Beyond the curve
Due to channel glass’ versatile shape, it can do more than form a simple curve. The glazing can serve as a tall, sweeping façade that encloses interior rooms, transitions between straight and curved sections, and integrates windows. While the design freedom the material provides can push the form and shape of modern buildings, it is important to consider how the geometry of these complex curves can impact the design and specification process.
Tall curves
As is the case with all vertical channel glass systems, the cast-glass channels in curved systems can span up to 7 m (23 ft) without interim framing if allowed by a building’s design-imposed wind loads. When working to extend the elevation, either for aesthetics or to combat wind load constraints, it is important to note wind load anchors are not compatible with the system. The irregular geometries created between the nested channel glass segments as they curve prevents the anchor from running between the planks and attaching to structural elements behind the glass.
To extend the curved channel glass elevation, it is necessary to use stacked joints. Stacked joints use a structural member to split the elevation into two separate openings, which are then individually framed in an aluminum perimeter frame. They allow design teams to elicit the effect of tall, continuous spans of glazing while ensuring a structurally stable system. A case in point is the Oceanaire Seafood Room in Houston, designed by GHA Architecture. The design team specified a three-tiered channel glass system that stretches approximately 10.7 m (35 ft) high and curves around the corner of the restaurant.
Unusual transition conditions
When achieving tight radii or working with unusual transition conditions, such as straight-to-curved sections, it can prove challenging to align channel glass segments within the geometrical constraints. To achieve the appropriate configuration, the design team can use a combination of different standardly available channel widths, ranging from 232 to 331 mm (9.13 to 13.03 in.), with consistent flange depths.
In the case of the University of San Francisco John Lo Schiavo Center for Science and Innovation, designed by NBBJ, unusual transition conditions were necessary for the cast-glass channels to animate and follow the curve of the building’s adjacent walkway. To account for these transitions, the design used a combination of raked and curved channel glass heads and sills. This effectively made the size and positioning of each channel glass piece unique, allowing the façade to transition between curved and straight sections. In some instances, the linear glass channels step around architectural elements that intersect the walls at unusual angles.
Integral vision lites
Where desirable to incorporate integral vision lites or other glazed systems in curved channel glass systems, it is often necessary for the window manufacturer and supplier’s in-house engineering team to work together to overcome design-specific challenges. With appropriate design and specification, this custom condition can contrast with the channel glass’ translucent form to add movement to the façade, extend line of sight, or enhance daylight transfer.
For example, in the University of Virginia’s Claude Moore Medical Education Building, the design team and supplier worked together to create a multi-story, curved façade with integral vision lites that wraps around lecture rooms. The two parties coordinated to eliminate the normal need for structural isolation between the channel glass system and adjacent window systems, as well as the jamb framing at those locations. From a design and performance standpoint, this reduced sightlines from framing to allow more natural light to stream into the space for students and faculty.
