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Three Centuries of Bridge Building in Scotland

June 11, 2020
The three bridges over the Firth of Forth (from left to right); the Forth Bridge, the Forth Road Bridge, and the Queensferry Crossing.
The three bridges over the Firth of Forth (from left to right); the Forth Bridge, the Forth Road Bridge, and the Queensferry Crossing.

It’s impossible to ignore the infrastructure of the landscape in central Scotland at the Firth of Forth estuary, which reaches about 50 feet inland. Three bridges span the immediate vicinity of each other. The Forth Bridge, a steel bridge from 1890, serving rail traffic, while the Forth Road Bridge, a suspension bridge built in 1964, is now used exclusively for bus, bicycle, and pedestrian traffic.

The new bridge, called the Queensferry Crossing, supplements these existing structures. It is used for road traffic alone, with two lanes and an additional hard shoulder in each direction. Towering over 656 feet in height, it is one of the largest infrastructure projects in Europe.

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 Queensferry Crossing is one of the largest infrastructure projects in Europe.
The Queensferry Crossing is one of the largest infrastructure projects in Europe.

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.

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