The Jim Stynes Bridge (JSB) is a lightweight structure over the Yarra River providing a vital missing pedestrian, bicycle and commuter link between Melbourne’s CBD with two of the city’s most important precincts, Docklands and Southbank.
The innovative structure utilises tensioned steel elements to form the lightweight underpass nearly 180m long, supported by tension cable members, Engineering Dynamics was engaged to design, manufacture and install 7 different Tuned Mass Damping Systems to reduce footfall vibration for the pedestrian movement across the bridge.
With the design criteria were then agreed with the client, specialist computer software was used to undertake a detailed time-history acceleration response analysis with the first modes of frequency of the structure were within the walking and jogging frequency range.
From this, it was determined that the bridge would require tuned mass dampers to limit the accelerations and prevent resonance.
The computer model subsequently included modelling of the tuned mass dampers, which gave the project team confidence that the dampers would achieve satisfactory results.
In all, seven tuned mass dampers were installed at strategic points along the length of the structure.
After the bridge was constructed and the tuned mass dampers installed, on-site testing was undertaken with over 20 volunteers who marched in time to a metronome, set to the natural frequency of the bridge structure.
Accelerometers were placed on the bridge structure to record the extent of movement.
Analysis of the results showed that the accelerations were within the design criteria set at the start of the project.