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Not sleepless in Seattle
Ongoing installation of noise-reduced modular expansion joints on the SR 520 West Approach Bridge, Washington State.
The Governor Albert D. Rosellini Bridge-Evergreen Point (commonly called the SR 520 Bridge) is the world’s longest floating bridge, and carries State Route 520 across Lake Washington from Seattle to Medina. The main floating structure was renewed between 2013 and 2015, featuring a number of TENSA®MODULAR expansion joints as described in the project reference sheet.
Associated infrastructure works are ongoing, including construction of a West Approach Bridge. The northern section of this new approach bridge is expected to be completed in the summer of 2017, and will carry westbound cars, buses and trucks from the new floating bridge to the Montlake area. mageba is supplying seven TENSA®MODULAR expansion joints for this new structure, with between six and eight individual movement gaps per joint – the largest accommodating longitudinal SLS movements of 25 in (640 mm). Modular joints are often the ideal expansion joint solution for roadway bridges, especially in the case of bridges with large longitudinal movements, particularly when combined with transversal and even vertical movements. However, the modular joint’s design, with straight-edged transverse surface beams that are hit by the tires of over-rolling traffic, results in a certain amount of noise – which may be problematic, depending on the joint’s location.
To tackle this problem in the case of the new West Approach Bridge, the joints are equipped with noise-reducing “sinus plates”, which create a continuous, smooth driving surface and thus minimize vibrations and noise from the joints’ surface by up to 80%. This project represents the first time noise-reducing sinus plates have been used in the United States, and it is expected that many other authorities will specify their use in the future as the benefits become more widely recognized – and as the demands of the people living in residential areas near bridges become louder.
The joints also feature ROBO®MUTE noise reduction, which encloses the area directly beneath the joint, preventing the transmission of noise from this alternative source. With these high-quality optional solutions selected to tackle the noise emanating from both above and below the expansion joints, the residents of the adjacent city suburbs can rest easy, confident that their sleep will not be interrupted by noise from the new bridge’s expansion joints.
