Design flexibility without compromising on energy performance
Curved glass allows designers to make a statement with new construction or retrofits that stand out from the square edges and flat surfaces that make up most facades.
When creating a building, architects might be constrained by the building materials they work with.
Fortunately, when it comes to glass facades and particularly curved glass, those constraints are now beginning to ease. For the last two decades, advances have been made in terms of production processes and glass types, offering tighter radii, increased widths, and larger overall dimensions.
Design creativity can be unleashed in the form of new surfaces, contours and shapes, including conical, spherical and free-form 3D, while corners and edges can be softened into curves.
What remains largely unchanged is the decisive influence of the glass supplier’s expertise in production; when it comes to making curved exterior glass, process control is everything.
While larger furnaces have been introduced to cater for increases in scale and bending machinery has been enhanced, matching the performance of the latest flat glazing can be a challenge. If mastered, the rewards for architects and building users alike are significant.
"To meet the latest building energy regulations, you need to use complex, coated types of glass, these coatings are mechanically and chemically sensitive, so it’s difficult to bend them without damage or losses in terms of yield. It means that bending modern architectural coated glass has become a serious specialization - not everybody can do it."
Tamás Kovács, European Technical Services Manager at Guardian Glass
A plate of glass is laid over or inside a curved mould, into which it gradually sinks by gravity alone after being heated to around 1100°F (600°C).
1. The flat glass is placed on the mould
2. The glass is heated up to around 1100°F (600°C)
3. The glass sinks by gravity and takes the shape of the mould
4. The curved glass slowly cools down
This prevents both roller wave distortion and anisotropy, and although tempered, or safety glass cannot be used, laminates can be added to provide safety features. However, it remains a time-consuming process, and coatings must withstand a longer heating period.
An alternative is to bend the glass during heat treatment in a furnace, which either fully tempers or heat-strengthens the glass at the same time. The process is similar to the tempering or heat-strengthening process, the only difference being the presence of a flexible area in the tempering furnace. It is far quicker than the gravity bending process, but it raises the challenge of potential optical distortions, typically created during the heating or rapid quenching/cooling stages. In addition, only concave and cylindrical shapes can be produced when certain coatings are used.
Insulating Glass Units (IGUs) can be cold bent by mechanically capturing an otherwise flat panel within a bent frame or, in close coordination with a structural silicone sealant supplier, structurally bonding the panel to the outside face of the frame.
When the flat panel is forced into an out-of-plane state, the resulting stresses diminish the capacity remaining to resist wind and other service loads. Heat-treated glass is commonly selected for cold bent applications in order to help compensate for this reduction. Nonetheless, cold bending is generally only utilized for mildly out-of-plane geometries, such as those with radii greater than 120 inches (3 meters). Glass, sealant and framing manufacturers should review and approve each application.
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The challenge: Harmonize and blend six heritage townhouses with a new, six-story tower above.
The solution: The sinuous, six-story tower incorporates low-iron bent glass with a white pattern to flow above the heritage buildings that make up its podium, providing a stunning accompaniment to the existing façades.
Benefits of curved glass: The curved, white and clear glass curtain wall affords unobstructed views for occupants in the new addition, while making a statement in its upscale neighborhood.
Curved glass performance: The high-performance coatings help meet energy performance criteria, while ceramic frit further lowers solar heat gain. The project was built to LEED Gold certification standards.
The challenge: Create an acoustically advanced concert hall, which is one of the largest in the world, with a facade that evolves according to weather and environment, yet permits the required elegance the project demanded.
The solution: state-of-the-art 3D techniques to shape curved glass. The curved glass panels are in some cases carved open to transform a straightforward façade, into an enormous quartz crystal.
Benefits of curved glass: The surprising facade changes as it catches the reflections of the sky, the water and the city. Vault-shaped openings offer spectacular, theatrical views of the River Elbe and downtown Hamburg.
Curved glass performance: The high-performance coating maintained its functionality during the 3D shaping process to meet the required energy performance and aesthetics.
The challenge: Create a building inspired by the famous Lansetti II vase while meeting the required solar protection and thermal insulation.
The curvature had to meet very precise measurements, while the glass had to deliver clean color and high transparency.
The solution: a double skin façade allowed the architect to create a beautiful sculptural form that performs functionally and architecturally.
Benefits of curved glass: More than 5,000 single and double-curved panels and tapering panels in low-iron glass allowed the creation of a building with no straight lines
The development of high-performance coated glass has helped to improve the solar control, the thermal insulation and the acoustic properties of glass, but until not so long ago, the problem was keeping the aesthetic and energy performance quality of the coated glass when bending it. Recent advances in the glass coating technology allow now to achieve a complex curved shaped facade which helps make a building more energy efficient and more comfortable to work or live in.