Project Overview
In the Pacific Northwest, a new industrial park located on 310 acres in Tacoma, Wash., promises to help local businesses “connect faster” and “think bigger.” The park, dubbed FRED310, is centrally located and offers more than 600,000 ft2 of space to interested firms. Operating such a large industrial park efficiently requires optimum access to the location. To that end, part of the development process for FRED310 included construction of an underpass to provide public road access beneath an existing spur railroad track. To bring the 151-ft-long bridge to life, Concrete Technology Corporation and project engineering firm Kimley-Horn partnered with Rainier Rail on a precast concrete solution using accelerated bridge construction (ABC) techniques.
Minimal Disruption, Maximum Value
For more than a decade, ABC techniques have increased in popularity, primarily due to their ability to expedite installation while minimizing closures. Precast concrete is generally the material of choice for such projects, as was the case for the 192nd Street overpass project at FRED310. According to Conner Doolan, structures engineer for Kimley-Horn, both precast, prestressed concrete box beam and steel deck plate girder superstructure options were evaluated. Although the two options had similar projected construction costs, Rainier Rail chose precast concrete because of its low maintenance requirements, long-term resilience, and ability to counteract the project’s challenges. Additionally, precast concrete eliminated the need for temporary shoofly tracks, resulting in cost savings.
A primary concern for the project team was reducing disruptions to the railroad, making the deployment of ABC methods essential. Following the completion of the underpass’s foundations, which were constructed under active rail service using strategically placed piles that straddled the track, the precast concrete caps and superstructure were erected as part of a planned multiday service outage. For the bent caps, reinforcement from the pile extensions was inserted into corrugated blockouts in the caps and then grouted. At the abutments, smaller-diameter reinforcement cages extended from the bottom of each precast concrete cap into corrugated blockouts in the pile tops, which were also grouted to ensure structural continuity. Precast concrete also streamlined installation of ancillary features of the underpass: wingwalls, handrails, and cover plates were efficiently integrated using cast-in anchor bolts in the abutment caps and threaded inserts in the beams, enhancing construction speed and overall quality.
Customized design elements, including nonstandard spans, tailored beam sections, and bespoke abutments, all helped address the project site’s complex constraints. These included a requirement to avoid obstructions in the roadway median, the presence of overhead transmission lines, and the curved alignment of the track. The result was a nonstandard bridge layout with short end spans and a long interior span of 89 ft. The irregular span configuration meant typical industry-standard details could not be used, requiring innovative structural solutions. The unequal span lengths imposed high torsional demands on the bent caps, which were specially designed to accommodate these forces. Additionally, the precast concrete abutments featured tapered backwalls to account for the curvature of the track, allowing the bridge ends to align perpendicularly to the track and maintain proper rail geometry.
Using precast concrete brought additional advantages to the work. High-performance materials and optimized prestressing— including permanent, temporary, and debonded strands—enhanced structural efficiency and durability. Modular detailing of structural components will facilitate future maintenance, with elements including individual beams, wingwalls, handrail panels, and cover plates all designed for straightforward removal and replacement. This increases resilience by enabling future repairs and upgrades to take place with little to no disruption to operations. In addition, construction-related traffic disruptions and associated emissions were reduced thanks to the shorter ABC timeline, limiting the project’s carbon footprint. The result is a 151-ft-long, three-span bridge structure that will help spur the region’s business activity.
“Precast concrete allowed us to complete major bridge work during a single seven-day rail outage while delivering a modular and long-lasting structure with minimal maintenance needs,” Doolan says. “The underpass improves safety for the community by removing the need for a rail crossing and supports local growth by enabling the expansion of the FRED310 industrial park.”
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013. |