Almost 2,000 heavy-duty nuts are to be replaced on the Forth Road Bridge in case they fail in the future, it was disclosed yesterday.
The move comes after bridge inspectors found nine cracked nuts during a routine check last year.
Bridge operators Forth Estuary Transport Authority (Feta) said the replacement of the 1,888 nuts is precautionary and the bridge remains safe.
The nuts are used to secure 192 “cable bands” to the bridge’s main cables.
Cable bands are metal castings over which the steel rope hangers holding up the roadway are looped.
Each cable band is held in place by a number of 35mm diameter steel bolts, pre-tensioned to a load of about 80 tonnes.
All the cable band nuts and bolts were replaced in the late 90s, but an inspection last year found nine nuts had cracked.
Feta then ordered an investigation, which involved work carried out by consulting engineers Faber Maunsell.
Now a report being sent to Feta’s board has concluded that 1,888 nuts, which are the same type as the nine that failed, should be replaced.
A Feta spokesman yesterday confirmed the nuts will be replaced. Disruption to traffic will be kept to a minimum, he said.
It is understood the work will be carried out over the course of the next few years.
The bridge authority’s investigation found design and specification decisions and construction methods may have contributed to the cracking.
The report found misalignment of washers may have led to uneven loading in the nuts and that the protective coating on the nuts may have allowed moisture to cause the damage.
The report states that Feta is seeking legal advice to find out if the designer or contractor who replaced the nuts in the 90s is liable.
Replacement of four failed nuts on the west cable, using access platforms already in place, has so far been completed. The five failed nuts on the east cable will be replaced in the course of this year.
Bridgemaster and chief engineer Barry Colford said: “Thanks to the vigilance of our inspection team, this problem was identified at an early stage and the bridge remains perfectly safe.
“Cracks have been found in only nine out of 1,888 similar nuts.
“Nevertheless, our investigation has concluded that any of these nuts could potentially fail in future, so the recommendation is to replace them all as a precaution.
“We’re planning to carry out further tests in the laboratory before bringing a final report to the Feta board later this year.”