Glass gangway.

A glass bridge is a disturbing thought, for by and large people like to see there is something solid underfoot when crossing a void. Experiments with infant perception of space have shown how babies, left to crawl on an elevated surface of partly opaque and partly clear glass, peered into but instinctively avoided getting onto the glass. But the invention of structural glass systems made the thing inevitable. In Rotterdam, Dirk Jan Postel's glass bridge spanning a street 3.2 metres wide connects buildings (converted water filtration plants) on either side at second floor level, and so links the otherwise separated offices of Kraaijvanger-Urbis Architects. From the inside, says the architect, the bridge is experienced literally as a leap into the unknown.

The bridge was to be used constantly, and the decision to use glass for its structure, without any auxiliary construction, was taken in the spirit of experimentation. Floor plates of 15 mm laminated float glass rest on two laminated float glass joists following the line of momentum. Side walls, composed of 10 mm tempered and 6 mm toughened glass sheets, support themselves and the similarly composed roof. The glass plates are joined together and to the buildings by stainless steel fixings whose design and location express functional essentials of the structure. For example, the points at which the wind load is diverted are distinguished from the four suspension points, and crescents indicate the transfer of forces between roof and side wall.

Apart from the anticipated sensation of stepping into a void, there have been other unexpected feelings produced by engaging with a transparent pathway: the delight in the early morning of seeing the prisms of light cast around by sunlight through glass, or the disorienting Never Never Land experience of having your shadow snipped off and silhouetted on the pavement metres below. But for the full awe-inspiring and breathtaking effect, the bridge should really traverse a more dramatic chasm, such as the great grey green greasy Limpopo River and its jungly denizens.