Ennead Architects with Leslie E. Robertson Associates
Completed in 2010, the New Gateway Center has brought a central hub to Westchester Community College that stands out two years later as a model use of customized prefabrication. The $33 million, 70,000-square-foot, three-story building provided a place to welcome students of this commuter school and expanded the institution’s overburdened facilities, adding classrooms, offices, language and computer labs, and an auditorium. Ennead Architects based their design around the idea of the threshold, developing a concept of welcoming and arrival that, in architectural terms, would sit lightly on the college’s beautifully landscaped campus. The firm laid out the facility’s functional spaces in two academic wings that embrace a landscaped courtyard. The project’s centerpiece is a 48-foot-tall transparent glass pavilion that connects the wings on two levels and serves as the lobby and welcome center. It was here that the architects, working in collaboration with structural engineering firm Leslie E. Robertson Associates (LERA), developed a unique architecturally exposed structural steel system that supports the pavilion’s glass curtain wall while allowing copious amounts of daylight to flood the space.
The foremost challenge in designing a customized structural solution for the pavilion was cost. “We knew we had to think about how to create this central gateway in a manner that would be both inventive and modular,” explained Ennead design partner Susan Rodriguez.
This led the team to the idea of using prefabricated structural modules that could be quickly and easily erected on-site, bringing a high level of design to the project without sending the budget through the roof. “We were looking for a material that could sponsor something special but on its own would be simple in conception. Like a soldier, it becomes different when you bring many together,” said Dan Sesil of LERA. “We wanted to create a building block that lent itself more to manufacturing. So you could get this fairly simple conception and build it into something extraordinary.”
The result of the team’s hard work is a system of 233 architecturally exposed structural steel boxes stacked one atop the other to form a spindly, trellised grid that supports the pavilion’s glass volume. Built up from 4-inch channels and 1-inch plate, the boxes each measure 8 feet 11 1⁄8 inches long by 4 feet 7 1/4 inches high by 3 feet deep. R&S Steel prefabricated the boxes in their shop in Rome, New York, and then trucked them to the campus with a temporary internal bracing element that kept them from deforming during shipping and installation. Once on-site, ironworkers got down to the business of stacking the boxes and connecting them. Almost all connections were made with shims and 7⁄8-inch-diameter type A325 bolts, cutting down erection time by limiting the amount of field welding necessary. Steel plate tabs welded to the boxes in the shop form the curtain wall connections.
The pavilion also features an architecturally exposed structural steel stair and bridge that connects the second floors of the two wings across the airy, daylit space. Both the stair and bridge are built up from 1 3/4-inch-by-12-inch structural steel stringer plates and channels. Laminated glass panels make up the treads and floor. Two steel hanger rods support the bridge at mid-span, connecting to the main stringers with custom pin and jaw fittings designed by LERA.
Structural Steel Fabrication
The two academic wings are also framed with structural steel, though there the structure is more conventional wide-flange post-and-beam construction with concrete on metal deck flooring. The exception to this standardized affair is that the third floor cantilevers out over its base on all sides from 6 to 30 feet, reinforcing the “sitting lightly upon the land” theme of the building. The most significant of these cantilevers are on the east and west ends of the structure. The east features the largest cantilever. Supported by four trusses on the roof made up of wide flange sections that range from W14x120 to W14x283 with double angle diagonals that range in size from 2L6x4x1/2 to 2L8x6x1, the volume projects more than 30 feet out over the grass below. The trusses also form parapet walls that disguise the roof’s mechanical array.
The original design included a cantilever on the west end that extended 40 feet, but it was lost to value engineering. Instead, the projecting volume is supported by an architecturally exposed structural steel inverted tripod element that reduces the cantilever to 24 feet. Each leg of the tripod consists of two parallel 1 1/4-inch-by-7 1/2-inch structural steel plates stitched together at regular intervals with a 3-inch-diameter round spacer bars, creating ladder-like elements. To eliminate bending forces in the tripod, each leg terminates in a steel pin detail. At the base, a plate assembly designed to transmit gravity and lateral forces to the foundation below ties the 4-inch-diameter pins together.
Perhaps fearing that new students might have trouble locating the college’s New Gateway, the design team anchored the south wing of the building with a 60-foot-tall spire. Clad with zinc panels, the spire tapers from 10 feet wide at the base to less than 3 feet wide at the top, like an exaggeratedly tall A-frame house. It consists of two interconnected 1-inch structural steel plates built up into an 18-inch overall cross-section. A full-height LED array runs up the east face of the tower, creating a beacon that shines both day and night.