18 | the rail engineer | november 2012
feature
writer
David Shirres rail route between Edinburgh T heanddirect Dundee required the construction
(Below) Aerial view of Tay Bridge from the South. (Inset) View of bridge from Wormit shore.
of the Forth and Tay bridges - respectively the UK’s most iconic and longest. This was a massive investment and demonstrated the economic importance of rail traffic of the time. However, it didn’t start well. The first Tay Bridge, which opened in 1878, was designed by Thomas Bouch and took six years to build. Eighteen months later, it collapsed in high winds as a train crossed over it, killing 76 people. At the time, Bouch had started to supervise construction of a Forth rail suspension bridge. Not surprisingly this work was stopped. Following the disaster, the Board of Trade set up a commission to consider wind loading on railway bridges and Parliament specified that the Forth Bridge should “gain the confidence of the public and enjoy a reputation of being not only the biggest and strongest, but also the stiffest in the world”. Another grim consequence of the bridge’s collapse was a poem about the disaster by William McGonagall, arguably Britain’s worst poet.
The longest bridge Work on the current Tay Bridge started in 1883 and took five years. The contractor was William Arrol & Co, which also constructed the Forth Bridge. The Board of Trade specified that, for river navigation, the new bridge piers had to be constructed adjacent to those of the original bridge enabling reuse of girders from the original bridge. Constructing the UK’s longest rail bridge required 25,000 tons of iron and steel, 70,000 tons of concrete, ten million bricks and three million rivets. The bridge is 10,711 feet long and has 85 piers. The south approach from Wormit consists of piers 1 to 28 supporting lattice girders that carry the railway. Piers 28 to 41 are the “high girders” with the railway inside them to give shipping a 77 ft clearance at high water. The north approach from Dundee has piers 41 to 85. From Wormit the gradient falls at 1 in 762
Painting
over the south approach, is level through the high girders and then falls at 1 in 113 on the north approach down to Dundee. The Tay and Forth Bridges are impressive examples of Victorian engineering that have been inherited by Network Rail which now faces the challenge of maintaining these huge structures in a harsh marine environment. With the completion of the £130 million repainting project last December; this is not such an issue for the Forth Bridge. However there is still much to be done on the Tay Bridge. the rail engineer was invited to the middle of the Firth of Tay to learn more.
Painting is the easy bit Stuart MacDonald is a man who has given a lot of thought to his task of painting Britain’s longest bridge, commenting: “It’s all about logistics, painting is the easy bit”. Stuart has been on the bridge since June this year and is project manager for Taziker Industrial (TI) which has been awarded a two year £15 million contract for phase three of Network Rail’s Tay Bridge refurbishment programme. This comprises piers and spans 12 to 27 (immediately south of the high girders) and 80 to 83 (landspans at the north end of bridge). Network Rail’s construction manager, Ian Simms, has worked on the bridge in various capacities for 20 years. He advises that TI’s contract is part of a long term four phase programme that started in 2006 and is planned for completion in 2017 the final phase being the high girders.
the Tay
As well as painting, TI’s contract requires them to repair steelwork defects before applying the surface treatment. Experience to date is that there are typically 240 such defects per span. Most of these are minor repairs requiring small amounts of steel for which TI have a fabrication shop in their compound on the north side of the bridge. To do this work, TI has a workforce of more than 55 employees, including those from Network Scaffolding, a division of TI. Ten personnel alone are required for loading materials onto the bridge. The quantities of materials involved illustrate the challenge TI faces. Each span has 1200 square metres of steelwork and two 25 kg bags of grit are required to blast each square metre. The surface coating system is the same as that used on the Forth Bridge. This is a four coat treatment that requires a primer (5 square metres per litre); glass flake coat (1 square metre per litre); an intermediate coat (10 square metres per litre) and a final coat of Tay Bridge Grey (5 square metres per litre). Add to this the scaffolding and other materials required and the logistical challenge of getting these materials onto the bridge 1000 feet from the shore can be appreciated. One advantage is that, for phase three, there is no requirement for possessions to work on the steelwork below the railway or to access it. Night-time possessions are however required (4.5 hours on weekdays, 6 hours on Saturdays) to transport materials onto the bridge from TI’s storage compound