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Contractors World - UK & Ireland Vol 2 No 8
points, and reinforced concrete
corbels added to the sides of the
piers to accommodate the jacks,
an alteration for which listed
building consent was granted.
Concrete repairs were carried
out on the piers and a system of
cathodic protection installed.
It was always expected that
these bearings would need to be replaced after a few decades. Similar replacements have been carried out on
viaducts all over the world, most recently in Scotland on the Tay Bridge. Like all moving parts, the bearings will
eventually wear out, so it’s important that they are replaced now before they present any safety risk.
Balfour Beatty Civil Engineering have been contracted to carry out the works under the supervision of consulting
engineers Atkins, following a competitive tender process involving six potential contractors. Balfour Beatty scored
highly for quality and bid £13.6 million to carry out the works.
Bridge begins to show its age
A total of 28 nuts on the bolt assemblies have now been found to have cracked and the need for replacement is
sufficiently urgent that the ‘negotiated procedure’ is to be used, as set out under EU procurement directives. This
means the bridge authority would negotiate a contract
directly with a preferred supplier rather than putting a
contract out to tender. The time saved would allow work
to begin before the onset of winter this year rather than
next spring.
Concerns about the cable band bolt assemblies were
first raised in 2007 when bridge inspectors discovered a
number of cracked nuts on the ‘cable bands’ that hold
the vertical hanger ropes to the main suspension cables.
The cracked nuts were replaced and a sum of £530,000
was set aside to replace all of the nuts over time using in-
house labour.
However, inspections this year have revealed a further
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cracked nuts, including three cable bands where nuts
on two bolts have cracked. Emergency repairs have been scheduled
and the most critical location has already been repaired. Further
replacement of faulty bolt assemblies will be carried out over the next few weeks.
Engineers have now concluded that all of the cable band bolt assemblies should be redesigned and replaced as a
matter of urgency.
The cost of redesigning and replacing all of the cable band bolts as well as the nuts has been estimated at £5
million. Transport Scotland will provide £4.15 million and the remainder will be met from FETA’s reserves or by
rescheduling other work.
Work on the replacement design will need to be completed before new nuts and bolts can be manufactured and
work can begin on site.
Barry Colford, Chief Engineer & Bridgemaster, said: “Thanks to the diligence of our bridge inspectors we are
identifying these cracks soon after they occur and are able to respond quickly to implement any repairs that are
required.
Until we have replaced all of these bolt assemblies, it is quite possible that further emergency repairs will have
to be carried out at short notice, requiring weekend traffic restrictions.
So far we have been able to limit the disruption this has caused, but this would become increasingly difficult
if failures occur during the winter when light and fair weather are in shorter supply. That’s why it’s critical that we
replace the bolts on the worst affected areas this autumn.
[
CWMAGS]
Concerns about the cable band bolt assemblies
were first raised in 2007
Europe’s longest suspension bridge when
it opened in 1964, the Forth Road bridge
is now beginning to show its age.