Engineering Chicago's Next Architectural Jewel
Last month, construction crews from Northbrook, Ill.-based curtain wall contractor Arcadia Products began the monumental task of assembling what will certainly become one of the most unusual building façades along Chicago's famed Michigan Avenue.
Approximately 720 panes of insulated glass in 250 different shapes are being pieced together to form a jewel-like face for the new $55 million home of the Spertus Institute of Jewish Studies.
When completed this spring, the 10-story façade will sparkle like a crystal, offering passersby vivid reflections of the city around them, including Grant Park across the street, as well as glimpses into the inner workings of one of the city's most prominent Jewish education and cultural centers.
Each of the 36 facets is being carefully positioned to provide calculated and meaningful reflections of the surrounding urban environment. Adjacent facets, for example, lean in opposite directions (one upward, the other downward) to mirror the sky and the ground side by side. Some facets will offer calming reflections of the trees in Grant Park and others will mirror the hustle and bustle of Michigan Avenue.
“We designed the façade so that the unique reflections from one piece to the next will be consistent within each facet, and you'll be able to feel that they are in plane with each other,” says Timothy Tracey, associate principal with Krueck & Sexton, Chicago, design architect for the 155,000-sf facility. The firm collaborated with building envelope engineer Advanced Structures Inc. and curtain wall consultant Shepphird Associates (both based in Los Angeles) on the 161-foot-tall, 80-foot-wide glass exterior.
Tracey says the key to creating crisp and consistent reflections was designing each facet to remain as flat as possible. “We did not want glass that rippled or bowed,” he says. “We want the glass to remain flat and straight so that the faces stay true to each other and the reflections don't start melding into each other.” To accomplish this, the team specified an outer layer of glass that Tracey says is a little thicker than what would typically be required for this application.
The custom, 1.375-inch-thick insulated glass unit from Viracon, Owatonna, Minn., features an extra-thick outer lite (0.375 inch), backed by a ½ inch of air space and two ¼-inch interior lites that are laminated together. The interior surface of the outer lite is layered with a low-e coating and a 40% ceramic frit pattern to help control solar heat gain along the east-facing exterior.
To further accent the crisp, clean angles of the façade, the team designed a minimal structural system. The four-sided structurally glazed system offers unobstructed views of the glass; no mullions or metal framing will protrude on the exterior side of the wall. Instead, each glass lite will be bonded with high-strength, high-performance silicone sealant to aluminum frames and then clipped every four feet to vertical aluminum extrusions that extend 14 feet on floors one through eight and 21 feet on the top two floors.
“It's a sophisticated system that relies on the silicone for its integrity back to the metal framing,” says Tracey. “The thin vertical aluminum extrusions essentially work as the window frame for the glass.”
Supporting each vertical aluminum frame member is a series of Y-shaped mullions that have been custom designed with a radial piece to accommodate the numerous angles of the glass exterior.
“The spherical shape at the head of the mullion allows the same mullion with the same radius bend to be used across the entire wall system,” says Tracey. “It also allowed us to develop a connection back to that mullion that is always true to the glass surface.”
Keeping the weather out was a top concern, especially given the façade's minimal structure, says Tracey. The only components keeping the exterior weather-tight and free from moisture intrusion are the insulated glass units themselves and a 1¼-inch silicone joint between each panel of glass.
To ensure that the glass wall would stand up to the pounding winds off Lake Michigan, the team commissioned Carrollton, Texas-based Construction Consulting Laboratory to build and test a two-story mock-up that included multiple facets to mimic the design for the Spertus facility. The test system was subjected to a wind pressure of 47 pounds per square foot and a wind speed of 136 mph. It passed without any leaks, and CCL gave the team the green light.