Norway’s wooden bridges span increasingly large lakes / Columns / The Foreigner

Norway’s wooden bridges span increasingly large lakes. Bridges are prominent in Norway’s infrastructure. There are more than 25,000 in the country in all – nine in ten for roads, and one in ten for railways. The oldest ones are made of stone, most of the newer ones of concrete and steel. Wood has come into bridge building recently, and there now are some 200 wooden bridges in Norway. A record-breaking one is coming. The bridge will extend over Mjøsa, Norway’s largest lake and the 35th largest in Europe.  Lago de Garda in northern Italy comes one place ahead. The Norwegian lake was a vital transport route before railways and long-distance roads were built, and the cities of Gjøvik, Hamar and Lillehammer grew up along its shores. The forthcoming bridge will be located in Aksershus, Oppland and Hedmark Counties, oriented more or less north-south, stretching 117 km from Lillehammer in the north to Minnesund in Eidsvoll in the south. It will be 15 km wide at its broadest near Hamar.

norwayroads, norwaytraffic, bridgesnorway



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Norway’s wooden bridges span increasingly large lakes

Published on Monday, 18th November, 2013 at 14:12 under the columns category, by M. Michael Brady.

Bridges are prominent in Norway’s infrastructure. There are more than 25,000 in the country in all – nine in ten for roads, and one in ten for railways. The oldest ones are made of stone, most of the newer ones of concrete and steel. Wood has come into bridge building recently, and there now are some 200 wooden bridges in Norway. A record-breaking one is coming.

Planned bridge over Lake Mjøsa
Planned bridge over Lake Mjøsa
Photo: Norwegian Public Roads Administration


The bridge will extend over Mjøsa, Norway’s largest lake and the 35th largest in Europe.  Lago de Garda in northern Italy comes one place ahead. The Norwegian lake was a vital transport route before railways and long-distance roads were built, and the cities of Gjøvik, Hamar and Lillehammer grew up along its shores.

The forthcoming bridge will be located in Aksershus, Oppland and Hedmark Counties, oriented more or less north-south, stretching 117 km from Lillehammer in the north to Minnesund in Eidsvoll in the south. It will be 15 km wide at its broadest near Hamar.

There’s no water-borne traffic on the lake today, aside from the veteran steamship Skibladner tourist route and pleasure boating. Traffic along the lake goes by road and rail and traffic across it is on bridges. The longest bridge is Mjøsbrua that carries the E6 highway across the lake between Biri on the west shore and Moelv on the east shore.

Opened in 1985 to replace a former ferry route, it now operates at capacity, so a new bridge is needed. It will augment the two-lane Mjøsbrua and provide the cross-lake traffic capacity for the widening of E6 to four lanes called for in the 2014-2013 National Transport Plan.

Statens vegvesen, the Norwegian Public Roads Administration (NPRA), has projected a new bridge with a wooden structure located near to the existing Mjøsbrua one – the 196-metre Flisa Bridge across the Glomma River, currently the world’s longest wooden bridge. The new bridge, with a total length of 1.4 km, will be seven times as long.

Wooden bridge structure technology has been well-proven, with the Flisa Bridge having been in service for more than ten years. Wood was also chosen for the new bridge’s structure because it outperforms steel.

This seemingly counterintuitive advantage comes about because wood used in bridges is laminated  and sealed to keep its moisture content under 20%. Ordinary timber is subject to rot, softens if not treated, and wood decay fungi become active above this percentage. Moreover, laminated wood trusses don’t rust and hence don’t need periodic repainting steel ones do.

Structurally the new bridge over Mjøsa is said to be extradosed, best described as a cross between the traditional cable-stayed bridge and girder bridge architectures. The term extradosed comes from extrados, the architectural term for exterior curve of an arch – from the French extradossé. Extradosed architectures are increasingly being chosen for new bridges. At this writing, the latest is the 808 metre-long bridge over the Vistula River at Kwidzyn, Poland that opened in July 2013.

As conditions for the new bridge are favourable, a technical feasibility study was initiated in September 2013 to thrash out the details. With a total budget of NOK 13 million, funded 50-50 by NPRA and Innovation Norway, the study aims to clarify design aspects. This includes a choice of one of two proposed alignments over the lake, and choice of traffic sharing between the existing and new bridges.

Two approaches to traffic sharing have been proposed. The new bridge might have two lanes, to provide the four lanes for the E6 highway in concert with the existing bridge. Or, it might have four lanes dedicated to the E6, while the existing bridge takes local traffic across the lake.

Facts:

  • The planning, building and lifetime operation of timber bridges has clearly become a challenging high-tech sector within structural engineering.
  • The Norwegian University of Science and Technology in Trondheim now offers a doctoral programme in timber structures. Scholarships for doctoral studies are available.
  • The next deadline for application is 25th November 2013.


Published on Monday, 18th November, 2013 at 14:12 under the columns category, by M. Michael Brady.

This post has the following tags: norwayroads, norwaytraffic, bridgesnorway.





  
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