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Engineering dynamics

Successfully reducing noise on Stockholm rail bridge.

Rail bridge at night

  • Client

    Client: VIBRATEC (Vibratec Akustikprodukter ApS)

  • Asset

    Rail bridge

  • Location

    Stockholm

Overview

Vibratec provides solutions for noise and vibration control and reduction. Trafikverket (Swedish Transportation Administration) enlisted the help of Vibratec to support on a noise reduction project for a monumental Stockholm railway bridge. LR’s Engineering Dynamics team assisted Vibratec with technical support. We have a long and positive history of collaboration with Vibratec for noise and vibration problems.

Reducing noise from a busy Stockholm bridge was a priority for the Swedish Transportation Administration (Trafikverket). The 90+ year-old Gamla Årsta bridge had been refurbished and train pass-by noise had increased significantly as a result.  A solution had to be put in place which would not impact on the trains crossing the bridge, which run every six minutes, 24 hours per day. Also, installation of the solution could not be allowed to interfere with the traffic.

How we helped

Vibratec’s staff has a high level of noise and vibration insight, but limited capability for modelling and measurements. This is a good match for our noise and vibration expertise together with our advanced modelling capacity and large collection of instrumentation. For the Gamla Årsta bridge project we applied our acoustic insight to devise a dedicated investigation. This mapped the governing physical and acoustic mechanisms causing the excessive noise, which allowed us to design a targeted noise mitigation solution.

After a comprehensive pre-study investigation, we advised Vibratec and Trafikverket on the best suited noise mitigation solution, without access to the deck top-side to ensure it did not impact on traffic.  Vibratec’s idea was to introduce an add-on constrained layer damping (CLD) solution, and from a thorough pre-study (with different configurations and at different temperatures), a new multi-patch configuration could be identified as optimal. Our research included numerical modelling using Statistical Energy Analysis (SEA), microphone array measurements, structural dynamics measurements, and various noise and vibration measurements. Testing in LR’s climate chamber showed that this would perform consistently across the typical wide temperature range of Stockholm.

After the CLD solution had been installed on the bridge, we performed new measurements and documented a substantial noise reduction of 5-6 dB, measured across various locations.

Working closely with Vibratec throughout we ensured a collaboration approach, allowing for optimised planning and approach adjustment.

Expertise applied:

  • Acoustic insight

  • Application of a broad range of techniques for the investigation, both numerical and empirical

  • Non-textbook solution of complex problem

  • Compliance with challenging project parameters

The impact

A satisfactory noise reduction of 5-6 dB was obtained and documented, as well as the solution being implemented without any disruption to the transport services.  Due to the success of this project we have also co-authored three conference papers with the client on this project.

Proof points

  • Noise mitigation solution provided with no impact on traffic

  • Noise mitigation measures which will perform consistently across all range of weather conditions typically present in Stockholm.

The successful noise reduction of the Gamal Årsta bridge was the result of efficient collaboration between Vibratec and LR’s acoustic experts. It is in line with past successful projects done together. We look forward to LR’s continued assistance for further developing our noise mitigation solutions.

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