Today, travelling from Kristiansand to Trondheim on Norway’s west coast, a trip of over 1,000 kilometres, takes an entire day by car - thanks to eight ferry crossings over the fjords along the way. Now the Norwegian Public Roads Administration (NPRA) wants to minimise travel time by building a series of bridges to cross the fjords.
One particular fjord, the Bear Fjord (Bjørnefjorden), is extremely deep and therefore requires a bridge built on floating pontoons to span the five kilometre stretch. Such a long pontoon bridge has never been designed before and could cause a potential risk for shipping. Because of this, the NPRA has asked Ramboll’s Risk & Safety department (in the Transport Rail Division) to provide a ship collision analysis.
Three different designs
According to Søren Randrup-Thomsen, Head of Department, Risk and Safety at Ramboll, selection of the final bridge design is dependent upon the results of the collision analysis.
”During the next six months, we will analyse the risk of collision for three different potential bridge designs over Bear Fjord,” he explains. “We study existing data about ship traffic on the fjord so we can evaluate the risk of collision for the three potential designs.”
After analysing extensive data records of the existing maritime traffic, a team of consultants from Ramboll will then develop a ship collision model that can determine the probability of collision with the bridge pontoons and superstructure, as well as providing bridge designers with a ship collision load specification they can use when designing the bridge.
Just to complicate matters, the analysis also has to take into account submarines. The Norwegian military carries out submarine exercises in Bear Fjord and because the bridge’s floating pontoons are anchored to the seabed with wires, there is an increased risk of collision.
”We did a similar ship collision analysis of the bridge over Sognefjord from 2011 to 2013,” says Søren Randrup-Thomsen, “and now we have won the project for Bear Fjord. With these two projects, we have established excellent cooperation with the NPRA, putting us in a good position for future collision studies in connection with the project “Ferry-free E39 in Norway.”
The project is carried out in collaboration with Ramboll’s Bridge and Risk divisions in Norway.