Amar Bahra helped engineer a striking new bicycle and pedestrian bridge over the harbour in Copenhagen. Here he discusses his work on the project, which has been shortlisted for The Structural Awards 2017.
Since opening in July 2016, the Inderhavnsbroen (known as “the Kissing Bridge” due to its opening mechanism, where the two moving spans kiss at the centre) has dramatically reduced commuting time for tens of thousands of pedestrians and cyclists per day in the Danish capital.
There is no other bridge like this anywhere in the world, largely due to its form and operation.
The geometries of the steel moving spans are highly unusual. The conventional rules for steel box girder bridges did not readily apply to all aspects of the design, requiring us to apply first principles and enabling us to achieve some architecturally stunning forms in the steelwork.
The bridge is 250m long, comprising the two central moving steel box girder sections (carrying a 3m pedestrian and 4m cycle path) and two pairs of concrete box girders (two carrying a 4m wide pedestrian path to the south and the other two a 4m wide cycle path to the north). The navigation channel is 45m wide, and the 70m main span of the structure is comprised of the two cantilevering steel spans, each weighing 230 tonnes, and which are joined at the centre with two tapering nose pins that engage in flared sockets as the spans move together.
Each moving span is supported on a pair of 1.8m diameter forged rollers resting on the main Y-shaped channel piers and bearing against a track incorporated into the soffit of the steel span. The rear of each moving span is supported by pairs of bogies running on stainless steel tracks set into the sides of the pairs of parallel fixed concrete approach spans. As the moving spans roll back to open the bridge, the rear bogies move away from the front roller support, changing the moving spans from cantilevers to simply-supported girders.
Simplicity and modesty can be engineering achievements just as much as innovative forms and bold statements. I would like to think we achieved both with the Inner Harbour Bridge: it is an understated, subtle structure designed to last a century, whose low-lying form keeps harbour views uninterrupted.
The bridge actually enhances visitors’ experience, providing a new meeting place over the water that boasts a unique, almost silent opening mechanism that has become an attraction in its own right, showcasing engineering to the public.
(Image: Jasper Carlberg)
One of the positive lessons learnt that could be taken forward is that with this structural arrangement the bridge users can be part of the bridge opening and stand right next to the passing vessels – it is a unique interactive experience.
We’re excited to have been shortlisted for The Structural Awards 2017 – it’s exciting to compete against so much excellent structural engineering.
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