It used to be the case that glass could not bear structural loads. Although its high silicon content makes it a very strong material, the slightest overstepping of glass's low elastic deformation limit results in breakage. This is due to the absence of a crystalline structure, a deficiency to which glass owes its transparency but which also results in a lack of internal cohesion. When a crack develops, the material can't cope.
New production processes can increase the material's strength, while developments in lamination that enable it to be used as a structural material are also growing. The combination of toughened glass and lamination produces strong and thin glass sheets, which are particularly used in frameless glass façades. Other possibilities include glass columns and fins for glass façades. This has led to many new buildings in recent years employing glass structurally.
A good example of this is Herzog & de Meuron's 40 Bond Street project in New York. The ten-storey residential building is in the city's NoHo district and comprises five duplex townhouses and 23 apartments above. The architects placed the structure of the building in the façade, leaving the interior free of columns. The glass curtain walls follow the grid of the floor-to-ceiling window bays and feature a cast-glass relief that wraps over the slab and column structure. The curved panels, which were manufactured in Barcelona, form a continuation of the window panes, but they express the load-bearing structure behind them. According to the architects, the window panes and the curved glass panels 'dissolve in a play of translucency, light and reflection'. It's this interplay that makes the building so alluring.
Other strategies of building with glass take this approach of seemingly load-bearing glass even further and hide the real load-bearing structures altogether. Such strategies are visible in the Toledo Glass Museum by SANAA and Villa 1 in Bennekom by Canadian practice Powerhouse. In both buildings, the façades are fully glazed by frameless windows. The load-bearing structural cores are hidden in closed volumes in the interior, from which the roof cantilevers. The glass façades seem to carry the roof, but in fact they're suspended between window frames hidden in the ceiling and floor.
In Villa 1 the glass façade runs along the perimeter, giving the impression of a floating roof, while diagonal bracings are hidden in the ceilings. In the case of the Toledo Glass Museum, the façades feature double, parallel-running, gently curving sheets of glass with a 1m cavity between them. The building structure is hidden above the ceiling in a single interior volume that contains a solid plate providing lateral bracing. The façades feature 3,000m² of gently curving float glass, originating from Austria but curved and laminated in China.
Japanese architects favour glass structures as thin as air. In his Kanagawa Institute of Technology, Junya Ishigami employed 305 slender steel columns, scattered around in a seemingly random fashion. The white columns and the frameless glass façade almost make the building disappear. The façades are formed by 5m×1.5m glass panels that are just 10mm thick. They are stabilised by perpendicular fins, which offer complete transparency. Ishigami says he wanted to replicate 'the expanse of a starry night sky or an astronomy map; both have undetermined borders'.
A more conventional use of glass fins can be found at the EWHA University building in Seoul. Dominique Perrault turned the brief for the building into an undulating landscape. A wide pedestrian path with stairs cuts right through the landscape, recalling, according to Perrault, 'the Champs Élysées or the Campidiglio in Rome.' The glass walls on either side of the path afford views into the large buildings under the grass roofs. The façades have wide fins, suggesting solidity when viewed obliquely, yet keeping views highly transparent.
Glass also lends itself to a completely different kind of architecture. Sometimes, it is applied in a decorative fashion without making use of a cutting-edge structural design. The Health Department in Bilbao by Coll-Barreu is a good example. The building, with façades entirely made of glass, occupies the corner of a closed block of buildings.
At first glance, the faceted façades seem innovative, but the structure is actually quite straightforward. The whimsical design of the glass conceals an orthogonal support structure, which features more or less straight walls. The space in between serves to circulate air and adds to the sound insulation and fire safety of the building. In addition, the façade is, according to Coll-Barreu, a 'social vehicle', because the façade reflects the 'dynamic urban life' inside the building.
The Mahler 4 office tower in Amsterdam by Erick van Egeraat also applies glass in a decorative way, but in this case it's screen-printed glass that enhances the architectural design of the building. The lower half of the building features slanted glass façades that are printed to resemble ice floes. The façade of the top half of the tower is clad with panels comprising a layer of black gravel applied to a fibreglass-reinforced polyester laminate. According to the architects, "the nub of the idea is a rock on ice." Whatever you think of it, Van Egeraat created an expressive landmark in the middle of a set of bland, corporate office towers.
Another recent project featuring printed glass is Elephant House at Copenhagen Zoo. Foster + Partners designed two glass-topped domes that appear to rise out of the earth. The glass panels forming the domes are covered in what seem to be random scatterings of white leaves. These are, in fact, computer-generated leaf patterns creating shadows throughout the enclosures, giving the elephants the possibility of staying out of the sun.
The architects created the fritting pattern on the glazed roof canopies by sampling four species of trees. The leaf patterns are rotated and scaled and randomly populate the roof, so that no two leaves are the same. The overlapping patterns provide dappled light.
One of the principal qualities of glass is its apparent absence. This has led many architects to attempt to design a building that visually disappears into the background. They rarely succeed though, as glass is reflective and has a greenish hue due to the small quantities of iron oxide it contains, therefore always giving away its presence.
Glass is a building material, for want of anything better. In a factory cafeteria in an office park in Ditzingen, Barkow Leibinger designed an imposing, CNC-sawed laminated timber roof. They wanted the exterior to be kept as transparent as possible, underscoring the visual predominance of the roof. So they applied glass in the façades. "We would have used no façade at all, but we are not quite there technology-wise," explains the practice.
If we do ever get there, glass will have finally redeemed its promise of complete disappearance, thereby making itself redundant as a building material.