In early 2010 Freyssinet Makers, the Northern structural repair division of Freyssinet Ltd, was appointed by Balfour Beatty Civil Engineering to complete refurbishment works on the Forth Road Bridge. This included bridge bearing replacement, concrete repairs and the installation of an impressed current cathodic protection system to the north and south approach spans to the main structure.
The Forth Road Bridge is located in Scotland, connecting Fife and the north east of Scotland with capital city Edinburgh and the south. When the bridge was opened in 1964, it was the fourth longest in the world, and the longest outside the United States, with a main span of 1006 meters between the two towers. In total, the structure is over 2.5km long.
Maintenance to the Forth Road Bridge is ongoing and a large capital programme to strengthen the bridge is also continuing. In 2009 the Forth Estuary Transport Authority (FETA) embarked on a competitive tender process for the Viaduct Bridge Bearing Replacement project, estimated to total £15 million.
The contract is the biggest single contract awarded since the bridge opened. It has involved the replacement of all the mechanical bridge bearings on the Forth Road Bridge’s north and south approach viaducts, which sit at either end of the bridge on each shore, connecting the A90 and M90 with the main body of the suspension bridge. The steel bearings support the bridge deck and enable it to move as required by changes in temperature. The contract also required an extensive overview of the concrete pier condition in conjunction with concrete repair works and the installation of an impressed current CP system.
Freyssinet was chosen to design, supply and install the bridge bearings, and complete associated concrete repair and cathodic protection works on the structure, having demonstrated a successful track record with this type of work.
40No. permanent mechanical bearings were specially designed to BS 5400, and manufactured in Freyssinet Ltd’s factory in Telford in quality controlled conditions that exceed the requirements of BS EN ISO 9001.
Freyssinet also designed and supplied 35No. temporary support bearings and over 100No. hydraulic jacks to meet the requirements of the temporary support and restraint works. In addition Freyssibar, Freyssinet’s own high-tensile pre-stressing bars, was supplied and stressed to assemble and fix the longitudinal restraint frames onto the structure.
Freyssinet were responsible for all the hydraulic jacking and monitoring of the bridge deck to allow removal of the existing bridge bearings. The bridge bearing replacement work by Freyssinet considered also the careful coordination of hydrodemolition works, steel cutting and drilling, and heavy lifting and positioning techniques to all allow the careful and safe positioning of each bearing into an extremely restricted access gap.
The impressed current CP system utilised three anode systems; titanium mesh, titanium ribbon and discreet mixed metal oxide anodes. In addition, galvanic anodes were installed into repairs outside the impressed current zones.
Over 14,000m of titanium ribbon anode strip was installed into the concrete faces of the pier head cross beams and legs to form part of the CP system. Freyssinet introduced an innovative technique that utilised a special chase cut into the concrete using a remote operated wall saw. This cut up to 60m per day without exposing operatives to excessive hand arm vibration or concrete dust.
Corrosion Control Services (CCSL), a sister company of Freyssinet, were involved in the procurement of specialist materials and supplied the necessary specialist site supervision / technical commissioning as required by the contract
The Forth Road Bridge is a category ‘A’ listed structure and consent had to be granted for the works to be carried out. Selection of all repair materials and methods of placement were carefully considered in technical trials prior to the start of the works in order to meet the requirements of the consent.
Freyssinet’s Northern Area Manager, Paul Wood, says “Works have progressed well, and are projected to successfully complete in August 2012, on time and within budget.”