Architectural precast and structural precast concrete structures can do more to reduce your project’s carbon footprint, give you more green performance and lower costs. More than mere tweaks, these five proven techniques can help you make sure you’re getting the most out of precast concrete on your next sustainable construction project.
Location: Chicago, Ill.
Type of Precast: Architectural precast and CarbonCast® Insulated Wall Panels
Size: 417,000 square feet (55,247 square feet of architectural precast)
CarbonCast panels made under an agreement with AltusGroup, Inc.Glittering Vertical Campus Is Adorned with Architectural Precast
When Roosevelt University, already a prominent downtown Chicago, Illinois higher-education institution since 1945, saw the need to expand its existing main campus facility it quite literally moved up. Firmly committed to its "Loop" location, the University took the only 17,500 square feet available and turned normally horizontally organized facilities skyward in the new Wabash Building.
At 32 stories, Wabash is the tallest academic building in the US after the University of Pittsburgh’s Cathedral of Learning. The vertical campus encloses academic, institutional, recreational, and residential spaces in a first-of-its-kind design. "The building is designed to be iconic, to attract new students, yet to fit with and honor its surroundings," says Jeff Hrubec, senior vice president for Chicago-based VOA Associates, the project design firm.
The bold design statement clearly denotes a new image for Roosevelt, and also creates a scintillating backdrop to the famous Louis Sullivan-designed, Romanesque Revival Auditorium Building, which has been home to the University since 1945. Connecting in four places, the $110 million Wabash Building allows more breathing room in the Auditorium Building, much needed large and lecture size classrooms, office space, and a new home for the Real Estate School and College of Business.
Due to the relationship of the small site and the required 415,000 square feet of program, the design team offset Wabash’s core, expressing it in architectural precast on the north façade. In homage to Louis Kahn’s servant-served concept, this approach allowed maximum possible spans for large, uninterrupted gathering spaces in the lower floors of the tower. The building is one of the few Chicago skyscrapers with LEED Gold Certification.
The tiered northern elevation is a study in massing as well as integration of form and materials. It suggests the development of the students it houses, moving from a blank slate at the base, through a series of elegantly coffered panels, to the top where punch windows provide views of the northern lakefront expanse.
"The architectural precast is a spine for the building, chosen as a solid mass for the glassy, prism box," says Hrubec. Enclosing the elevators and other functional spaces, the cladding gradates upward from a dark gray at the base. The coloring pays homage to the Auditorium Building and its very dark granite topped by light granite.
In planning the 150-year building, the design team chose architectural precast due to its longevity and its design versatility using different finish opportunities. "Architectural precast was the strongest option from a performance standpoint," says Hrubec. He notes that masonry wasn’t an option due to the building’s height, and that the team had talked about metal panels early on, but was concerned about fading and oil-canning over time.
With a new project planned immediately to the north, the precast provides a fire-rated system with standard-looking reveal panels on the first five floors, with no windows. The panels meet the parapet lines of the Fine Arts Building Annex, a historic structure whose façade was preserved as part of the project. The Annex façade remains on its original foundation, separated from the precast by a two-inch expansion joint.
Above, and set back to recognize the historic roof line, the next 11 floors are clad with precast panels that are coffered to accommodate penetrations while maintaining a uniform look across the façade. "The precast gave us an artful disguise for exhaust footprints," says Hrubec. "A lot of thought went into how it was formed. High Concrete added flares to the formwork, and blocked out the openings. We made several trips to their factory to see how it was manufactured, and to understand its constructability and finish options."
The top tier is a 16-story façade that presents a checkerboard of glass and concrete, as though the coffered "eyes" of the middle tier have been opened. The windows provide daylighting for residential spaces located at the top of the tower.
Due to the location of the core, and the need for insulation, the team chose CarbonCast insulated panels that sandwich two inches of rigid XPS foam for an R-10. The wythes of the panels are joined with high-strength C-GRID carbon fiber connectors. "It was a team exercise between VOA, Power Construction, and High Concrete to figure out the detail of these panels," says Hrubec.
Working on the tight urban site, VOA, Power, and High Concrete also had a high degree of interaction on construction sequencing and timing. The team rented a 40’ section of an adjacent parking lot for panel erection. Where the lower level touches an interior property line where another building will be, more steel was used. The precast panels there are load bearing down to grade.
CarbonCast is a registered trademark of AltusGroup, Inc.
C-GRID is a registered trademark of Chomarat N.A.
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