Dingle Ridge Road Bridge Replacement over I-84
The first bridge replacement on the New York interstate to use the “slide-in” approach to accelerated bridge construction (ABC) was designed with precast concrete beams to replace twin bridges in two weekends, with the longest road closure only 20 hours. Beams for the $10.2-million project, located on Dingle Ridge Road over I-84 in Southeast, New York, were fabricated and trucked to the site for assembly next to the existing bridges before sliding them into place on tracks.
This ABC approach was used for a number of reasons, says Bala Sivakumar, vice president and lead designer at HNTB, the design firm. The original steel bridges were too narrow for either to provide suitable two-way traffic, especially with a large elevation difference between them. A temporary bridge between the bridges was rejected because it would take two years to construct, add $2 million to the budget, and impact the sensitive environment. “This approach kept traffic delays to only one night,” he says. “This was a very good choice for this site.”
The new bridge consists of an 80-foot center span and two 30-foot end spans, which served as temporary approach spans during the slide. Once the slides were completed, flowable fill was to be placed beneath them and supported by wing walls, making them ground-supported slabs. “It made the slide go faster to treat them as temporary spans,” Sivakumar explains.
The precast concrete New England Extreme Tee (NEXT) beams (featuring a larger flange to speed construction) were fabricated by Dailey Precast at its Shaftsbury, Vermont plant. The beams used for the Dingle Ridge Road slide were typical NEXT beams except for stainless-steel plates cast into the end diaphragms. The plates, 7 feet long by 1’2” wide, were polished to a mirror finish to reduce the friction coefficient, creating a smooth sliding surface, explains Jared Steller, quality-control manager at Dailey Precast.
“Tolerances were very tight for the shoes, and careful handling was needed to ensure they retained their finish,” he says. “This bridge process was new to us, but casting the beams followed the same procedures as always, with a few minor adjustments in the details.”
The precast concrete components were delivered to the site and assembled adjacent to the existing structures. The slides were done on two successive Saturday nights, with the existing bridges demolished earlier in the evening. The new bridges then were slid into place using a track to guide the stainless-steel shoes.
General contractor Yonkers Contracting Company worked closely with Marino Crane (the slide-in contractor), and Seifert Associates (the construction engineers) to plan the slide. The contractor also talked with other companies with experience in this technique.
“The biggest challenge was the pace of the project’s schedule from bid until the bridges had to be ready to slide,” says Tom Whelahan, Yonkers project manager. Less than nine months elapsed from receiving the award of contract until the bridges were slid into place in September 2013.
Yonkers drove piles to bedrock over the sliding route to prevent settling of the heavy loads during the transport. Additional supports were needed to overcome a 16% grade slope on the underpassing street to ensure the bridges—which required about 2 million pounds to be temporarily supported during the move—to slide on a level track system.
Additional time was needed to raise both approaches by 2 feet to accommodate the required clearance beneath the bridge. The first bridge slid into place in about 10 hours, owing to initial discrepancies in the jack strokes, which caused some racking, along with a torrential downpour. “The rain required us to maintain close inspection of the shoes to ensure support from the slide bearings was maintained,” Whelahan explains. The second bridge was slid into place under dry conditions in less than four hours.
The resulting bridges were installed and ready for use in less than 20 hours from the start of the bridge closure in both cases. “NYDOT felt that they saved an entire construction season while eliminating costs and modified traffic patterns on the interstate,” says Whelahan. “This approach saved money and time minimizing hazards to the traveling public associated with typical staged highway construction.”