Norway’s highways authority has selected its preferred design concept for what will be the world’s longest floating bridge, over the 550-meter-deep Bjørna fjord south of Bergen. International contractors are already expressing interest in the potential design-build contract for the roughly 5-kilometer-long bridge, which is expected to open for bidding in 2022.
Two teams of design firms, which each studied four floating concepts, converged on the same preferred option, which was recently chosen by the Norwegian Public Roads Administration (NPRA). The firms are now refining designs and cost estimates for the anchored single-curved, multi-pontoon crossing.
With an estimated construction value of about U.S. $1.3 billion, the Bjørnafjord bridge will include a 300-m-long suspended navigation span with 45 m headroom at the south end, with a land-based A-frame pylon. A northbound string of 40 steelwork pontoons spaced 100 m apart will complete the crossing.
At least three of the pontoons will be anchored with up to six moorings each, says Mathias Egeland, NPRA’s technical development project manager for the E39 route's floating crossings. The pontoon string will curve inland eastwards, away from the strongest winds from the west. “Wind is actually as much a dominant factor as waves and currents,” he adds.
Starting last year, a consortium of Aas-Jakobsen, COWI, Multiconsult and Johs Holt, and another of Dr.techn.Olav Olsen and Norconsult studied designs for tethered and untethered single curved bridges, a double curve variant and a straight crossing.
The chosen, singly curved tethered option is the “concept where we have least risk and where we see the lowest price,” says Egeland. The straight crossing option lost favor also because of the need to manage high thermal expansion in such a long steelwork structure, he adds.
Previously considered to be impossible, the “cutting edge” floating project is now a real project, says Svein Erik Jakobsen, executive project manager at Aas-Jakobsen. He declines to go into more detail until later in the development.
Just as the project has been managed by Scandinavian firms, NPRA hopes to keep steel fabrication within Norway. While recent projects involved Chinese steel, the authority hopes to bring down Norway's high labor cost component with increased automation. “Norway still has some steel production going on connected to the offshore (oil and gas) industry and the shipyards,” explains Egelend.
The Bjørnafjord studies follow investigations for a theoretical crossing of the Sogne fjord, about 100 km north of Bergen. In up to 1,250 m of water, the 3.7-km crossing was deemed to be the most challenging and acted as proof of concept rather than a precursor to construction, says Egeland.
The Bjørnafjord bridge, plus the roughly 27-km-long, twin-bore Rogfast tunnel under the mouth of the Bokna fjord, will eliminate slow ferry crossings on the E39 route between Stavanger and Bergen, cutting journey times to 2 hours, from 4.5 hours, according to NPRA. Earlier work on the Bjørnafjord eliminated a floating tunnel option three years ago.
The projects are part of a long term plan for fixed links at all seven water crossings along the 1,100 km E39 between Kristiansand and Trondheim, valued at U.S. $37.4 billion at 2016 values.