Here is another example of an amazing wooden construction. The master’s 500 year old design and a contemporary artist’s dream turned into a unique wood construction, a pedestrian bridge outside Oslo, Norway.
In 1502, Sultan Bayezid II, ruler of the Ottoman Empire in Constantinople, planned to build a bridge crossing The Golden Horn, connecting Europe and Asia. Leonardo da Vinci proposed a design of an arched stone bridge with a span of 240 meters. At that time the longest stone bridge span was 37,5 meters. If the Sultan hadn’t turned it down, it would have been one of the world’s wonders. But he did, and the sketches remained in the archives for several hundred years.
In 1996, the renowned Norwegian artist Vebjørn Sand saw the drawing at an exhibition showing Leonardo’s engineering designs. It sparked an idea, and he initiated The Leonardo Bridge Project (www.leonardobridgeproject.org). Back in Norway, Sand managed to convince the Norwegian Public Roads Administration to build a bridge based on Leonardo’s design.
In Norway, the tradition of building with wood goes back thousands of years and the oldest wooden buildings stand since over 800 years. In the early 1990s, the Norwegian glulam producer Moelven Limtre had developed technology to produce glulam beams for the construction of the halls for the winter Olympics in Lillehammer in 1994 ( e.g. the Viking Ship, http://www.hoa.no/en/the-viking-ship/). This could also be used for building bridges.
The decision was made to build a wooden, pedestrian bridge crossing the main road E-18, in ÅS, southwest of Oslo. The bridge was scaled down to a total length of 110 meters, with a main span of 40 meters, still keeping in line with the construction principles of the original design. The construction consists of a vertical center arch, and two tilted side arches connected at the top. The arches are fixed to concrete foundations in the ground. The three arches consist of 90 m3 of glulam, in addition to 120 m3 of glulam in the bridge deck.
As the bridge is also a work of art meant to provide an esthetic experience for the travelers, it was decided not to cover the construction, and to treat the wood only with environmentally friendly oil and wax based impregnation and varnish. In that way, a light colored, visible surface was obtained. The service-life of the bridge was estimated to 40 years, as opposed to the standard 100 years for wooden bridges which have received constructive and chemical protection.
The bridge was opened in 2001 by the Norwegian Queen Sonja.
Wood is an excellent building material. However, it is well known that natural wood directly exposed to the weather, and with no possibility to dry completely, will deteriorate over time. This is part of the natural life cycle. Also, wood that is exposed to variations in moisture content, like in the natural climate in Norway, will develop natural cracks due to swelling and shrinking. Wood is a “live” material. This is also true for the Leonardo Bridge, and after about five years, fungi were discovered in cracks in the wooden beams that were not protected.
The fungi had not weakened the structure, and the problem was solved by covering the top of the beams with steel sheeting. In my opinion, this has not harmed the esthetical value of this exceptional structure, and will extend its service life considerably.
1 m3 of wood stores about 1 ton of carbon dioxide, so as long as this bridge stands, it will store 210 tons, thus helping reduce global warming. By choosing wood and wood based products, you get beautiful, durable and practical articles, and you contribute to the well-being of the planet and future generations. And when it is worn out, you just put it back into the natural cycle of life.
That’s why wood is simply brilliant.