A £2.6 million contract is to be awarded to C Spencer Ltd to carry out a third internal inspection of the main cables on the Forth Road Bridge.
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 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.
C Spencer Ltd have been appointed to carry out the work following a competitive tendering exercise.