New long span bridge designs that could ultimately cover distances such as the Strait of Gibraltar, connecting Europe and Africa, could be made possible by UK research.
In an EPSRC-funded project, researchers at Sheffield University and Brunel University London, alongside long span bridge expert Ian Firth of engineering consultants COWI, used a mathematical modelling technique to identify new bridge forms.
Most existing long span bridges are either suspension bridges, such as the Humber Bridge, or cable-stay, such as the Queensferry Crossing.
However, as these bridge spans increase in length, more and more of their structure is needed just to carry their own weight, according to project leader Prof Matthew Gilbert at Sheffield University.
“There is a theoretical limit on how long a bridge span can be before the material fails,” said Gilbert.
So instead the researchers set out to investigate whether new designs could lead to more structurally efficient forms, allowing longer bridge spans to be built.
The researchers developed a mathematical optimisation model, in which they incorporated a nineteenth century mathematical theory by Davies Gilbert, who advised Thomas Telford on the design for the Menai Suspension Bridge in North Wales.
They found that the most mathematically optimal designs would contain regions resembling a bicycle wheel, with multiple spokes in place of a single tower.
However, since this would be difficult to replicate on a large scale, the team replaced these wheels with simpler split towers comprising just two or three spokes each.
“Very often there are slight variations on [the mathematically optimal] forms, which are only very slightly less efficient, in that there is very little extra weight, but they are much easier to build,” said Gilbert.
In the design, the forces from the deck are transmitted more efficiently through the bridge superstructure to the foundations, meaning less material is needed. This is done by keeping the load paths short, and avoiding sharp corners between tensile and compressive elements.
More work is needed to ensure the new designs are practical, including how easy they will be to construct, said Gilbert.
“We haven’t yet looked at the lateral loading from wind,” he said. “So we’d like to work with experts in that field, to see whether [the design] is a practical solution for very long spans.”
The research is published in the Proceedings of the Royal Society.
They should consider the Composite beam structures invented by John Hillman of HBC Inc of Chicago and U of Maine and using polymeric light weight Concrete/Cements. Beams can be constructed up to more than 125 feet long. Even they columns could be composites.
Look at the recent UK Acton Swing bridge repair using light weight concrete.
Thanks for the acknowledgment Geoff. Innovative solutions are often fostered by adjacent possibilities.
The answer to super long bridge weight is carbon fibre rods – ultra strong solid cables – but ultra costly.
Is there a sufficient economic justification for a bridge there?
Why? Is it purely an exercise in ‘because we can!’? If it ever got the go ahead it could be a magnet for terrorism. Right wing groups would say it will make the migrant problem worse. Spain would keep closing the border with Gibraltar every time there is a little dispute with the UK.
I think such a link would be a good idea, but why not a tunnel?
Since the rock beneath the Straits of Gibraltar is solid and would not leak water during the drilling of the tunnel, and since tunnels through tall mountains do not collapse under the pressure of weight of the rock of mountains over 1,000 ft tall above such tunnels, why can’t a tunnel through the narrowest part of the strait withstand the pressure of the 3,000 ft deep? Sure 3,000 ft is deeper than 1,000 ft, but rock is of course solid and dense.