Sleep well in Seattle

mageba has now completed the installation of noise-reduced expansion joints in the new South Structure of Seattle’s SR520 West Approach Bridge – similar to the silent joints that were installed in the North Structure in 2016/2017 to minimise noise disturbance from traffic crossing the world’s longest floating bridge.

When the Evergreen Point Floating Bridge (also known as the SR520 Bridge), which opened in 2016, was constructed to replace an existing structure, mageba supplied nine TENSA®MODULAR expansion joints to accommodate the large movements that can arise in a floating bridge of length 7,710 ft (2,350 m). The largest of these expansion joints has 16 individual movement gaps and allows 48.4 in (1,230 mm) of longitudinal movement in service conditions, or 70.4 in (1,790 mm) of extreme limit state movement.

In 2016/2017, when the North Structure of the floating bridge’s West Approach Bridge was built, closer to the city’s residential areas, it was decided to minimise the noise from the required TENSA®MODULAR expansion joints by fitting them with noise-reducing surface plates to bridge over the joint’s movement gaps (creating a continuous driving surface), and also equipping them with a ROBO®MUTE noise protection system beneath each joint (encapsulating the space beneath the joint and inhibiting the spreading of noise from the joint’s underside). These methods of noise reduction are described in some detail in a previous newsletter article.

Today, construction is being completed on the South Structure of the West Approach Bridge, and once again, noise-reduced TENSA®MODULAR expansion joints (featuring both surface plates and ROBO®MUTE) have been used in the construction – a vote of confidence in the quality of the expansion joints installed to date and in the effectiveness of their noise-reduction features.

Thanks to the efforts of the responsible bridge engineers in specifying the use of these quiet expansion joints and ensuring their proper design and installation, any noise from traffic crossing the bridge will be greatly reduced – enabling the people of Seattle to always get a good night’s sleep!  

Bridge designer: TY Lin International
Contractor: American Bridge, Graham
Owner: Washington State DoT

The Evergreen Point Floating Bridge (SR520 Bridge) in Seattle, Washington was constructed using TENSA®MODULAR expansion joints with up to 16 individual movement gaps

The South Structure of the SR520 West Approach Bridge is being constructed with noise-reduced TENSA®MODULAR expansion joints accommodating its movements and rotations

© Washington State Department of Transportation

For this project, mageba designed and manufactured six noise-reduced TENSA®MODULAR expansion joints, each with between four and seven individual movement gaps

Lifting of a TENSA®MODULAR expansion joint into position on the new South Structure of the SR520 West Approach Bridge

The expansion joint is lifted into a carefully prepared block-out in the bridge’s superstructure, where it will be concreted in place

View from below of a seven-gap TENSA®MODULAR expansion joint following positioning in the deck of Seattle’s SR520 West Approach Bridge

The noise-reducing “sinus plates” (so-called for their sine-wave shape) bridge over the modular joint’s individual movement gaps, creating a continuous driving surface for vehicles – avoiding wheel impacts and therefore minimizing noise