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Main cable inspection findings due later this year

Published on 27 Feb 2012

The Forth Road Bridge’s Chief Engineer has cautioned against jumping to conclusions about the lifespan of the bridge’s corroded main cables before the results of the latest inspection are known.

Barry Colford said: “Press reports suggesting that new findings on the condition of the cable are available are misinformed.

“While we are confident that our work will prove successful, there are no new findings at this stage and we must wait until this year’s internal inspection of the main cables is complete before reaching any conclusions.

“We are monitoring dry air going into the cables and dry air coming out, which is encouraging, however we won’t know how extensive an effect this had had until we open up the cables and take a look inside.

“The good news is that the inspection is on schedule and work on site will begin as planned in April. Findings will be available later this year, which will hopefully give us further confidence about the cables’ condition.”

Corrosion in the main cables was discovered during the first internal inspection in 2004. A loss of strength of approximately 8-10% was calculated, which was subsequently confirmed by an independent audit and by a second inspection in 2008.

Engineers installed a dehumidification system in order to slow down or halt the deterioration, which has been blowing dry air through the cables since 2009.

Barry Colford continued: “Dehumidification is a proven technique for preventing corrosion in steel, however this is the first time that such a system has been retrofitted to the main cables of a suspension bridge with existing corrosion on this scale. This is why we cannot be sure of success.

“Even if we successfully halt the corrosion, this does not guarantee that the cables will not lose further strength. Damage already done to the wires inside the cables cannot be repaired and there is no way of telling how many cracks will lead to breaks in future.

“There will always be some uncertainty and the cables will need to be monitored and inspected for the remainder of their service life.”

Cllr Tony Martin, Convener of the Forth Estuary Transport Authority, added: “It is important that we allow the engineers to complete their investigations before judging whether the problem has been solved.

“We have an excellent team working to save the main cables and there’s no doubt that they have given themselves the best possible chance of success, but they have made clear all along that there are no guarantees with such pioneering work.

“We must also wait for the results of the ongoing investigation into the anchorages and take into account the increasingly disruptive weekday maintenance that will be required due to continuing wear and tear on the Forth Road Bridge before reaching any conclusions about its long-term viability as a standalone crossing.”

The Bridge:

Facts & Figures

Opened 1964, 2.5 km long, Main span 1006 metres
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  • No restrictions on bridge (19:13 BST 26/09/14)