Norway’s first bridge made of SSAB Weathering 420 ML: Elverhøy

The Elverhøy Bridge is on National Road 70 in Sunndal, in the central region of Norway. It is surrounded by a host of snow-clad mountains and the Driva river, which flows under the bridge. 

“Since the Driva is an important river for salmon fishing, there were restrictions on how we could construct this bridge. One major benefit in our choice of weathering steel is that we don’t need to paint the material, so no paint residues will make their way into the river,” explains Cato Dørum at the Norwegian Public Roads Administration. 

The old bridge was too narrow and in poor condition; it had been built in 1942 , so it was high time to demolish it and build a new one. The connection is important. Sunndal is an important industrial region, one activity being the production of aluminum. A lot of transport operations need to use the bridge over the Driva every day.

SSAB Weathering 420 ML – ideal for welding 

The Norwegian Public Roads Administration wanted a high-strength material, which is why SSAB Weathering 420 ML was chosen for the structure. 

“Building with SSAB Weathering 420 ML gave us a high-strength steel with outstanding fatigue properties. We were able to reduce the volume of steel, while still maintaining its high strength. Less steel means fewer transport operations, which also reduces carbon dioxide emissions,” says Cato Dørum.

Modern welding techology was used to mount the superstructure onto concrete foundations. 

Laser welding of prefabricated SSAB Weathering panels took place in a Norwegian plant using automated robots to produce strong, precise weld joints. It also saves time. 

“The technology means that welding can be performed more quickly and that the joints have higher fatigue resistance compared with normal welding. This means that the bridge is cheaper when compared with traditional welding methods,” explains Cato Dørum.

This is the third bridge in Norway to be built in this way. The Frønes Bridge and the Ya Bridge also used automated robot welding in connection with production. 

Part of a research project

The construction of the Elverhøy Bridge has been part of a research project. 

“In our research, we’ve looked at issues including how we can develop welding and construction methods while reducing carbon dioxide emissions. The Elverhøy Bridge has served as a pilot project, where we also conducted various fatigue trials, to make sure that the structure is sufficiently durable and stable,” says Cato Dørum. 

The site of the Elverhøy Bridge was also a decisive factor in the choice of material. The unique feature of SSAB Weathering and weather-resistant steels is that a protective, rust-like coating is formed on the surface of the steel, a patina that protects against the elements. Wind and rain simply make the protective coating even stronger. 

Reduces the environmental impact  

Sustainable construction is becoming increasingly important. It’s important to invest in materials that generate lower carbon dioxide emissions and are longer lasting. 

As weathering steel does not need to be painted, the environmental impact is reduced and paint residues in water bodies are avoided. The steel can be painted if desired, but the interval between repainting is double that required for other kinds of steel. 

“Weather-resistant steel is also sustainable and requires less maintenance. A bridge should be able to last 100 years, and this is why we believe in building with SSAB Weathering. The material has a lower life cycle cost than many other materials, and contributes to reduced carbon dioxide emissions, as it requires so little maintenance,” says Cato Dørum. 

The rough, natural appearance that changes as the surface ages is created by the oxidization process. It occurs as the steel is exposed to alternating damp and dry conditions. The whole process takes between two and six years. If the surface is scratched, it heals itself, i.e., the patina will form once more.

Good drainage required  

There are, however, a few things to bear in mind for anyone wanting to build a bridge using SSAB Weathering. The material should not be exposed to direct contact with salt. 

“This is why you need to think carefully when designing the details of a bridge. There has to be good drainage in order to avoid water collecting and salt on the steel surface,” advises Cato Dørum. “Another tip is to add a rust allowance to the surface of the steel, to make the panels used a little thicker than the ones proposed.” 

The Elverhøy Bridge was completed in December 2023, and traffic is now using the new bridge. 

“It’s been a major, time-consuming job with lots of parts to deliver, but we’ve had close collaboration with the customer, which has worked really well,” says Barbro Garen at Tibnor. 

Cato Dørum agrees: 
“We’re really pleased with the outcome, it’s been an efficient process, with good collaboration with SSAB and the supplier, Tibnor. We’ll be happy to build using SSAB Weathering again next time, and in the future, we hope to be able to take the next step and build using fossil-free steel,” he concludes.  

Benefits of building a bridge using SSAB Weathering

• High corrosion resistance
• Low life cycle costs thanks to minimal maintenance 
• No chemical or paint emissions since the material does not need repainting at regular intervals.
• Efficient construction with prefabricated steel components
• A unique structure that blends nicely into the natural surroundings