In the world of solid waste management, the organizations that achieve high levels of energy efficiency are getting a lot of attention and fanfare. When the Solid Waste Authority of West Palm Beach made plans to build a state-of-the-art, energy-efficient, waste-to-energy system, they decided to include an education center with an elevated pedestrian bridge that would allow curious citizens to visit the new facility.
However, designers of the bridge faced a tight construction schedule that had to be coordinated with construction of the adjacent boiler building and cooling towers to ensure the crane would have needed access for the bridge assembly. “There was only a small window of opportunity to install the bridge components onsite,” says William Maples, structural engineer for CDM Smith. The team considered several alternative materials to meet the owner’s cost, timing, and durability goals. “It was decided that precast concrete elements were the only way to meet all of the design criteria,” he says.
The final design features a precast concrete column and double-tee design featuring Y-shaped columns to support the 7 feet (2.1 meters) walkway. During the design process, CDM Smith worked closely with Charlie Baker the precast concrete producer specialty engineer, Dura-Stress, to come up with the precast concrete column design, which enabled them to minimize the number of piers needed to accommodate the underlying roadway, parking lot, and extensive underground utilities. The columns are all self-supporting for lateral stability and could be assembled in a short window on-site. “Dura-Stress provided outstanding final structural design for the superstructure and coordinated with the CDM Smith foundations,” Maples says.
Spanning between them is the walk surface made from high performance double-tees with a double-tee roof on top. “The low-profile long spans and the flaring piers open to the sky, which is why we chose the name Sky Bridge,” he says.
By choosing precast concrete and working closely with the precast concrete producer, the designers were able to deliver an attractive, high-performance bridge that helps make the new facility a showplace for visitors. “The finished structure is stunning,” Maples says. “The CDM Smith design team blended the education center with the energy complex, creating a smooth transition with the sky bridge.”