Update On Noisy Bridge Joints

The Laurelhurst Community Club (LCC) recently published this information in their newsletter:

How to Fix Noisy Bridge Expansion Joints? 

Expansion joints on bridges and highways are essential for safety, but they also generate noise to nearby residents and adjacent public park users. The newest and most glaring example of loud noise up to 90 decibels is the SR520 floating bridge. 

To find the cause of the noise and target solutions, WSDOT received funding for a grant from the State Transportation budget for the University of Washington’s mechanical engineering department to conduct research. These findings will enable WSDOT to refine its best practices and construction specifications to prevent joint noise on future state-wide infrastructure projects. 

LCC trustee McAleer and former trustee Jean Amick attended the results presentation in February. With hands-on measurements devices, photo documentations, sound recordings and observation on the SR520 Bridge, UW engineers concluded that most of the noise is actually generated from “the top” of the expansion joints, and not from underneath the joints as presumed earlier. 

The noise is linked to the width of the tires hitting the air gaps between the fixed center beam metal parts on the expansion joint. This action is called Energy Spectural Density (EDS). The study found that the narrower the tire width, the more EDS, resulting in higher megahertz (high pitch) sounds. 

The UW team recommended two potential solutions to fill the air gaps that could be installed retroactively on the SR520 bridge – and potentially other similar state-wide bridges and highways – that could reduce the noise emitted by at least five to 10 decibels.  

One involves a plate system that may not withstand the motion stress of a floating structure; the other is insertion of a pre-compressed foam that deteriorates and requires continual maintenance. 

UW engineers propose to develop a new flexible sound-absorbing system to fill the air gaps and absorb the energy produced. They are requesting a funding grant, which would require approval in the 2019 State Legislative Session, to develop materials and testing.  

Please contact your legislators and urge them to allocate funds to improve the expansion joint systems. Contact: David.Frockt @leg.wa.gov and Gerry.Pollet@leg.wa.