 Further tests need to be carried out on the bridge |
The manager of the Forth Road Bridge has recommended spending �2m to assess the state of the structure's main support cables. Alastair Andrew said consultants have suggested the fitting of an acoustic monitoring system of a type used on several similar bridges in the US.
Tests have been carried out at low level points in the structure.
Mr Andrew warned that possible traffic disruption could not be ruled out during tests on higher sections.
He stressed that each main cable on the bridge is made up of more than 11,600 high-tensile steel wires and he had no concerns about the safety of the bridge.
He said: "The worst section so far has 31 broken wires but you must remember that the main cable consists of over 11,600 of these wires.
"So the fact that we've found 31 broken wires is a lot less than one eighth of one per cent of the total so there is no need for concern as yet."
However, Mr Andrew said the US consultants employed to assess the bridge had not expected to see the level of corrosion discovered during the inspection of the 40-year-old structure.
The corrosion was more likely to be found in a bridge more than 60 years old.
He said: "We do seem to be experiencing an accelerated rate of corrosion in that main cable."
Mr Andrew said weather conditions could be a factor but more tests were being carried out.
 Alastair Andrew will submit a report to the transport authority |
The proposed listening facility is designed to assist in working out the extent and rate of deterioration and could be installed this summer.
Mr Andrew has called for �500,000 to be spent on the acoustic monitoring of the bridge and a total of �2m on the entire five-year assessment.
A report will go before the Forth Estuary Transport Authority (Feta) on 3 March.
Checks higher up the structure are due to start in April when weather conditions improve and this could lead to temporary carriageway closures.
Mr Andrew said: "I think major works will be required but it's difficult to say at this stage what these works will be.
"As previously reported to my board, we are going to open up the main cable near the tower top.
"That means men working up at 300ft above the carriageway on a specially designed steel platform.
"This platform cannot be safely erected in the hours of darkness so we're also advising the board that we will need some limited carriageway closures during the better weather."
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We do seem to be experiencing an accelerated rate of corrosion in that main cable
