You could be forgiven for expecting a bridge to rise above the water over which it is intended to span. A new bridge in the Netherlands, however, takes a different approach. The Ravelijn Bridge floats on top of the water, providing access to and from the Ravelijn fortress-island.
Bridges aren't the only unusual objects that have been adapted to float. Earlier this year Gizmag featured a floating sauna that is planned for launch in Seattle and, more recently, a floating skateboard ramp has been installed on Lake Tahoe. London's Floating Cinema, meanwhile, has become an annual attraction.
One could reasonably argue that the Ravelijn Bridge is more of a walkway than a bridge, but it achieves its purpose of getting people across the water to the Ravelijn fortress nonetheless. What's more, it does so in a manner that is elegant and sympathetic to its surroundings.
The bridge was originally commissioned in order to connect the fortress to the city center and to provide a second route of exit in case of emergency. Rather than being straight, it snakes across the water following the route that rowing boats used to take when the fortress was still in use.
The structure is made of Accoya, a modified and treated wood that is said to be ideal for outdoor use and applications that require durability. It is resistant to fungal decay, as well as the effects of swelling and shrinkage that could otherwise result from its contact with water.
The Accoya decking is floated on the water using air-filled polyethylene pipes explains project architect Ad Kil to Gizmag. Sections for the bridge were prefabricated off-site and were transported to the location where they were assembled together.
Kil says that the biggest issues in creating the bridge were concerns about its convex shape and lack of railings. In order to allay those concerns and solve any problems that these features might have presented, a full-size part mock-up was created and tested.
The bridge is designed to be easily disassembled and recycled. This means is can be easily maintained and repaired should needs be. It can also be moved to the side of the water when it is not in use or should certain events so require, such as ice-skating around the fortress in the winter.
The Ravelijn floating bridge is 80 m (262 ft) in length and took 3 months to build. It was completed in March and is designed to last for at least 25 years.