Reed & Reed Inc. Implements First Slide-In Bridge Construction in New Hampshire
New Granite State Bridge Pulled in Place: New Hampshire DOT Employs Slide-In Bridge Construction Technology for the First Time on an Ossipee Bridge Replacement
The New Hampshire Department of Transportation (NHDOT) recently passed a major milestone in the state’s transportation construction history when it employed Slide-In Bridge Construction (SIBC) to replace a deteriorated bridge in rural Ossipee. It was the first time the Granite State has utilized this process, a type of Accelerated Bridge Construction (ABC) that has been used successfully in many other states including Maine, Massachusetts, and Vermont.
Woolwich, Maine, contractor Reed & Reed Inc. performed the SIBC procedure on the 64-year-old Bearcamp River Relief Bridge located on Route 16, a principal highway traversing the White Mountains National Forest. Reed & Reed’s $16.9 million contract with NHDOT includes replacing three red-listed bridges – Bearcamp River, Bearcamp River Relief, and Lovell River.
While Reed & Reed is building the three bridges, subcontractor A.J. Coleman is performing the earthwork for reconstructing 3.4 miles of Route 16 as part of the contract. The Albany, New Hampshire, contractor is reclaiming, grading, and paving the roadway beginning from the Lovell River Bridge and extending north to the Chocorua River Bridge in West Ossipee. This work is taking place with alternating one-way traffic through the work area. Traffic is being controlled using flaggers, operational signs, cones, and barrels.
Key project personnel for NHDOT’s Construction Bureau are Project Manager Jennifer E. Reczek, P.E., and Contract Administrator Chuck Flanders, while Domenic Cyr and Ted Clark are Reed & Reed’s Co-Project Managers, with Greg Letourneau serving as Project Superintendent.
Two Replacements to Slide In Place
In the SIBC process, a new bridge superstructure (deck and beams) is built on temporary supports, usually parallel to an existing bridge that continues to carry traffic. After new abutments and piers have been constructed and the new bridge superstructure is completed, the road is temporarily closed. The existing structure is demolished or removed, and the new bridge is positioned (“slid”) into place on the new permanent supports.
According to NHDOT, the two companion bridges on NH Route 16 in Ossipee were built in 1955 and both are slated for SIBC replacement. One bridge spans the Bearcamp River, the other spans the Bearcamp River flood plain, providing relief.
Bearcamp River Relief, a four-span I-beam concrete bridge, was the first bridge to undergo slide-in construction. Measuring 168 feet long and 28 feet wide, its deck was in poor condition and it had a sufficiency rating of just 11.4 percent.
Bearcamp River is the longest of the three bridges, with a five-span I-beam concrete structure measuring 392 feet long and 28 feet wide. It is scheduled for slide-in construction in 2020. The bridge’s deck and superstructure are in poor condition, earning it a sufficiency rating of 40.6 percent.
The Lovell River Bridge is the oldest and shortest of the three. Built in 1950, it is a single-span I-beam concrete bridge with a length and width of 58 feet and 31 feet, respectively. It has a sufficiency rating of only 32.4 percent. The new bridge is being built using conventional construction – the road will be closed, traffic detoured, the old bridge demolished, and the new bridge constructed.
875 Tons of Concrete and Steel
The new Bearcamp River Relief bridge has a length of approximately 168 feet and a width of 37 feet. It consists of two 12-foot travel lanes, two 5-foot shoulders, an 8-inch concrete deck, a barrier membrane, and a roadway pavement of 1-inch bituminous concrete roadway base course and a 1-1/2-inch surface course. T3 steel bridge rails and 2-foot-wide, raised brush concrete curbs are also part of the deck structure. Five welded steel plate girder bridge beams with 30-inch deep web depths underlie the deck. This completes the major components of the superstructure. The contractor built the new structure adjacent to the existing bridge on temporary support bents.
Constructing the temporary support system for the new bridge was itself a significant effort. H-Pile “A” frames had to be driven to refusal at about 200 feet. Adjacent A frames were joined together with diagonal steel bracing, and capped with a pair of horizontal W24x104 steel shapes. Half-inch steel plates braced the caps. This completed the temporary structural supports. Workers welded channel steel to the top of the steel caps, providing a roller channel for heavy duty Hillman rollers during the planned slide-in.
Stantec, the project consultants, designed the bridge move assuming the new superstructure’s dead- and live-service loads to be 400kips at each abutment and 950kips at the single pier, for a total service weight of 1.75 million pounds, or 875 tons. And this massive structure had to be moved sideways about 52 feet without cracking the deck. This called for very powerful and sensitive equipment and highly detailed procedures.
During this time, Reed & Reed had also built the new abutments and the single pier near the existing bridge. To support these structures, the contractor had driven 24-inch and 30-inch pipe piles up to 200 feet to bedrock. Most of this work was completed while traffic continued on the old bridge.
A Slow Roll
The slide-in demolition and replacement of the Bearcamp River Relief Bridge was set for an 84-hour window early in fall 2019. Beginning Friday, September 27 at 6 p.m., NH Route 16 was closed to all traffic at the Bearcamp River area. Crews began demolishing the old bridge while others set up the sliding mechanism for moving the new superstructure.
The sliding mechanism consisted of a 14x176 pull beam mounted over the Hillman rollers and a 1-3/4-inch threaded pull rod attached to a 100-ton center-hole hydraulic jack.
This equipment was set up at both abutments and the pier.
A number of jacks were required to lift the new structure off its temporary supports and placed on the sliding mechanism. Next, three 100-ton pull jacks were used to slide the structure over to the new abutments and pier. This 52-foot move was performed in 8-inch increments. At this point, the structure was again jacked up to allow the removal of the sliding mechanism and replacement of temporary bridge bearings with permanent ones. And lastly, the bridge was lowered to its permanent berth.
Beating the Clock
Reed & Reed completed all necessary additional work to allow opening traffic to the new bridge. The scheduled target time for bridge and roadway to re-open was Tuesday, October 1st at 6 a.m. But it actually re-opened on Monday, September 30, at 6 p.m. – 12 hours early. The entire slide-in replacement of an 875-ton bridge was accomplished in just 72 hours. NHDOT intends to use the experience gained in this slide-in bridge construction project to reduce construction impacts and costs in future, even busier, locations.