The Old Lidingö Bridge connects the island Lidingö to the city of Stockholm. For a long time it was the only permanent connection carrying heavy freight trains, road vehicles, and pedestrians. Since 1978 it only carries the tram travelling along the Lidingöbanan and pedestrians, while the new Lidingö Bridge carries road traffic. The number of travellers is, however, large. An average of about 14 000 passengers take the tram every day.
Due to severe corrosion at some of the bridge members and accelerating maintenance costs, the owner of the bridge, the City of Lidingö, has decided for it to be replaced. The immediate safety of the bridge and its functionality until a replacement could be in place has been a concern. To investigate the true structural response under the in-service loads, a long term monitoring campaign was engaged starting 2017.
It consisted of a wireless sensor network with accelerometers, strain gauges and inclinometers. From the recorded data it was possible to assess the condition of critical members of the bridge. The relatively low structural response showed that the present load levels do not imperil the safety of the passengers.
In addition to the direct use of the measurements, the bridge was used as a case study for condition assessment, surveillance and management of critical bridges. The study had a focus on wireless sensor networks for condition assessment and service live prediction. Models for corrosion and fatigue deterioration were developed and damage detection routines based on acceleration data were tested.