It is the longest of its type in the world, the UK’s tallest and an engineering record breaker.
The £1.35 billion Queensferry Crossing will become Scotland’s latest marvel today when it opens for traffic to replace the Forth Road Bridge between Fife and Edinburgh.
The epic construction project was ordered by ministers a decade ago and has taken six years to complete. It has also taken shape amidst some of Scotland’s worst weather in the often hostile conditions of the Queensferry Passage.
When it was planned, an entire extra year was added to the project to allow for bad weather – that’s some 25 per cent downtime.
But in the end, even that proved an optimistic underestimate, with some 35 per cent lost to high winds and other adverse conditions – and the bridge will open eight months later than scheduled as a result.
Project technical director Mike Glover said the location had presented a formidable challenge to workers.
He said the fetch [length of water over which wind has travelled] stretches back to Falkirk, giving the wind “time to sort itself out. We have experienced some tremendous wind effects.
“It has taken some courage to work at up to 207m (700ft) above the Forth – we have relied on the resilience of the workforce to do it.”
What they have produced is, at 1.7 miles, the longest three-tower, cable stayed bridge in the world, and the highest in the UK – 50m above its elder sister. The Humber Bridge’s 162m towers were the previous highest.
Records have included the world’s longest continuous underwater concrete pour, into the Statue of Liberty-height foundations of the south tower over 15 days in 2013.
For a short time, a nearly half-mile-long deck section built out from the centre tower became the longest of its type anywhere.
The feats were achieved by the Forth Crossing Bridge Constructors consortium, one of two which had bid for the £790 million principal contract, which comprised Spanish firm Dragados, Hochtief of Germany, American Bridge International, with Scottish company Morrison Construction.
Building started in summer 2011 with excavation of the river bed down to rock for the north and south towers. The top 4.5m of Beamer Rock – only about 1m of which was above the water – was blasted away for the centre tower to rest on.
Huge steel caissons, 30m deep, were sunk to become the tower foundations by pumping in water and concrete,
The concrete towers were built in 4m sections, with the giant cranes involved rising to 235m by the time they reached their full height.
The deck which carries the road was then built out from the towers, in 122 sections, much of it from China.
The bridge’s approach viaducts – between the shore and outer towers – were pushed into place from either end, in a similar way to Clackmannanshire Bridge, the next up river.
A total of 288 cables support the deck, each containing up to 109 strands of steel wire, threaded through white pipes.
The bridge will have two lanes in each direction like the Forth Road Bridge because of ministers’ decision not to increase its vehicle capacity.
However, is likely to be less congested than the Forth Road Bridge – unless it attracts more traffic – by having a hard shoulder. It will also become a motorway by early November, with a 70mph speed limit compared to the current bridge’s 40mph.
Windshielding means it should virtually never have to close. The 3m high screens will reduce the wind effect to that of the rest of the road network.
But, as Scotland on Sunday revealed at the weekend, the Scottish Government has admitted that the hard shoulder could be used in the future, should congestion increase, such as for cars carrying passengers.
Eleven years ago, Riccardo Marini, then Edinburgh City Council’s city design leader, told The Scotsman that the new bridge should “make your heart soar” and would be “an incredibly important visual statement for the nation”.
Reflecting on the finished product this week, he said: “is this bridge beautiful? Beauty is in the eye of the beholder. I believe the design solution and the aesthetic impact it creates is a positive one.”
However, he added: “We are addicted to the internal combustion engine. It is killing us in so many ways, so my opinion of the bridge is tempered by the desire to scream: Stop making it easy for cars to dominate our world.”