The new Bonner Bridge replacement recently received several 2020 Design Awards from the Precast/Prestressed Concrete Institute’s annual contest, including the “Special Awards: Sustainable Design” honor, as well as “Best Main Span Bridge More Than 150 Feet” in the Transportation Awards category.
Judges awarded 25 projects and five honorable mentions for design excellence in building and transportation categories. The PCI Design Awards, now in its 57th year, showcase the creative and innovative use of precast and pre-stressed concrete in a variety of applications.
“Once again, the precast, pre-stressed concrete industry has put its best foot forward and has delivered many inspiring and impressive projects,” said PCI President and CEO Bob Risser, P.E.
“Each year, the PCI Design Awards program demonstrates that precast, prestressed concrete is not only a practical solution to many construction challenges, but also a head-turning aesthetic solution.”
A panel of industry experts that includes precast concrete producers, engineers, and architects judges all nominees.
The buildings and transportation categories are judged on aesthetic, structural, and use versatility; site, energy and operational efficiency, and risk reduction; and resiliency, such as structure durability, multi-hazard protection, and life safety and health.
The new $252 million, 2.8-mile-long Marc Basnight Bridge spans Oregon Inlet, one of the most dangerous channels on the Atlantic Coast, due to its treacherous currents, constantly shifting depths, and high winds.
The conditions meant the original 130-ft-wide steel girder span had to be dredged continuously to preserve the required 14-ft channel depth, and it was rapidly reaching its end of life. That bridge acted as a lifeline for residents of North Carolina’s barrier islands, which meant its replacement had to be reliable and extremely durable.
“Providing the required 100-year service life for a bridge subject to that extremely harsh saltwater environment was a major challenge,” says Domenic Coletti, principal bridge engineer for HDR, the lead design firm for the project. His team tackled this requirement through the extensive use of precast concrete, providing a high quality, economical, resilient and low-maintenance structure that can resist 84 ft of erosion, hurricane-level winds, and impacts by the occasional passing ship.
The decision to use precast concrete occurred early in the pre-bid engineering phase, when the design-build team recognized the many benefits this material leant to the project design. Using precast concrete improved quality and durability while reducing costs and shortening project timelines, Coletti says. It also minimized disruption to the environmentally vulnerable barrier islands, and it lessened the risk of impact of construction on the area’s 20 legally protected species, which include manatees, bald eagles, Peregrine falcons, and five species of turtles.
The precast concrete design also helped to address one of the biggest challenges faced on this project: location. “The project site is remote, with limited access for material delivery,” Coletti says. “And the working conditions in the Oregon Inlet were subject to very fast currents, high winds and surf, storms, nor’easters, and hurricanes—making fieldwork difficult.”
The 2.8-mile-long replacement bridge features the third-longest continuous segmental box-girder superstructure in North America, with 11 spans at lengths up to 350 ft. The 44 approach spans use virtually identical precast concrete bent caps and cylinder piles, and the bridge’s foundation consists of 669 precast concrete piles, totaling over 12 miles.
To ensure durability in the extremely harsh environment, the piles’ final depths are up to 140 ft below the seabed. This depth accommodates anticipated scour (seafloor erosion), which is expected to remove as much as 84 ft of the seabed, while still providing sufficient embedment into the seafloor to maintain stability and strength.
Visit pci.org for details and photos of all winning and honorable mention projects.