March 16, 2023

NORTH CAROLINA - North Carolina DOT and construction giant Balfour Beatty are working together to replace Harker's Island Bridges, both more than 50 years old, with a modern two- lane bridge. The older version, a swing bridge, has become increasingly difficult to repair with costs rising rapidly. The new bridge will have a 45-ft.-high rise, adequate for commercial fishing boats and pleasure craft. The island borders the Atlantic and is a popular spot for fishermen, tourists and vacationers.

The project is about 45 percent complete. It is slated to cost $60 million and will be finished in the fall of 2025. The new bridge will be composed of two 12-ft. lanes each with a 4-ft. shoulder.

The ocean side location of Harker's Island draws many visitors. However, the beauty has a downside. The salty, sea air and spray has a corrosive effect on construction materials. So, NCDOT looked for construction alternatives.

"There will be almost no ferrous materials in the bridge; we are using carbon fiber in the tensioning strands and fiberglass reinforcing in many of the bridge elements," said Brad McMannen, NCDOT resident engineer. "The bridge supports and the bridge deck use these elements and will be more resistant to corrosion than traditional steel rebar. We are expecting the bridge to have a life span of 75 years."

The old bridge, which touches down on a small island as well as Harker's Island, will be demolished when the new bridge is complete. A second existing bridge connecting the mainland to the straights fishing pier will be preserved and converted to a pedestrian bridge for fisherman, pedestrians and tourists. Car traffic will not be allowed on the pedestrian bridge.

The new bridge will have a 3,200-ft. length with a main span over the navigable boating channel of 164 ft. supported by 78-in. Florida I-Beams (FIBs); 72-in. and 54-in. FIBs also were used on the project in the approaching spans. The average daily traffic on the bridge is 3,350 vehicles, with the traffic increasing in the summer.

"The new Harker's Island Bridge will be an important structure," said McMannen. "Traffic will be able to proceed from the island directly to the mainland with no interruptions. This is especially important during the summer and in case of hurricanes or weather issues."

Environmental Concerns

A major obstacle for the contractor was that the waters surrounding the bridge are a fish spawning area with environmental regulations preventing construction in the water from April 1 through Sept. 30. This "fish moratorium" period short circuits the entire construction season in most states.

Balfour Beatty has approached the problem with creativity and a tight grip on the schedule.

"We started the work of driving piles the first day we were allowed," said Pete Distefano, project manager of Balfour Beatty. "Since we had only until March 30 of that year to perform pile driving, we started immediately running night shifts as well as day. We were in a race to get as many piles driven as possible. In the first year we drove 135 permanent concrete piles, which included all the foundations from the mainland out to the navigable boating channel."

The work crews used an ICE Model I-62 diesel impact hammer for the pile driving. The piles were 24-ft. square and were driven about 75 ft. into the ground to support the bridge. The longest pile was 130 ft.

The old bridge was quite narrow and the waterway shallow. So, using barges as a construction platform was ruled out. Instead, to support construction Balfour Beatty built a temporary work bridge adjacent to the new structure designed to hold fully loaded 275-ton crawler cranes. The work bridge is supported by 30-ft. steel pipe piles, which also had to be installed before the moratorium stopped driving operations. The temporary work bridge was about a half mile long.

The only metal in the bridge is the stainless-steel anchor bolts, girder sole plates and the steel reinforcing in the bridge barrier rail.

Engineers from North Carolina State University have been heavily involved in studying the design elements of the unique bridge and have placed monitors at various points to test how it sustains the stresses from traffic.

"I'm not sure if there is another bridge like this in the entire world," said Distefano. "We have had a great deal of challenges with this unique design, but we also have had the best team imaginable for building this bridge, including both Balfour Beatty and NCDOT crew members. There is no way we would be where we are with the project today without this incredible team." CEG

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