Today is a great day for followers of the wild and wacky world of the bridge design competition.
At last, the public can see Techniker and Spence Associates' design for the River Wear Crossing competition. Since they won in September 2005, their design has been kept strangely secret. Architect Stephen Spence has complained loudly about this supposed injustice, stating that "his plans had been checked by engineers and no problems had been found". The Happy Pontist commented on the kerfuffle in July.
The bridge, along with a watered-down version and more conventional option, is to go to public consultation in the next few weeks. However, images of the design have been revealed early in the Sunderland Echo and The Journal.
The iconic bridge design is simply amazing. Amazingly beautiful. And amazingly daft. You can instantly see how it would appeal to the marketing types at Sunderland Arc, the development body who promoted the original design competition. It's tall, it's curvy, it's spectacular: in particular, it would make an exciting logo for the city of Sunderland. Thrusting upwards. Dynamic. That sort of thing.
Matthew Wells, the structural designer, says that "the bridge was not a technically difficult or radically new structure". He certainly knows his stuff, as evidenced by his very readable book 30 Bridges. The local press claims it's a bit like the Erasmus Bridge in Holland, to back up the view that it's a proven design. But here's where the problems really begin. It's nothing like the Erasmus Bridge, or any other cable-stayed bridge I've ever seen. And it undoubtedly is both technically difficult and radically new.
For one thing, the twisty masts tilt towards the deck they are supposedly supporting. At Erasmus (and other expensive designs such as Calatrava's Alamillo Bridge and Sundial Bridge), they slope away from the deck, which helps to counterbalance the dead weight and traffic loads.
At Erasmus, there are cables which hold back the masts, restraining them against the enormous horizontal forces introduced by the main deck cables. In Sunderland, there are no such cables, and the tops of the masts aren't even tied together. The whole bridge is therefore held up by tall, pointly cantilevers. Which tilt towards the deck. Calling that amazing doesn't begin to capture the audacity of the concept! It's a bit like hanging the Brooklyn Bridge off the side of the Empire State Building.
The Sundial Bridge just about gets away with this sort of ambition by virtue of being a relatively lightly loaded footbridge. But the River Wear crossing will carry a multi-lane highway. To avoid vibration problems, or just the deck sagging into the river, those masts would have to be enormously strong, with huge quantities of steel and concrete pressed into service. As a bridge engineer, I personally find it very difficult to imagine.
Go back to the original competition and you'll find that the budget for the bridge was £43m, which worked out at about £4,000 per square metre of deck. In my view, there's absolutely no way a bridge of this scale and type could be built for that sum.
I look forward to reading other views. It's good that at last this design has been made public, opening an opportunity for debate, not just about the merits of this particular structure, but about the process by which it was developed (a design competition, judged in secret, and without an experienced large-span bridge engineer on the jury). I also wonder about the process going forward: judging from the Sunderland press, there are strong voices in favour of the design, not least from the leader of local government opposition, who we might assume to be relatively ignorant of structural engineering (or at least to have commented prior to actually seeing the design). It looks like local people will be asked to tell their elected leaders whether they prefer bread or circuses: low-cost versus spectacle.
No doubt the designers will continue to defend their proposal robustly. But amongst all the consideration of cost versus quality that will probably dominate discussions, I think it's important not to forget about risk. Whether it will stand up or not, for a given budget or otherwise, it's undoubtedly a very high-risk proposal. And Sunderland might be wise to look at recent examples from Glasgow and Stratford-upon-Avon for cases where high-risk competition-winning designs were dropped only after first wasting considerable sums of public money.