The recent news reports on the new bridge over the River Forth in Scotland are a testament once again to some stunning innovations in welding. The Queensferry Crossing stands alongside the much-admired road and rail bridges, providing a fast route for 24 million vehicles, starting in September 2017. At 1.7 miles (2.7 km) long, it is now the longest three-tower, cable-stayed bridge in the world. Not only that, but its shimmering cables make a majestic silhouette that is more than a match for the other two major bridges in this busy corner of Scotland.
Installing the deck segments was a tricky operation
One of the most delicate parts of the bridge’s construction was the installation of 110 standard deck segments made of reinforced concrete and weighing 750 tonnes each, plus 24 starter and approach segments. These were manufactured in China, fitted on the dockside at Rosyth, and then transported by barge to the towers. Deck height was about 55 metres from sea level, and the foundations were dug to a depth of 20 metres under the sea. Over 23,000 miles of cabling were used, making this this truly one of the most challenging construction projects ever seen in the UK. Once the deck segments were lifted into place, they had to be attached to their neighbours by means of a perfect weld and reinforced concrete “stitch”, with some final bolts as well. Work had to be halted several times, because of adverse weather conditions that made these crucial steps impossible to complete within the exacting tolerances required. Despite these drawbacks, the project was finally finished in the summer of 2017, and the magnificent bridge was officially opened by the Queen on the 4th September.
New design with innovative wind shield protection.
There were some major issues with the existing Forth Road Bridge, including frequent closures due to the extreme wind conditions in the Firth of Forth, and some well-publicised urgent repairs using a welded stiffening plate and jacking solution at the faulty truss end link locations. The new bridge has built-in wind protection in the form of 3.3 m. high shields, to allow a maximum speed of 70 mph for traffic in six lanes. Theoretically, these shields should be able to protect traffic from wind speeds of up to 184 km/h.
Improved access for maintenance teams.
Lessons have been learned from the recent work on the older Forth Road Bridge. Most of the internal structure of the new bridge is underneath the main carriageway, and maintenance workers will gain access to this enclosed space via a two-person monorail. This will be a lot safer and more comfortable than the harsh conditions that were endured by the welders who worked on the construction of the bridge itself. Anything that cuts down the time that welders need to spend on simply getting to the job can only be good.
Beautiful and built to last.
It remains to be seen how well the new bridge stands up to the heavy traffic and unforgiving weather of the far north, but for the time being, there is no doubt that this major infrastructure project represents a significant milestone in welding history. Now there are three fantastic monuments to the skill and dedication of welders, spanning the same stretch of the mighty Forth, one from each of the last three centuries. The graceful peaks formed by the towers and cables of Queensferry Crossing are set to capture the imagination of locals and visitors alike. They reflect the achievement of the latest generation of architects, builders, welders, project managers and other technical experts, all of whom should be very proud of their contribution to British engineering history this year.