a representative sample. The condition of the wires will be recorded and samples taken for laboratory testing.
Similar inspections were carried out in 2004 and 2008, when significant corrosion was discovered in the 11,618 high tensile steel wires that make 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 contractor was appointed to carry out the work following a competitive tendering exercise, but 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, bridge authority Feta entered into negotiations with the contractor to reduce the price to an affordable level. The overall extent of the inspection has since been reduced. Consultant Flint & Neill had already been appointed to oversee the inspection on behalf of the bridge authority.