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The same team that worked on the Forth Road Bridge cable
inspections in 2004 has been appointed to install state of the art
dehumidification equipment on the main cables of the bridge. The Forth Estuary
Transport Authority (FETA) has approved the appointment of C Spencer Ltd to
carry out the work. Bennett Associates will be working alongside C Spencer Ltd
on the £7.8m contract.
C Spencer and Bennett Associates were involved in the unwrapping
and original internal investigation of the cables of the Forth Road Bridge in
2004. The inspection revealed that the cables had suffered significant
corrosion; the current loss of strength, as verified by a Scottish
Executive-commissioned independent audit, is believed to be in the region of 8
to 10 percent. The discovery of corrosion in older suspension bridges in the USA
prompted FETA to become the first European bridge authority to carry out an
internal cable inspection.
A package of measures was put in place by FETA to monitor the
corrosion and minimise further deterioration. Dehumidification was quickly
identified as the best line of defence against further corrosion.
C Spencer, working in collaboration with Bennett Associates, will
install equipment that will inject dry air into the main two cables of the Forth
Road Bridge . Dehumidification works on the principle that if the relative
humidity of the air within the cable is reduced to 40 percent, then corrosion
cannot occur.
This particular method is already used in Japan and Sweden where
dehumidification systems are fitted to newer bridges as a preventative measure.
However, this is the first time that a dehumidification system will be
retrofitted in an attempt to stop ongoing deterioration of the cable.
Bennett Associates have designed two 30m long steel gantries that
are traveling along each of the main cables up to the top of the towers some
100m above bridge deck level. The temporary gantries allow access so that work
can be carried out sealing the main cables along their full length, and
installing air injection and exhaust points.
Sensors are mounted at regular locations along the main cables to
monitor the condition of the air as it passes through. Bennett Associates have
designed a bespoke software system for recording and presenting the data and
allowing secure access and process control from any internet connection
worldwide.
Based in Rotherham, South Yorkshire, Bennett Associates is a
leading engineering solutions provider with expertise in tunnelling machinery,
pipelines, vessels, movable bridge structures, aerospace, oil & gas and nuclear
applications. Their projects include involvement in the Airbus A380
'super-jumbo', the Falkirk Wheel Boat Lift, the Gateshead Millennium Bridge and
the Channel Tunnel. For more information, contact us on
01709-373782
February 2007
Related links:
 Innovative
Solutions for First Forth Bridge Inspection
Bridging
Gaps
M G Bennett and Associates Ltd is now part of the  Group |
