– I don’t think there are any other bridges in the whole world that are made in the same way. That’s what Tormod Dyken, former chief engineer at the Directorate of Roads, says. He helped plan Tretten bru. It collapsed on Monday, just ten years after it was completed. PARTICIPATED: Tormod Dyken was involved in planning Tretten bru. Photo: Statens vegvesen Many have scratched their heads. The police are investigating the matter. How could that happen? Tormod Dyken has a hypothesis. It was Gudbrandsdølen Dagningen who mentioned the case first. The materials expand in the heat Tretten bru is a wooden truss bridge, which was completed in 2012. Dyken believes it is important to look at how the bridge differs from other bridges. It is not a pure wooden bridge, like the other truss bridges in Norway. It consists of both steel and wood. They are two materials that behave differently, especially when temperatures change. STEEL AND WOOD: Here you can see one of the junctions where the wooden beam meets the steel beam. Photo: Lars Erik Skrefsrud / news Steel expands faster than wood, says Dyken. – Then a compulsion arises. This means that the wood must stretch to keep up with the steel in the expansion. It can create small cracks in the nodes. The more times the temperature changes occur, the bigger the cracks become. Dyken believes that this is what happened at Tretten bru. The cracks have grown, and the bridge has been stressed over time. That is why it collapsed ten years after it was built. A unique bridge The Norwegian Public Roads Administration decided to close all the other truss bridges for three days on Tuesday afternoon But these are not really built in the same way as the Thirteenth Bridge, says Dyken. None of them have the same combination of wood and steel. – I don’t think there are any other bridges in the whole world that are made in the same way. He therefore believes that closing the 14 wooden bridges would be a bit blind. – If my hypothesis is correct and is confirmed, then the other bridges can be opened immediately. Then it has nothing to do with how they are built. Still, he can understand that the Norwegian Road Administration follows the precautionary principle. – Then they have done something to avoid ending up in the gap if something were to happen. Read what Innlandet county council says about the closed bridges further down in the article. But if the former chief engineer’s hypothesis turns out to be true – Shouldn’t that have been thought of when Tretten bru was built? – Should have reacted Tensions in the nodes are completely trivial individually, says Dyken. He says that those who planned and built the bridge were clear about what they were doing. Computer analyzes were run to calculate the forces in the framework. But this with temperature changes, he believes, was hardly included in such an analysis. Because it takes some thinking that it could become a problem, he believes. – You have never heard of it before, because there are no other such bridges. HYBRID BRIDGE: Thirteen bridges are unique. It is built with a combination of steel and wood. Photo: Marte Iren Noreng Trøen / news Despite the fact that it was difficult to predict that a collapse could happen, the former chief engineer feels a little stupid. – Now in hindsight, perhaps I should have reacted to it. He also emphasizes that this is something that cannot be picked up during an inspection. The cracks are formed on the inside of the wood. The bridge was last checked in June. Then there was nothing to suggest that it would collapse only two months later. Introducing measures Innlandet county council has initiated measures after several truss bridges in the county were closed. They state this in a press release on Thursday afternoon. The closure of the fountain has led to increased traffic on the bypass roads. – As a result, we have implemented traffic safety measures and are continuously assessing the need for further measures. That’s what section leader Alfred Gullord in Innlandet County Municipality says in the press release. CLOSED: Norsenga bridge in Kongsvinger is one of the bridges that has been closed after the collapse at Tretten. Photo: Ann-Kristin Mo It is currently unclear how long the bridges will be closed. The police are still investigating the bridge collapse at Tretten. It is still unknown what the cause is.
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Former chief engineer describes Tretten bru as unique – thinks closing 14 bridges is unnecessary – news Innlandet – Local news, TV and radio
