E39 across Bjørnafjorden. Concept: straight, side-anchored pontoon bridge. Illustration: Norwegian Public Roads Administration

Norwegian Public Roads Administration recommends pontoon bridge over Bjørnafjorden

The Norwegian Public Roads Administration has completed the concept design phase for the Stord-Os section of the E39 highway. In its recommendation to the steering committee for a ferry-free E39, it recommends going ahead with a pontoon bridge across Bjørnafjorden. Multiconsult has been given responsibility for investigating one of the two concepts that will be taken forward to the next stage.

The Stord-Os section of the E39 is one of the subprojects within the larger E39 Stavanger-Bergen project. The plan is to carry out major upgrades to this route, including replacing all of the ferry crossings with bridges or tunnels. The strategic goal is to improve ties between the big cities in Western Norway and within the region as a whole. The big challenge in this subproject is to come up with a way of crossing Bjørnafjorden, a fjord that is around five kilometres wide.

Cost reduction

In autumn 2016, the Norwegian Public Roads Administration launched the third development phase for the Bjørnafjorden crossing, and Multiconsult was awarded the contract for taking the concept “straight, side-anchored pontoon bridge” further. This concept involves a straight bridge floating on pontoons, as well as a cable-stayed bridge at the southern end. Some of the pontoons are side-anchored using cables tied to anchors on the sea bed. The Norwegian Public Roads Administration has announced that the cost of a pontoon bridge will now be NOK 17 billion. Previously the cost of the bridge was estimated at between 20 and 25 billion kroner.

Detailed study

A detailed study has been carried out with the aim of verifying whether it is feasible and cost-effective to use a straight, side-anchored pontoon bridge for the Bjørnafjorden crossing. The concept design has resulted in a proposed bridge that is around five kilometres long with the pontoons approximately 125 metres apart. At the southern end of the crossing there is a large cable-stayed bridge across the shipping lane. The bridge is laterally stiffened with anchor cables tied to four of the pontoons. The southern end of the bridge is fixed in place, while the north end can move freely lengthways.

Working together

Multiconsult has produced this concept design in collaboration with the companies Aker Solutions, Johs Holt, NGI, Entail and Rambøll.

The project group has been created to ensure experience transfer and continuity between the concept development phases, as well as being a repository for leading expertise and experience in all of the disciplines involved such as marine geotechnics, hydrodynamics and floating structures, permanent anchoring systems, marine operations and cable-stayed bridges.

Multiconsult’s own bridge partners Michel Virlogeux and T-engineering also participated somewhat initially, by offering their comments on the concept.

About Bjørnafjorden

Bjørnafjorden is a fjord in the county of Hordaland that runs through the municipalities of Austervoll, Fusa and Tysnes. It is around 30 kilometres long, with a maximum depth of over 580 metres.