Precast Concrete NEXT Beams Speed Construction After Hurricane’s Rampage
Precast concrete NEXT beams were used to speed construction on the #84 Bridge on Route 105 in Brighton, Vermont, after Hurricane Irene’s rampage in August 2011 caused the existing structure to fail. With no viable detours, the bridge was scheduled to be closed for only 21 days while the new bridge, complete with precast concrete abutments, wing walls and approach slabs, was constructed. The contractor received a bonus for completing the construction three days early.
“This was a rural area, so the traffic counts weren’t high, but there were few options for detours,” says Kristin Higgins, project manager for the Accelerated Bridge Program at the Vermont Agency of Transportation. “We wanted to create a prefab bridge that could be lifted into place quickly to ensure we minimized disruptions to traffic.”
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The NEXT Beam offers stems that are wider than those on standard double-tee beams, accommodating higher design loads. PCINE developed the girder to speed construction when adjacent box beams in the 45-ft- to 90-ft-span range might be used. The one-span Brighton Bridge features four 71-foot-long, 28-inch-deep NEXT beams.
Abutments and wing walls also were designed with precast concrete to ensure ease of construction. “Casting and erecting the NEXT beams was easy,” Higgins says. “The abutments and wing walls were more challenging.” The abutments were match-cast as two 20-foot, 34-ton pieces, which were then post-tensioned. They feature multiple 2-foot-diameter galvanized, corrugated steel pipes so they could be mounted on supporting piles. Power lines ran close to the final line of piles, so the piles were moved slightly to accommodate the utilities.
The abutments are flanked on each side by two10-foot, 11-ton wing walls connected by splice sleeves. Four 20- by 7-foot approach slabs slope up to the main span on each end of the bridge. “We worked closely with the precaster to ensure all of the details would be easy for them to construct,” she says.
Two cranes, one on each side of the bridge, were used to set the 52-ton girders into place. Headed bars were cast into the 10,000-psi girders and protruded from the shear keys, with high-performance concrete used for the closure pour of about 9 inches between beams. The outside beams also feature a precast curb with embeds for connection to the guardrail.
The project was the second of two structures completed in Vermont during the 2013 construction season to feature NEXT beams. An earlier one, Route 125’s #23 Bridge in Hancock, remained open during construction via a temporary bridge. That access allowed designers to complete it first to see if any issues arose that could then be applied to the Brighton project, where speed was much more critical. For more details on the Hancock project, see the related case history.
“The 71-foot length was a little longer than we needed for Brighton, but we decided that the time saved by not redesigning was worth it,” says Higgins. “It allowed us to go beyond the minimum length needed, which we liked.”
VTrans used NEXT beams on several projects earlier, Higgins notes, and she expects to see them become more prevalent. “We’re starting to use them a lot more often, especially due to hydraulics issues and our desire to keep the beams above the flood waters as much as possible. Up to 70 feet or so, you really can’t beat NEXT beams.”
The project came in under budget, at less than $1 million, and it met its schedule. “We were really surprised by the cost, and that’s a good sign for future use of the beams.” Indeed, the state has two more bridge replacements planned for summer 2014 using NEXT beams.
All the precast components were manufactured by J.P. Carrara & Sons, Inc. of Middlebury, Vermont.
