As an increasing number of cars, trucks and buses travel the nation's roads and highways, traffic-induced noise pollution has become a major concern for countless local communities. Noise barriers have been embraced by transportation agencies around the country as an effective and safe way to mitigate the negative effects of this growing problem.
However, standard noise barrier materials often create additional dilemmas related to blocking aesthetic views and increasing overall project costs. These challenges were recently encountered by the Ohio Department of Transportation (ODOT) when widening major interstate highways near Columbus and Cincinnati.
When growing traffic made it necessary to widen the Worthington-Galena Bridge north of Columbus and the Nordyke Road Bridge on Interstate 275 east of Cincinnati, environmental assessments revealed the need to install sound abatement systems at both sites. On the one hand, ODOT needed a noise barrier solution able to reduce the impact of increased traffic sound levels on surrounding communities and safeguard people and property in the event of a car crash.
However, ODOT realized that standard reinforced concrete and steel noise barrier materials had serious limitations with respect to two other project necessities. The agency needed a material that could also minimize dead load on the elevated structures and preserve scenic views of nearby churches, trees and rolling hills for drivers.
To meet this range of needs, ODOT decided to construct transparent sound walls using PARAGLAS SOUND-STOP GS CC Noise Barrier sheet, an innovative sound-insulating material from CYRO Industries, a wholly owned subsidiary of Degussa, Parsippany, N.J. Although these sound walls are the first of their kind in the Midwest, PARAGLAS SOUNDSTOP GS CC sheet has been successfully employed by transportation agencies in other parts of the country, including New York.
This product was able to not only provide the transparency and enhanced safety features that ODOT required, but it is also a fraction of the weight of conventional noise barrier panels. This results in a significant reduction in dead load on the bridges, thereby minimizing the extra costs of materials and labor associated with the structural reinforcement that would otherwise have been required.
When considering noise barrier materials for the two bridge projects, ODOT was concerned with weight. The amount of weight per linear foot (dead load) that a construction material contributes is crucial for projects involving bridges and overpasses, because every extra pound adds to the structure's dead load and the need to install extra load-bearing girders for structural reinforcement.
Contributing less than 200 pounds per linear foot, the PARAGLAS SOUNDSTOP GS CC system chosen by ODOT is up to five times lighter than conventional materials. This weight difference allowed ODOT to minimize dead load concerns for the Worthington-Galena and Nordyke Road bridge projects, thereby saving reinforcement costs and labor.
"Our structural engineering department determined that PARAGLAS SOUNDSTOP GS CC Noise Barrier sheet is a great material for bridges because it is not as heavy as concrete or steel noise wall panels, so there is less stress on the bridge. Any material that reduces the stress on our bridges is advantageous," says Ferzan M. Ahmed, ODOT area engineer and project manager for the Worthington-Galena Bridge project.
Safety was another key concern as ODOT evaluated noise barrier materials. The agency particularly needed to minimize possible injuries and property damage caused if a car or truck collided with the noise barrier. PARAGLAS SOUNDSTOP GS CC sheet incorporates embedded polyamide filaments that hold the broken pieces of sheet in place in the event of vehicular impact. This prevents sheet fragments from falling from the bridges onto road and walkways below, thereby eliminating the need for self-containing safety netting.
"For us, one of the outstanding features of the PARAGLAS SOUNDSTOP GS CC sheet was its fragment retention," says Elvin Pinckney, environmental section chief for ODOT. "We really wanted a material that would not end up down on the street below if it suffered a car crash." In addition, studies show that the retention filaments are visually perceptible to birds, which deters them from colliding with the transparent noise barrier.
In addition to optimizing safety in the event of impact, ODOT needed a system that could reduce the risk of vehicles crashing into the noise barrier in the first place. To meet this project requirement, the agency chose to employ CYRO's patented cantilever system to install the noise barriers on both bridges. This proprietary system attaches to the concrete parapet and includes rigid vertical supports to position the noise barrier panels outside of the crash zone, or "Zone of Intrusion." This reduces the likelihood of a vehicle colliding with the noise barrier panels if it strikes the parapet during a minor crash, which serves to greatly reduce passenger injury and damage to the noise barrier.
General contracting firm Kokosing Construction Co. Inc., Fredericktown, Ohio, was charged with installing 10-foot-high and 12-foot-high transparent noise barriers running 150 feet along both sides of the Nordyke Road Bridge. The company was also responsible for setting up a 200-foot-long, 16-foot-high noise barrier on the northbound side of the Worthington-Galena Bridge. To facilitate both installation processes, CYRO provided critical on-site technical support.
"The help from CYRO's technical representative was very valuable," says Gary Obert, project engineer at Kokosing. "He helped us diagnose and address installation issues and also showed us how the fabricated frames and transparent panels fit together."
Colorless PARAGLAS SOUNDSTOP GS CC sheet panels were installed on the Nordyke Road Bridge, which did not having existing sound walls, in August 2006. For the Worthington-Galena Bridge project, ODOT removed the previous steel noise barrier and replaced it with the Smoky Brown tinted version of the transparent sheet to blend visually with existing brown metal noise barriers in the area. Installation for both projects was further facilitated by the light weight of the PARAGLAS SOUNDSTOP GS CC sheet, which made it easier to handle than conventional noise barrier materials.
Now that the noise barriers are in place, the suburban homeowners who live near the Worthington-Galena Bridge and noise-sensitive areas near the Nordyke Road Bridge are enjoying the quiet. With a sound transmission loss rating of 34 decibels (dBA), the 20-millimeter-thick PARAGLAS SOUNDSTOP GS CC sheet chosen by ODOT provided an appropriate Sound Transmission Coefficient (STC). This easily exceeds the Ohio specification stating that noise barrier materials have a minimum STC of 26 dBA.
In addition, the transparent material enables bridge travelers to enjoy views of the surrounding areas and avoid the "tunneling" effects caused by standard non-transparent materials, which cast passing vehicles in shadow.
Due to the success of the Worthington-Galena and Nordyke Road Bridge noise barriers, ODOT plans to use PARAGLAS SOUNDSTOP GS CC sheet again for several projects this year, including a noise barrier on the southbound side of the Worthington-Galena Bridge.
For this installation, the PARAGLAS SOUNDSTOP TL4 system will be used. This FHWA-approved system also utilizes PARAGLAS SOUNDSTOP GS CC sheet panels. During crash tests under NCHRP 350 Level 4 conditions, the PARAGLAS SOUNDSTOP TL4 system was able to considerably stabilize vehicles upon impact to reduce the severity of the crashes while protecting the noise barrier.
|Stephen D. Barratt is manager,engineered product sales at CYRO Industries, a wholly owned subsidiary of Degussa.|