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Leonardo's small wonder in bridge design
June 2004
Is this bridge "art" or is it engineering? In fact it is both - although when Leonardo da Vinci first conceived the design in 1502 he had not meant it as a footbridge. His idea was for a colossal structure across Istanbul's fresh water estuary, the Golden Horn, to link Europe with Asia.
It was also Leonardo's intention to build the bridge in stone. Norwegian artist, Vebjorn Sand, has considerably scaled down the original concept and persuaded the Norwegian Public Roads Administration to build the footbridge in glued laminated timber 20km from Oslo. But the project has not been without compromise.
The Norwegian Public Roads Administration openly admits it has had to bend the rules to construct its Leonardo da Vinci footbridge. Under Norway's building standards, new bridges are supposed to have a service life of 100 years - even if, like the footbridge, they are made from timber. But according to the administration, the best service life estimate for this laminated timber bridge is just 40 years.
"An exception from the design rules was given on this point on artistic and aesthetic grounds," says the administration's Tormod Dyken. Writing in the administration's research journal, Mr Dyken says that had the bridge been given extra weather protection with metal cladding or plastic coating, its artistic beauty would have been harmed.
"It is neither an engineer's bridge nor the most efficient way of bridging a highway, but it serves its function, provides the road-users with a beautiful sight, the municipality with a sculpture and pedestrians and bikers passing over the bridge with an experience," he says.
"Last, but not least, the unusual and beautifully shaped bridge may lead to increased public interest for bridges in general."
Meanwhile there is still much speculation to be had about Leonardo's original design. If the bridge had actually been built across the Golden Horn in 1502, it might not have lasted as long as the planned life of Norway's version.
In 1509 an earthquake destroyed much of Istanbul and the bridge would have been at the centre of it.
But engineers from the Norwegian Public Roads Administration believe that although Leonardo was pushing the limits of 16th Century technology, his stone bridge with its 234 metre free span, could have been constructed. At the time the largest stone bridge span was 37.5 metres. Even today, the largest stone bridge in the world, the Wuchao River Bridge (1990) in China's Hunan Province, only spans 120 metres. Leonardo's bridge towering 70 metres above the Horn would have rated as a wonder of the world.
