Cable Stayed Roofs
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UDC 624.911.2 ORDINARY MEETING A paper to be presented and discussed at a meeting of the Institution of Structural Engineers, 11 Upper Belgrave Street, London SWIX 8BH, on Thursday 25 October 1984, at 6.OOpm. The design and construction of cable-stayed roofs J. A. Thornton, BSc, CEng, MIStructE Ove Amp (Er Partners John Thornton graduated from Nottingham to work in their London office. He left for a period University in 1968 and joined Ove Amp & Partners to becomeanAssociatewiththeWhicheloeMac- farlane Partnership and, after rejoining, was responsiblefor the Fleetguard building, He became ject structural engineer for the Lloyd’s redevelop- an Associate of OAP in 1982 and at present is pro- ment. Synopsis The paper discussesthedesign of cable-stayed roofs, withparticular reference to a number of buildings recently constructed. Introduction In the last few years, designers in this country have been responsible for a number of buildings with cable-stayed roofs. Typically, in the past, cable- stayed structures have been associated with very long spans where they offer strong technical advantages, although this is obviously a generalisation to which there will be exceptions. Perhaps what is most interesting about these recent buildings is that, in general, the spanshave not been very great and a variety of solutions were possible. The reasons for using a cable-stayed roof in these circumstances are complex, but in all cases the structural support system becomes the visual force which influences all aspects of the design. It would be beyond the scope of this paper to discuss the whole subject of cable-stayed roofs other than superficially, and so the emphasis here is on those recent buildings that represent something of a change in direction. Before discussing specifics, it is worth looking first at some historical aspects. Fig 1. The Albert Bridge Pure tension members have been used in many structures such as ships, cranes, radiomasts, roof trusses, grandstands, aircraft, and bridges (Figs 1,2),in some casesgoingback as far as recorded history. Interesting examples in recent British building include the grandstand at Crystal Palace and those of Jan Bobrowski, the Skylon, the aviary at London Zoo, and the Botanical Gardens at Edinburgh. The designs have changed with materials and technologies. In the 19th century social, technical, and economic developments led to ademand for a series of new types of structure whichneeded large column-free spaces, such as exhibition halls, market halls, and railway stations. Using the materials of cast iron and wrought iron, Victorian designers created buildings that satisfied this demand and were some of the most exciting and interesting structures of the time. Many of these structures made use of tension rods and were articulated in a way that was to be echoed later, but Sir Henry Bessemer’s process for making steel in large quantities marked the end for this type of structure. The economics of using rolled-steel sections with bolted, riveted and, later, welded connections, together with improved engineering understanding, meant that the rigid steel frame and the welded truss became the norm for such buildings. Some aspects of the Modern Movement in architecture also favoured the rigid frame and, of course, for a long period there was great interest in exploiting the potential of reinforced concrete. However, a number of architects and engineers became interested in structures that expressed how they worked in a more direct way. Cable- stayed roofs have a diagrammatic quality and generate an aesthetic of detailing that satisfies this interest in legible, articulated structures. In this respect the Centre Pompidou (Fig 3) can beseen as a key building in its detailing and the extensive use made of pure tension in primary and secondary structure; the basis of many of the ideas developed subsequently are found here. A few years later the Cummins building at Shotts, while not cable-stayed in the accepted sense, made use of rods from primary trusses to assist the span of secondary castellas. The first of this group of cable-stayed roofs to be designed was ___-_ ___ . - The Structural EngineerNolume 62Amo. 9ISeptember 984 275
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Structural design
