Ultra-high-performance concrete (UHPC) helped The Atrium, a seven-story building in Victoria, BC, Canada, achieve a dramatic and cost-effective façade in its first use in a precast concrete exterior cladding system in North America. The UHPC allowed the panels to be light enough to be hung from a unitized curtainwall envelope system and thin enough to allow an air-displacement ventilation system to fit within the exterior-wall thickness. The panels also helped reduce structural requirements to resist seismic forces.
The 204,000 ft2(19,000 m2) building, located in a historic downtown neighborhood, features ground-floor shops and a seven-story central atrium that introduces daylight into the heart of the building. The building was designed as a high-density, mid-rise form to fit into its environs, using a palette of natural and durable materials.
The UHPC panels were cast with a surface pattern of vertical lines cast from a mold that was hand-carved by the architect. Just 3/4 in. (19 mm) thick, the textured spandrel panels used minimal fiber-reinforced-polymer bars in the perimeter ribs as a safety precaution against accidental overloading. By eliminating reinforcing bars in the panels, it was possible to create thin, complex, curved precast concrete panels.
The panels also provide superior durability, thanks to an extremely dense matrix. Consequently, the building’s maintenance requirements are greatly diminished because the UHPC panels are much less susceptible to the absorption of environmental debris. About 690 panels were produced from curved and flat molds using a displacement-casting process. The panels are ¾ in. (19 mm) thick with 1.18 in. (30 mm) ribs, making each light, strong, and thin. The façade design used rectangular panels that are straight, curved, and a combination of both. All of the panels were 51 in. (1.3 m) high and varied in width from 30 in. to 85 in. (800 mm to 2.2 m), with a mode of 51 in.