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In February 2024, the Thorstedvej overpass over Oddesundvej in Thisted was hit by a special transport carrying a wind turbine nacelle. The bridge suffered extensive damage and at first appeared to need full replacement. Instead, SYSTRA’s analysis showed that the superstructure could be repaired.
Repair instead of replacement
The bridge superstructure sustained extensive damage in the form of a semi-circular punch-through failure measuring approximately 7 x 5 metres on one side of the bridge deck. The bridge is a post-tensioned frame bridge dating from the early 1990s. SYSTRA won the tender for replacement of the bridge, as it had been assessed prior to the tender process that the bridge could not be saved.
Based on preliminary calculations, SYSTRA approached the Danish Road Directorate regarding the possibility of repairing the superstructure instead. The motivation for repairing the bridge rather than replacing it was both financial savings and a sustainability benefit.
Damage mapping using iPhone scanning
During an inspection of the damage in the summer of 2024, SYSTRA carried out a simple 3D scan using an iPhone with a LiDAR scanner. The scan provided a fast and effective way to map the extent of the damage and made it possible to determine the position of reinforcement and cables with relatively high accuracy back at the office. The resulting point cloud was then combined with the original design drawings as a basis for the analysis.
Assessing the damage
The damage had exposed several of the post-tensioning cables, which also meant that the cable profile had changed and a new state of equilibrium had been established. The analysis therefore had to take into account how the post-tensioning forces had been redistributed within the bridge deck.
The analysis of the damaged structure indicated that the extent of the damage was just limited enough for the stresses in the bridge deck to remain within the allowable stress level. The design also had to account for the differing material properties between the original structure and the new concrete casting, as well as differential movements caused by shrinkage and creep. This was addressed through a two-stage analysis in a FEM program.
The repair scheme was then developed with a focus on minimising intervention in the undamaged concrete.
A sustainable and cost-effective solution
The repair of the Thorstedsvej bridge has attracted considerable attention across the industry.
The project shows that it is not always necessary to build new structures and that, in many cases, an alternative solution can be chosen that is both more cost-effective and more sustainable.
Julie Bernth, Head of Bridges and Structures, has given several presentations on the bridge repair, including at Betonreparationsdagen 2024.
