Two aging structures, the Earl C. Davis Memorial Bridge and Bridge No. 96, were deemed functionally obsolete and structurally deficient by the North Carolina Department of Transportation (NCDOT).
These bridges were the only access to and from Harkers Island. Despite attempts to extend the lifespans of each by replacing cored slab decking, jacketing concrete piling and more, the bridges had to be replaced.
Harkers Island sits south of Carteret County and is protected from the Atlantic Ocean by the barrier islands of the Shackleford Banks. The area receives major weather events, specifically hurricanes, so the project team created a bridge that could withstand powerful storms.
The Harkers Island Bridge Replacement project used non-ferrous reinforcing materials that increased the design life from 50 to 100 years and reduces future maintenance costs. The concrete piles and girders were reinforced with prestressed carbon-fiber reinforced polymer (CFRP) strands, and the cast-in-place substructure and superstructure utilized glass-fiber reinforced polymer (GFRP) bars.
NCDOT and Balfour Beatty used these materials because of their non-corrosiveness and ability to survive harsh coastal environments. Designed by NCDOT’s Structures Management Unit (SMU), the bridge is the first of its kind in North Carolina, and because of its success, it lands at No. 4 on our list of the year’s top bridge projects.
“NCDOT develops all of their structures, especially in coastal environments, to withstand major catastrophic events,” said William Janning, the project engineer at Balfour Beatty. “The steel-free design was also intended to account for the extreme and corrosive environment and an extended lifespan.”
Prior to construction, drone mapping was conducted of the limited space at the bridge approach. This allowed the team to map and plan logistics. The new structure was modeled in 3D, and onsite survey staff maintained tight tolerances.
NCDOT went through an extensive mapping process to identify the best option for the routing of the structure. A high-rise option was chosen to maintain boating traffic underneath.
Template structures were designed to drive the 100-foot-long, 24-inch square concrete piling at the designed batters. They were designed with maximum space for workers to move around while also providing the solid structure needed to maintain line and grade.
Stay in place pans were not used due to the need to maintain the ferrous free design. In its place, an under-bridge work platform was designed and constructed for the amount of stripping needed.
The project’s remote location led to challenges. The closest ready-mix concrete plant was 24 miles away, typically taking an hour to arrive onsite. That left only 30 minutes to test and completely pour out each concrete truck.
Crews worked through volatile weather and unpredictable storms during the summer. To ensure safety, weather alert broadcasts were used, in addition to stand downs and mandatory breaks.
Elevated pile driving templates presented a safety concern. To address this, the team created an in-house design for large, safe work platforms. The platforms included guardrails and worker tie-off connections.
The roadway’s realignment created the ability to convert Bridge No. 96 into a pedestrian bridge. The Straights Fishing Pier now also has a parking area, which is another plus for the community.
Project: Harkers Island Bridge Replacement
Location: Harkers Island, N.C.
Owners: North Carolian Department of Transportation
Designer: NCDOT Structures Management Unit
Contractor: Balfour Beatty Infrastructure, Inc.
Cost: $60 Million
Length: 0.853 Miles
