As a country known for its waterways the Netherlands has a long bridge building tradition. From trees over brooks, the tracks through marshes and the first big wooden bridges built by the Roman legions we have moved in the 20th century from wood and stone to concrete and steel. Wooden bridges were in fact only still being built as constructions for light traffic, preferably using a wood type in a high sustainability category.
Tropical hardwood with a high sustainability category is becoming harder to find. Also, the nature of tropical hardwood is such that it can only be made into a lengthy structure by using bolt connections. It is therefore necessary to find alternatives.
On the initiative of the Blauwestad project organisers, InVra plus and architecture firm De Zwartehond designed a number of wooden bridges to be built in Blauwestad by the company Schaffitzel from Schwäbisch Hall. The idea behind these bridges is that they can be built with a long life expectancy by using wood with a low sustainability class by means of lamination and smart detailing. InVra plus, De Zwartehond and Schaffitzel have been working together since 2005. The result: a number of laminated pine bridges that are suitable for the (former) traffic categories 300 and 450. A bicycle bridge with a length of 72 metres was also built.
Two more bridges have been added since 2012. The special aspect of these bridges - a debut in the Netherlands - is that they are made of wooden beams connected to the concrete surface using the HBV method. The bridges have been given a very slender appearance with two wavy beams as the bearing structures. Together with the concrete surface these laminated elements form a T-beam. The concrete surface protrudes so far beyond the wooden beams that the corbelling forms a kind of awning and the wooden beam protects against the rain. In accordance with the current building standards this can be treated as a sheltered structure and is a good example of sustainable detailing with wood.
InVra plus has developed and built three VK 450 bridges together with Schaffitzel for the project organiser Kenniscampus Leeuwarden. These are girder bridges with plank cladding and a wooden surface covered with poured asphalt. The bridges have gone down well and in 2011 an order was placed for the design of a larger bridge for bicycle traffic that matched the three existing bridges. This time the order also included the design of the bridge's appearance.
The planks used as cladding for the three completed bridges provided the inspiration to give the new bridge the appearance of a Viking ship lifted out of the water. These long, broad and long ships had a hull consisting of thin, narrow planks on thin ribs to make them as light as possible. They were able to carry many people and goods and stay fast even with a shallow draught.
The new bridge was given the same design characteristics: a concrete surface and a bearing core made of a single laminated beam. A slender construction that can be seen through and offers enough space for hikers, cyclists and viewers. This bridge is expected to be completed in the spring of 2013.