When the Forth Road Bridge began to deteriorate and was threatened with closure, it was vital to keep the Edinburgh-Fife trunk road open for the tens of millions of journeys made each year. The solution was to build a new Queensferry Crossing bridge, at 1.7 miles long, it is the world’s longest three-towered cable-stayed bridge, Britain’s tallest bridge, and Scotland’s largest construction project in the 21st century. Since completion it has delivered huge benefits for the economy, businesses and local people.
The Queensferry Crossing was taken from inception to completion in just 10 years. Widely hailed as an all-around success, it broke engineering records while coming in 65% under its original budget. The bridge, designed by our the ALLPLAN customer Leonhardt, Andrä und Partner Beratende Ingenieure VBI AG, has received the Major Project Award at the Royal Academy of Engineering’s 2020 almost exactly three years after its official opening by Queen Elizabeth II.
Transport Scotland’s consultants from the Jacobs Arup joint venture were not given an easy task in developing a concept for the new bridge. It had to be an equal counterpart to the world cultural heritage of the Forth Bridge. The final design result was a cable-stayed bridge over a mile long with three pylons in the water. The middle pylon of the three pylons proved to be particularly challenging. In the case of traditional cable-stayed bridges, the center pylon is back-anchored via rigid side sections located at the edge.
However, this approach was not possible with a three-pylon bridge, due to the very high bending moments. Plus, it was very important that the new bridge did not appear excessively dominant in the context of the other two.
The planners achieved the back-anchoring of the central pylon by overlapping the stay cables by 479 feet in the middle of the respective section. The reinforcement of the individual pylon segments had to be placed precisely in the space due to the upward-tapering cross-section. This method placed high demands on the CAD software used. It was crucial that all team members were able to visualize the design with the greatest attention to detail. That is why planners from the firm LAP also relied on Allplan Engineering for the reinforcement and design planning. It was possible to meet deadlines and costs thanks to accurate, collision-free planning.
The Queensferry Crossing is the largest bridge for which 3D reinforcement planning was entirely created using Allplan Engineering.
Editor's Note: Scranton Gillette Communications and the SGC Infrastructure Group are not liable for the accuracy, efficacy and validity of the claims made in this piece. The views expressed in this content do not reflect the position of the Roads & Bridges' Editorial Team.