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SWEET SUCCESS

Gate Precast turns to 3D-printed forms for ‘sugar crystal’ façade

A towering mixed-use structure with a unique façade in Brooklyn’s Williamsburg neighborhood has not only changed the New York City skyline, but has shown the transformative possibilities of 3D-printed concrete formwork. Thanks to a collaboration with the U.S. Department of Energy’s (DOE) Oak Ridge National Laboratory in Tennessee, Jacksonville, Fla.-based Gate Precast Co. was able to bring the intricate design of One South First’s “sugar crystal” exterior to life as well as provide a major step forward for architectural precast.

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The modern One South First and its interlocking Ten Grand Street office tower provide 360-degree panoramic views of Manhattan and Brooklyn. One South First features 332 apartment units and Ten Grand Street has 18 office floor suites. The mixed-use building also features 13,000 square feet of ground-floor retail space. PHOTO: Gate Precast Co.
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A co-developer of Big Area Additive Manufacturing, the Department of Energy’s Oak Ridge National Laboratory used the system at its Manufacturing Demonstration Facility in Knoxville, Tenn., to print the initial 3D forms for One South First’s precast window panels.
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PHOTOS: Oak Ridge National Laboratory
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PHOTO: Autodesk
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Gate Precast used 3D-printed molds by Oak Ridge National Laboratory and Additive Engineering Solutions to rapidly manufacture nearly 1,600 window panels in varying shapes and sizes for the iconic One South First building. Some of the molds were turned upside down to create different window shapes, which allowed for additional cost and time savings. PHOTOS: Gate Precast Co.
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Designed by Manhattan-based COOKFOX Architects, the 45-story building sits on the edge of the East River and features interlocking towers that seamlessly integrate residential, retail, and office spaces together. One South First is located at the northern end of developer Two Trees Management Co.’s redevelopment plan of the Domino Sugar refinery site, and is the third project to open after mixed-use 325 Kent (2017) and the six-acre Domino Park (2018). Future plans include the adaptive reuse of the landmarked Domino Refinery for creative office space and two new mixed-use residential buildings.

One South First’s contemporary façade design was inspired by sugar’s crystalline structure, a nod to the site’s industrial history. “With crisp modernist repetition, angled white precast concrete creates a deep, faceted façade, generating a play of light and shadow to animate the rigorous forms,” notes COOKFOX Architects. Moreover, the panels were designed to self-shade. “Each elevation is formed to respond to its specific solar orientation and optimized to reduce energy use for cooling,” explains the architectural studio.

However, the varying profiles of the nearly 1,600 window panels required for the project would mean a lot of formwork. In fact, Gate Precast’s experience with precast systems led COOKFOX Architects to approach the producer due to the level and variety of finishes desired for One South First. Utilizing conventional wood molds would take significant time on an already tight construction schedule, and Gate Precast would most likely need to hire subcontractors to keep up with the production required—driving up costs. Enter 3D printing.

ROOTED IN RESEARCH

When Gate Precast received the contract for One South First’s façade, the company was already involved with an enclosure research project between the Oak Ridge National Laboratory and the Precast/Prestressed Concrete Institute, of which nine-plant Gate Precast is a key member. The project looked at how 3D-printed molds could help with the labor shortage of skilled craftsmen, as well as reduce forming costs, shorten lead times and improve durability.

“Oak Ridge National Laboratory is well-known for its R&D work in 3D-printing capabilities,” as Diana E. Hun, subprogram manager for Building Envelopes at ORNL, noted in a PCI Journal Project Spotlight. “During some interactions with PCI, we found out that the precast industry is short on certain types of skilled labor, which led us to think about opportunities for 3D printing in that industry.”

During the first year of the research project, ORNL tested the concept with a cornice from an elaborate façade of a Nordstrom project Gate Precast was pursuing in New York City. Using large-scale additive manufacturing/3D printing and computer numerical control (CNC) routers, a form was produced for a 1-ft. wide segment. Gate Precast successfully cast 40 concrete pieces without degradation to the mold at its Ashland City, Tenn. plant. For the following year, ORNL was looking to scale-up the concept, which is when Gate Precast proposed the One South First project. This allowed the 3D-form printing process to progress from concept to commercialization in under two years.

