You don’t need a sign to figure out where to enter the new Bechtler Museum of Modern Art, designed by Swiss architect Mario Botta and located in downtown Charlotte, N.C. A huge chunk of the building’s base appears to have been carved out of its east side, leaving a covered plaza that connects the street directly to the Bechtler’s central skylit atrium. “The idea was to build a public space, something personal and human scale, in contrast to the surrounding skyscrapers,” says Mario Botta Architetto project architect Tobia Botta, who works for his father.
Almost half of the museum’s 10,762-square-foot fourth-floor gallery is cantilevered over the entrance plaza, and the absence of windows in the austere, yet warm, terra-cotta façade only accentuates this deep opening. As in traditional museum and church architecture, the entrance proclaims itself; here, however, the grade does not change as the sidewalk plane slips through the plaza and into the lobby.
A single, 47-foot-tall column stands in the plaza, disrupting the play of pure solids and voids. It bulges in the middle, as if compressed by the weight of the gallery space atop it. (The center diameter measures 8 feet—double that of the column’s endpoints.) While the structural member itself is made of standard reinforced concrete, the tile cladding is mounted to a convex steel armature. This maneuver one-ups classical builders who used the technique of column entasis, or tapering, to subtly manipulate optical effects. But in contrast to the columns of the Basilica in Paestum, Italy, for example, which have massive capitals, Botta’s column meets floor and ceiling with minimalist delicacy.
“Sometimes, in architecture, you let the mystery prevail,” observes David Wagner, principal of Charlotte-based Wagner Murray Architects, the architect of record. (KingGuinn Associates, also located in Charlotte, provided structural engineering services.) Yet the column’s capacity is anything but ethereal. According to Wagner, its strength is rated at 12,000 psi, or two to 2.5 times greater than that of a standard column. Its 14-foot-6-inch-square footing lies hidden underground, below the basement level. And gravity is not the only stress acting here. The enormous overhang must resist potential wind loads from below (uplift) as well as from the side.
For all of its uniqueness, the swollen column does, in fact, belong to the building’s regular 29-foot-by-29-foot column grid—it’s just that all of the other columns are concealed within walls, and six of the 20 grid points are left empty. Could this massive external column have been left out, too? Tobia Botta and Wagner both confirm that they briefly considered this option. “We can all imagine a 90-foot cantilever in our dreams,” Wagner says, but the structure “would have [to have] been so massive as to significantly reduce usable space inside.”
Having accepted the necessity of the column, Mario Botta assigned it primary symbolic duties as well as load-bearing ones. “It’s not just something structural,” Tobia Botta says, “because we could have made it thinner. It has to represent the whole weight of the building.”