Specialist know-how: Advances in structural glass design
Since the 1980s architects and engineers have become increasingly interested in creating structures that consist completely of glass. Glass combines the characteristic of transparency with the capacity to create a climatic barrier between exteriors and interiors. Glass is also a sustainable material. Created from sand, it is 100 % recyclable and requires no corrosion proofing. The glass structure of the greenhouse facades in the Cité des Sciences et de l'Industrie at Parc de la Villette in Paris (ill. A) designed by the engineer Peter Rice (RFR, London) and built in 1986 exemplifies that an intelligent combination of materials can lead to safe and reliable glass structures 1. Every glass structure needs to guarantee sufficient structural safety. This basic requirement can be met particularly by laminating or adhesively connecting multiple layers of glass. The glass industry typically manufactures maximum panel sizes of 6 ≈ 3,2 m, due to reasons of economy and production technology. This is why connectors often become necessary that can also bear tolerances related to construction and production. Typically, they are made of steel. We at TU Delft are convinced that a combination of glass and adhesives can be just as successful as steel and welding technology. In the follow of constructing the greenhouses at La Villette, engineers across the world met the challenge of translating all building elements into structures completely made of glass - in other words, transforming beams, columns, ceilings, roofs, facades and walls into safe all-glass structures. A glass bridge that was erected in Rotterdam in 1994 demonstrates this development very well. Practically all building components of the bridge, designed by Dirk Jan Postel of Kraayvanger Architekten (ill. D), feature all-glass elements 2. The glass deck is at a height of 3 m. We used laminated glass for all parts and applied a safety factor of 10 for the structural calculations. The permissible tensile load was set at 20 MPa. At that time there was no set of rules or norms for glass structures. The 20 MPa were a result of reverse calculation from tables that determined the required glass thickness for windows in relation to building height. The architect demonstrated the performance of the concept to the skeptical users by applying a test load comprised of densely packed volunteers. After the Rotterdam glass bridge, a series of similar bridges followed. An accident led to the destruction of the glass bridge erected above the entrance of the zoo in Arnhem. In 2012 the operator of a loaded forklift hit the bridge. Although both beams were completely destroyed, the safety concept worked. The bridge didn't collapse and was still useable, even though the margin of safety was significantly reduced (ill. B).