Oak Ridge researchers saw the building as the perfect platform to demonstrate that Big Area Additive Manufacturing (BAAM) technology could rapidly manufacture molds suitable for architectural precast. ORNL collaborated with Gate Precast and PCI to design and produce the forms out of carbon fiber reinforced acrylonitrile butadiene styrene (ABS), a common thermoplastic compounded with a 20-percent mixture of chopped carbon fibers.

“The carbon fibers help improve the strength by two times and stiffness by four times of the molds, relative to the ABS plastic, allowing the inserts to support the weight of the poured concrete and the force of the demolding operations over repeated cycles,” explains ORNL’s Brian Post, the project’s advanced manufacturing engineer.

Once ORNL researchers developed the process science to reliably manufacture the molds, Additive Engineering Solutions (AES) of Akron, Ohio, a BAAM machine user, was brought on to help with production due to the laboratory’s limited capabilities. AES’ machine, which produced 17 of the Gate Precast forms (ORNL produced 20), outputs up to 80 lb. per hour in sizes up to 12 x 5.5. x 6 ft.

The 3D-printed molds begin with computer-aided design (CAD) models, which are sliced layer by layer to develop toolpaths that drive the printhead. The printer then executes these toolpaths layer by layer by extruding molten polymer to form the final part. After the molds were printed, which took between eight to 11 hours, they were machined to their final dimensions with a five-axis CNC router—roughly another eight-hour process. Subsequently, the forms were shipped to Gate Precast’s Winchester, Ky. plant, which handled the lion’s share of the One South First tower elements. A sister operation in Oxford, N.C. tackled fabrication of the Ten Grand Street order with conventional formwork.

CONTINUOUS COLLABORATION

COOKFOX Architects worked closely with Gate Precast and owner Two Trees, who served as general contractor on the project, throughout the 3D manufacturing process. This allowed for full-scale mockups of the forms to be created, reviewed and tweaked early on. Both COOKFOX and Gate shared an individual BIM model in Autodesk’s Revit software, which allowed for constant dialogue and real-time modification of the panels. “We went through several iterations of the variation in panels with Gate’s input,” Pam Campbell, partner at the architectural studio and member of the project team, told PCI’s Ascent magazine. “We looked at how the façade would be panelized and how many modules would be ganged together at each run of façade, based on the crane capacity and transportation limitations. We arrived at a balance that retained the amount of patterning and visual variation in the façade while accommodating the optimized panelization of the modules.”

With the finalized 3D-printed forms, Gate was able to manufacture 150 to 200 castings on them—significantly more repetitions than a wood or fiberglass mold, which can only be used about a dozen times. Steve Schweitzer, vice president of Operations for Gate Precast, explained the manufacturing process of the panels in an Autodesk project video, “[We] would start with putting in the reinforcing rebar, the hardware, connection hardware, bearing hardware, window inserts. Once all that is set, then we pour[ed] our concrete into the mold. It usually set for about 10 to 14 hours to cure. Once it’s cured, the next morning, we strip[ped] the piece out. The piece is carried out into our finishing area, where we tilt it up. That’s where we acid-wash it first, and then we polish[ed] the front face. Once that’s completed, then we move it into storage, and eventually, it gets moved into the window-installation area, where they install the windows and caulk prior to being shipped to the jobsite.”

The producer made 993 window panels for the residential portion of the building at its Winchester plant and 612 panels for the commercial/retail portion at its Oxford facility. To further mimic the sugar aesthetic COOKFOX envisioned for the façade, Gate utilized a bright white, sand-rich mix. The pre-installed windows streamlined the installation of the façade, shaving off nine months from the construction timeline.

Gate isn’t keeping the technology behind the One South First project’s success a secret. The producer went into the partnership with ORNL to develop a new technology for the industry as a whole. According to Mo Wright, Gate’s marketing director, “all of the information and practices developed during the research was shared with PCI.”