Jörg Schlaich on Lightweight Structures

Nigel O'Neill

Membrane structures, cable nets, folding bridges, glass net walls, glass grid roofs, solar chimneys - one does not miss an opportunity to hear first hand a key innovator of these types of amazing structures. Opening with a brief and touching reminiscence of Peter Rice, Jörg Schlaich outlined the theme for his lecture: lightweight structures, starting with a review of Schlaich's bridge designs, then of his roof designs and finally of his power generation projects.

Personally I found the section of the lecture relating to glass grid walls and roofs to be the most fascinating. An important thing to remember about glass is that because of the way that it is manufactured glass becomes very expensive if it is warped (one corner out of the horizontal or curved plane). Schlaich presented his method, based on mathematics, of producing interesting curved geometries without warping: basically if one starts with a continuous line and moves it along another smooth continuous line that is at right angles to the "sweeping" line then a curved grid is generated with each rectangle of four grid points lying in the same plane. It is inspiring to see such an elegant use of analytical geometry to solve a practical problem - the curved organic shapes could be generated but not at the expense of impractical warped panels. At some stage Schlaich made the point that Nature was sometimes not that useful for providing inspiration for solving engineering problems and that instead we needed to look to mathematics for inspiration.

Returning to the notion of duality, the inverse of grids is nets and Schlaich presented examples of glass nets used as large walls: the structure is provided by tensioned cables with glass panels supported at the nodes where the cables cross each other. The glass net at the Foreign Office, Berlin spans several storeys and brings new meaning to the term "transparent structure".

Membranes comprised of textiles are the lightest structural material to date and can be supported by no more structure than a positive difference in atmospheric pressure. Using his own person as a demonstration aid, Schlaich showed how structural textiles could be manufactured, cut and stitched into easily handled components (e.g., like a jacket) and installed and adapted to any three dimensional curved geometry (e.g., like his own body - the three dimensional curved geometry being a modest paunch). Taking this logic and applying it to something bigger, like a sports stadium, and one gets results like the AOL Arena in Hamburg, which is a textile membrane roof supported by back anchored cables.

Jörg Schlaich is one of the greats. I am greatly impressed by his work and also his wit and charm. Schlaich is a believer in the idea that engineers should be generalists and certainly the breadth of his own work, research and concerns, clearly demonstrate what can be achieved if one is open to new ideas and open to approaching problems from different angles.

Nigel O'Neill is an Associate in Roughan & O'Donovan Consulting Engineers and specialises in bridge design.