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Smithsonian Channel 'How Did They Build That' Pier 55
Little Island at Pier 55 is an urban marvel. Perched above the Hudson River on a bed of precast concrete flowers, this floating park offers a new open space for New York City locals and tourists to revel in nature and the artistry of its makers.
The initial goal of this project was to address costly maintenance of decaying steel and timber piles on the Hudson River while also creating a new 2.4 acre park space. The solution had to be durable, and it had to be striking enough to warrant a spot on New York City’s famed waterway.
“The owners were very sensitive to the durability issue,” says David Farnsworth, principal at Arup, the engineer on the project. “That is why we settled on precast concrete as the material of choice for this project.”
The project stakeholders knew precast concrete would provide a resilient structure that could withstand the brackish conditions of the Hudson River. But they didn’t want just another flat pier with a park on top. It had to be special.
Originally, the owner envisioned the park as floating carpet with an undulating platform of precast concrete that hovered over the river. But the team quickly determined that the initial vision wasn’t economically or structurally feasible.
After several iterations, the design eventually evolved into a series of blooming tulip shapes that emerge from slender precast concrete stems of varying heights that act as piles in the river. Each stem is topped with a massive precast concrete flower, and together these flowers provide the base and structure of the park. “Some of the pots are 2000 ft2, others are 100 ft2,” Farnsworth says. The design allowed for consistent loads across the piles while still delivering the undulating surface and compelling profile.
Milled Styrofoam petals
Farnsworth’s team worked closely with the precast concrete producer, the Fort Miller Co., to figure out the best and most efficient way to create the stems, pots, and petals to deliver the design. “The collaboration felt like a private partnership,” says Joe O’Malley, sales engineer at Fort Miller. “It pushed us beyond limits that we didn’t think we could achieve.”
Initially, the team imagined building each flower as a single unit, but the size and weight of the finished products would have been too unwieldy to create and ship. Therefore, they broke the design into 132 pots of varying sizes and depths, topped by four to six distinct precast concrete petals, and four to six precast concrete topping planks. The assembled pots would be clustered together on top of the stems in a Cairo pentagon tiling pattern.
“The overriding challenge of this project was the complex geometry of the pots,” Farnsworth says. Execution of the fabrication and erection required a tremendous amount of coordination and effort.
Each of the 655 unique petals and column heads was first developed by the architect and engineer using scripts and three-dimensional (3-D) modeling. The precast concrete producer then used digital scripting to pull data from the models for shop drawings, reinforcing bar fabrication, and form fabrication. These models were uploaded to a five-axis computer numerical controlled milling machine to mill a negative shape of each petal out of a foam material that could support the weight and pressure of the wet concrete. To ensure proper geometry, the precast concrete producer either dry-fitted or 3-D scanned 40 of the 132 completed pots in the manufacturing facility.
“It was an innovative solution to a complicated problem that has spawned a whole new line of business for us,” O’Malley says.
Once the precast concrete pieces were created, Fort Miller shipped them via flatbed truck to a river port, where each pot was assembled using welded stainless steel connection plates. The heaviest pot weighed roughly 88 tons. The pots were then shipped four at a time via barge 120 miles to the project site, where they were installed over the precast concrete piles, which had already been driven into the riverbed. This carefully timed delivery minimized the needs for laydown space on the jobsite, which was located just a few feet from the busy Hudson River Greenway walking path.
From afar, the park appears to have bloomed out of the water atop a giant field of flowers. Visitors to the park can enjoy green space, flowerbeds, walking trails, and a waterside amphitheater. “We feel grateful to have been a part of this project,” O’Malley says. “There is nothing else like it in the world.”