Glass at the cutting edge - Glass used in building design

Architectural Review, The, August, 2001 by Susan Dawson

These systems can be used in overhead glazing and can be faceted to suit curved forms. The headquarters of Cellular Operations, Swindon, UK, designed in 2000 by Richard Hywel Evans, is a 9m high glass vault which curves like a ribcage over two floors of open-plan office space and tapers at one end to a bull-nose. The facade is formed of glass panes faceted at different angles, some differing in angle at all four of their edges. They are fixed to specially designed castings with Planar adjustable bolts, a modification of the standard system.

Until recently, structural glass bolted systems were limited by the amount of deflection which was deemed acceptable by structural engineers. Schlaich Bergermann's Kempinsky Hotel [1] in Munich broke this spell. The glass entrance wall is composed of l.5m sq panes attached at their corners to a cablenet structure so delicate as to be almost invisible, yet flexible enough to move up to a metre under wind load. A new arts complex in Philadelphia, US, by Rafael Vinoly and structural engineer Dewhurst Macfarlane, takes this idea one stage further in the search for ultimate transparency; the centre has a glass roof enclosed at its ends by a glass curtain suspended only from vertical cables.

Glass as loadbearing structure

We think of glass as a delicate material which must be framed or bolted in place on a building. It is - in theory - as strong as steel but whereas steel, when stressed, will yield, glass contains flaws which cause it to fracture under stress. In the past the answer was to design glass to very low stresses, but as structural engineers and architects began to understand its characteristics more fully, and as methods of laminating became more sophisticated, the idea of a glass loadbearing wall became an irresistible temptation.

The entrance canopy to KP Foods at Billingham, Teeside (architect Studio BAAD, structural engineer Techniker), is a wing-like glass canopy supported at each end by three glass panels, arranged in a Y-shape on plan to give support and lateral stability. Each panel is 2.1 m high and consists of two panes of toughened glass laminated together; the canopy rests on stainless steel fins UV-bonded into the 3mm laminate between the panes.

A system of laminated glass beams and glass columns using mortice and tenon joints at the junctions of beam and column was developed by structural engineer Dewhurst Macfarlane and Design Antenna (AR August 1995) to create a glass entrance foyer to - appropriately - a Glass museum in Dudley, UK. The glass elements required an almost incredible precision in manufacture - joints between glass roof panels had to meet along a glass beam only 30mm wide.

In 1995 Macfarlane was asked to produce ideas for a 10m cantilevered glass canopy for a plaza in the Tokyo International Forum, Japan, designed by Rafael Vinoly. [2] His solution - a glass beam made from a series of glass blades connected at their ends and at their mid-points to form a rigid cantilever - relies on a bolted connection, the loads evenly distributed by a metal bezel fitted in the bolt-hole.