Project Overview
Traffic in suburban Chicago is often heavy, with scores of commuters traversing the region’s roadways each day. Approximately 20 miles southwest of downtown Chicago, the Mile Long Bridge on the Central Tri-State Tollway (I-294) is a critical piece of infrastructure in the Chicagoland area that supports the travel of 150,000 vehicles per day. In a multi-year project that began in 2019, the Illinois Tollway, in partnership with contractors FH Paschen of Chicago and Walsh Construction, as well as County Prestress & Precast, LLC of Janesville, Wisconsin, replaced two aging bridges to accommodate increasing traffic demands, minimize maintenance, and improve safety. The project came to fruition through the production and installation of more than 500 precast, prestressed concrete bridge beams.
Exceptional Value, Exceptional Service Life
Project leaders were challenged with replacing the existing four-lane northbound and southbound bridges with wider structures to accommodate five lanes of traffic and a Flex Lane in each direction. Precast, prestressed concrete bridge beams offered the optimal solution to achieve the owner’s goals, which included minimal disturbance to the environment along with reduced maintenance and an extended service life.
A unique beam design, inspired by the California wide-flange beam shape, was developed specifically for the Mile Long Bridge Project. County Prestress & Precast, LLC manufactured 523 precast concrete girders ranging in length from 127 to 187 feet and weighing up to 125 tons. Measuring 90 inches deep, the beams incorporate 48 high-strength steel strands and 10 ksi compressive-strength concrete, making them the longest prestressed concrete bridge girders ever fabricated, transported and erected in the Midwest.
Even so, getting the girders to the project site was a challenge. To address potential transportation challenges, the team conducted industry outreach in the early stages of the project and used the PGStable module within the Bridgelink program to analyze lateral stability during erection and transportation. This analysis guided equipment requirements and set critical criteria for transportation, such as wind speed, truck speed, superelevation of roadway and minimum turning radius, ensuring a safe and efficient delivery process for the beam transport. The massive beams were hauled to the area on specialized trailers, with each load requiring four personal escort vehicles and two state patrol cars used to supervise the transport of each load. Once the girders were delivered to the jobsite, contractors used an innovative gantry system to install the precast concrete girders near the waterways. This technique helped allow four lanes of traffic in each direction to remain open throughout construction, mitigating potential headaches for commuters.
Site logistics were further complicated by the presence of two major railroads, three water resources, local roads, and a series of commercial properties beneath the Mile Long Bridge. This required unique design considerations and construction approaches. To minimize disturbance to the aquatic ecosystem near the project site and reduce the project’s impact on transportation and commercial activities, LHQ Tri-State Partners – a joint venture of Lochner , HDR and Quigg Engineering)– developed a solution that reduced the number of piers used on the original bridges from 53 each down to 26 piers per bridge—a substantial design improvement from the original bridges. The Illinois Tollway was able to reduce the number of spans to 27, of which 22 are prestressed, by nearly doubling the length of the beams. This reduction in the number of spans also reduced the number of deck joints, enhancing bridge durability and reducing long-term maintenance and future inspection demands. Additionally, the construction schedule was meticulously carried out in three phases to help minimize road closures and avoid traffic congestion.
The use of precast concrete on the Mile Long Bridge Project provides myriad benefits to all parties. In addition to its high-performance strength across long spans, precast concrete was the building material of choice for its low life-cycle cost and unmatched durability in the harsh winter weather typically experienced in the Chicago metropolitan area. The completed bridge boasts an expected service life of 100 years, an additional lane of traffic, and an unmatched resiliency that will support motorists in the region for the next century.
The keys to successful delivery of such a large and challenging project like this was to initially understand the site constraints, establish priorities, clearly define the design criteria and keep close and constant communication and collaboration among all the project partners and impacted stakeholders throughout planning and design development.
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013. |