Lars Olaf Møller-Hansen
Structural engineerT: +45 5161 7083
A simple rectangular beam, bridging the 60-metre-wide Randselva river. It sounds fairly straightforward, but there is – quite literally – a twist: the structure warps 90 degrees, right in the middle of the free span.
This twist posed a considerable engineering challenge. But with a detailed digital 3D-model, and a bit of an inventive streak, it became buildable.
The structure is a hybrid of bridge, building and sculpture, designed by BIG architects. As part of Kistefos museum and sculpture park, it serves both as an exhibition space and a connection between the north and south side of the grounds, as it spans the river.
A 3D-roadmap to twisting steel
Kistefos Museum's bearing structure is made of steel. Wringing out a dishcloth is a simple task. Now, imagine wringing a 360 tons steel structure in a 90-degree twist. It sounds almost impossible. And it requires a massive amount of steel.
That's why Bladt Industries, the contractor on the project, reached out to Ramboll to assist with making the structure more easily buildable.
Ramboll’s engineers made a digital 3D-model of the structure, where the design and all potential changes were tested. And that payed off. The result was a 35% reduction in steel use – and thereby, a significant cost reduction – and a detailed roadmap for realising the complex structure.
“Every week, we updated the 3D-model to find savings on the steel use. A lot of money was saved that way”, explains Kim Bringsjord, division director for infrastructure in Bladt Industries.
The steel reduction was not only good news for the budget; it also served the environment well, as it saved 490 tons CO2.
As part of the project, Ramboll also developed new standards in the existing 3D-programmes, specifically adapted to the demanding structure, and we revised the 3D-model concurrently with the construction – all of which contributed to making it a smooth and efficient construction process.
1,500 ruler-straight strips fitted on a curve
But there is more to the Twist than steel. When the load-bearing structure was finished, 1,500 straight wooden strips had to be fitted in place inside the 90-degree twist. But how exactly do you keep track of 1,500 strips, when each one is different from the next and designed to fit in only one specific place in the twist?
Again, the 3D-model came in handy.
As it often happens, the reality of the built construction deviated slightly from the projected 3D-model, but the contractor needed absolute accuracy to realise the architect’s vision for the wooden strips. To accomplish this, a new on-site 3D scanning was carried out.
“Using 500 million data points, we converted the scanning to a digital twin of the built steel structure and designed a digital ‘user manual’ for fitting the strips in place” Lars Olaf Møller-Hansen, assistant project manager, explains.
“For this purpose, we also developed our own new digital programme for automated ID-numbering of each strip, carried out physically with a CNC (computer numerical control) wood cutter.”
In this way, installing the 1,500 wooden strips went from a chaotic to a straight-forward process.
“Ramboll’s approach made the process and collaboration incredibly agile. I could just convert their files directly into my system for the CNC-cutter, which definitely made my work easier,” says Paul Østergaard, Vestjysk Modelsnedkeri ApS, who cut the wooden strips.
“Every week, we updated the 3D-model to find kilo savings on the steel use. A lot of money was saved that way.”
- Kim Bringsjord, division director for infrastructure in Blandt Industries.
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