Kirjalansalmi bridge health monitoring

In 2023, the Finnish Transport Infrastructure Agency (FTIA) embarked on a project to construct a new 600-meter-long cable-stayed bridge, set to replace the Kirjalansalmi bridge built in 1963. To ensure the safety of the old bridge in its last years of operation, Koherent’s sensors have been used for monitoring its movement and vibrations since 2023.

FTIA is responsible for developing and maintaining the state-owned road network, railways and waterways in Finland, with an annual budget of approximately 2.1 billion euros.

The Kirjalansalmi bridge is located in the Nordic archipelago, where the harsh weather conditions pose significant challenges to optical monitoring technologies. The Koherent sensors, however, provide extremely accurate monitoring regardless of the weather, allowing both gradual movements and rapid vibrations to be detected with unmatched precision.

Our sensors have not only met but exceeded Koherent’s own specifications, proving their reliability throughout several seasons without any degradation in performance despite challenging weather. The system has allowed identification of maximal deflection events and facilitates straightforward trend analysis, ensuring comprehensive structural insights.

Data from our sensors is transferred to the cloud via 4G/5G networks and made available via a robust API for easy integration with partner visualization and analytics tools. The data is additionally archived for further analysis.

“We contacted FTIA’s bridge professionals and told them about our solution. They immediately got interested and proposed to use the system for this bridge. We started the project very quickly after that”, says Sami Thelin at Koherent.

“We measure the movement of one cross beam, lateral movement along three axes and angular movement along two axes. The reference sensors were installed to bridge pillars and the measurement is conducted under the bridge deck. Monitoring started in July 2023“, says CEO Kari Leppänen at Koherent.

“With our solution asset owners and contractors can improve planning and maintenance of expensive infrastructure throughout its lifespan. The financial impact of being able to prioritize asset maintenance projects can be significant”, says Thelin.

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