21 September 2022 at 12:56 Preliminary report on the bridge collapse at Tretten The National Accident Investigation Board has come up with a preliminary report on the bridge collapse at Tretten. It does not say what was the direct cause of the bridge collapse, but deals with preliminary findings. SINTEF has retrieved bolts from the river and examined them. All of the bolts have fractures caused by stretching/bending movement in the longitudinal axis of the bolts. There are no signs of fatigue or previous damage to the bolts. Overall, this indicates that the bolts have broken as a result of overloading when the bridge collapsed, the preliminary report states. At this point in the investigation, it cannot be ruled out that bolts other than those examined may have been subject to fatigue or defects that have developed over time. Two-thirds of the bridge is still under water. It is estimated that it will take between four and six weeks before all the parts are recovered and secured.
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