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Retired Bonner Bridge Used for Research

Wednesday, September 29, 2021

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After being dismantled a few years ago, the Herbert C. Bonner Bridge will now be used for research by engineers studying how to build better bridges for the future.

For the research, the North Carolina Department of Transportation is partnering with North Carolina State University in Raleigh. The Department has already sent girders from the retired bridge, which are slated to undergo stress testing at the university’s Constructed Facilities Lab.

The goal of the research project will involve taking the lessons learned about how an aged bridge exposed to a half-century of extreme weather conditions can inform better bridge designs in the future.

“This is a very unique opportunity,” said Neil Mastin, who manages NCDOT’s Research and Development unit. “It’s not often you get a bridge in that extreme environment for nearly 60 years that was intact enough that we can actually use it for testing.”

North Carolina Department of Transportation

After being dismantled a few years ago, the Herbert C. Bonner Bridge will now be used for research by engineers studying how to build better bridges for the future.

According to reports, the testing of the girders will consist of two parts. To start, the girders will first be subjected to low-level cyclic loading where a force is applied, removed, and reapplied repeatedly in a manner similar to the passing of vehicles over a bridge.

Following the load tests, the bridge girders were subjected to monotonic loading until reaching peak load levels, which involves applying force to the structure until it breaks. In early testing, the university reported that it took more than 200,000 pounds to break the girder—or the total you’d get from stacking two and a half tractor trailers on top of each other on just one wheel.

For the monotonic loading, sensors with cameras were used to observe how the beam responds to loads, how it moves and where cracks form when pressure is added to the girder.

“What we're trying to really investigate is the amount of pre-stressing in this structure,” said NCSU Assistant Professor Giorgio T. Proestos, who is leading the project at the university. “Is it enough? Should there be more? Should there be less? And how does that pre-stressing change in 60 years? Based on the results of the experiment, there might be changes in the way things are done moving forward.”

NCDOT is funding the project and facilitated the work to salvage the girders and test them in Raleigh. The Department is slated to publish the study’s results once the project has concluded. Mastin adds that the results of this project will likely inform bridge design and building decisions nationally, not just in North Carolina.

Bonner Bridge Replacement History

The Herbert C. Bonner Bridge replacement project (later known as the Marc Basnight Bridge) approval was first announced in August 2015, after various legal obstacles from environmental groups halted construction. At the time, the project was reported to begin in the spring of 2016.

Built in 1963, the bridge has served thousands of vehicles over nearly six decades, suffered boat and barge collisions and battled harsh ocean elements and intense currents that, at times, almost caused it to lose its footing.

Former Gov. Pat McCrory indicated the terms of a settlement agreement reached in June had been met, and the environmental groups represented by the Southern Environmental Law Center—which included the Defenders of Wildlife and the National Wildlife Refuge Association—had dropped all remaining lawsuits that stood in the way of construction.

During building efforts in 2017, however, crews working on the new Herbert C. Bonner Bridge drove a steel casing into the three underground transmission cables that bring power to Hattteras and Ocracoke Islands, causing damage to two of the three cables, according to the Cape Hatteras Electric Cooperative. Because of the incident, more than 7,600 homes and businesses were affected, according to The Virginian-Pilot.

Only a few days after the incident, the contractor responsible was sued by residents in a court action filed before power even returned in many communities.

By May 2018, the firm responsible for the power outage incident, PCL Construction (Denver), reached a $10.3 million settlement with local businesses and residents. Breaking the agreement down, the firm will pay $8.1 million to businesses and $2.25 million to residents and renters in the area affected by widespread blackouts and evacuations that lasted nearly a week after the outage.

The settlement was ordered by U.S. District Court Judge James C. Dever III.

To reach maximum efficiency, the bridge was divided into five regions and consisted of three or four 54-inch diameter vertical concrete cylinder piles, transition and long navigational spans that used a combination of cast-in-place reinforced concrete pile caps with six to 30, 36-inch square concrete piles in a battered configuration to further resist wind and ship impacts.

In total, work on the project, which opened to traffic on Feb. 25, used 690 piles measuring over 15 miles in length combined.

In June 2019, Deep Foundations Institute (Hawthorne, New Jersey) announced the $252 million, 2.8-mile Marc Basnight Bridge was the recipient of its 2019 DFI Outstanding Project Award.

The Basnight Bridge team consisted of engineering company HDR, general and foundation contractor PCL Civil Constructors, and owners the North Carolina Department of Transportation. The team is slated to be presented with the award at the DFI 44th Annual Conference on Deep Foundations Oct. 15-18, in Chicago.

The new bridge is expected to have a 100-year service life.

By September, the NCDOT had reportedly extracted 374 of 1,619 piles and removed 46 of 187 spans. In total, 70,000 tons of debris were expected to be removed and unloaded offshore where portions would be used at four different existing artificial reefs.

In order to remove these piles and spans—some piles reaching 6 feet in diameter and 130 feet long—the crews used a special machine with a 6-foot saw blade to make an initial gap. The endeavor also implemented a hydraulic-powered blade.

According to Pablo Hernandez, resident engineer for NCDOT, the hydraulic-powered machine doesn’t actually spin the blade, nor does it have teeth like a saw. Instead, the machine pushes through concrete and steel, similar to a slow-moving, horizontal guillotine. The technique is reportedly safer for the high areas over the water.

Once a section is cut free from the bridge, a crane outfitted with a giant fork then removes the concrete portion and places it on a barge for offshore hauling. This is allegedly the toughest part of the dismantling process, as large hoses are also used to jet water into the bottom and around the columns to remove sand, while the large cranes gradually lift them.

The deconstruction project was expected to be complete by early 2020 with 1,000 feet remaining at the south end of the bridge as a walkway and possibly a fishing pier, depending on federal permits.

By July of that year, 44 loads were reported to have gone to the reefs out of 75 loads that were estimated to complete the project. For the first six months, the barges were able to take the Inlet, completing about 27 loads on the original route.


Tagged categories: Bridges; Bridges; Colleges and Universities; Department of Transportation (DOT); Girder; Infrastructure; NA; North America; Quality Control; Research and development; Testing + Evaluation; Transportation

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