Design and Testing of Modular Expansion Joint Noise Mitigation Strategies

This investigation focuses on the design and feasibility of noise mitigation strategies for installation in modular expansion joints (MEJs) on highway bridges. Expansion joints are necessary for effective bridge function but contribute greatly to surrounding noise pollution. The three primary sources of noise from MEJs identified include the resonance of the air within the gaps, the resonance of the beams, and the resonance of the tires. By incorporating engineered chevron support structures into the gaps of the MEJs, the research demonstrates the feasibility of significantly reducing noise emanating from MEJs. The novel chevron design flexes to expand and contract, matching the movement of the roadway but resisting vertical loading from cars driving overhead. The noise reduction treatment was applied to a westbound lane of the east MEJ on the SR 520 floating bridge across Lake Washington, connecting Seattle with the city of Medina, for a 2-month evaluation period. According to energy spectral density data collected from roadside audio recordings, this solution proved to be highly effective. At a distance of 160 ft from the joint, a noise reduction of more than 10 dB in the 500–900 Hz frequency range was recorded. Beyond 500 ft, the distinction between noise from the concrete road surface and from the MEJ diminished to the extent that it became challenging to discern when individual cars traversed the MEJ.