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New bridge form mooted for Europe-Africa crossing

Gilbert long span bridges

A recently identified bridge form could enable a crossing between Europe and Africa, according to a study by leading bridge experts.

Cowi engineer Ian Firth alongside experts from the University of Sheffield and Brunel University London claim that a new bridge form “could enable significantly longer bridge spans to be achieved in the future, potentially making a crossing over the Strait of Gibraltar, from the Iberian Peninsula to Morocco, feasible”.

Using a mathematical modelling technique to identify optimal forms for very long-span bridges, the study has identified bridge concepts which they claim require “the minimum possible volume of material”, potentially making significantly longer spans feasible.

The designs contain regions which resemble a bicycle wheel, with multiple “spokes” in place of a single tower. But as these would be very difficult to build in at large scale, the team designed split towers comprising just two or three “spokes” to make the structure easier to construct.

The study adds: “For a 5km span, which is likely to be required to build the 14km Strait of Gibraltar crossing, a traditional suspension bridge design would require far more material, making it at least 73 per cent heavier than the optimal design.

“In contrast, the proposed two- and three-spoke designs would be just 12 and 6 percent heavier, making them potentially much more economical to build.”

The new bridge forms require less material principally because the forces from the deck are transmitted more efficiently through the bridge superstructure to the foundations.

This is achieved by keeping the load paths short and avoiding sharp corners between tensile and compressive elements.

University of Sheffield professor Matthew Gilbert, who led the research, said: “The suspension bridge has been around for hundreds of years and while we’ve been able to build longer spans through incremental improvements, we’ve never stopped to look to see if it’s actually the best form to use.

“Our research has shown that more structurally efficient forms do exist, which might open the door to significantly longer bridge spans in the future.”

Cowi bridge expert Ian Firth added: “This is an interesting development in the search for greater material efficiency in the design of super-long span bridges.

“There is much more work to do, notably in devising effective and economic construction methods, but maybe one day we will see these new forms taking shape across some wide estuary or sea crossing.” 

A connection between Europe and Africa has long been mooted, with the latest plans for a £7bn tunnel connecting Europe to Africa put forward in May.

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