Arched and curved structures

Arches are convex structures that are designed primarily to resist compression, as a result of their shape and the form of loading acting on them. Arches are theoretically of parabolic form when subject to uniform loading, but they can be circular, or even made from multiple linear elements. Arches also resist bending moments which are also induced due to non-uniform loading, or the deviation of the arch from the idealised shape in which the lines of thrust (compression) are located within the member cross-section.

Arches in steel may be made of I-sections that are either curved to shape (see Colour Plate 22), or made as a facetted arch from multiple straight lengths. They can also be in the form of fabricated members, such as trusses. Arches may have rigid or pinned bases, or a combination of both. Figure 2.5 shows an excellent example of external and internal arches within a multi-storey building used to great structural advantage by spanning over the railway lines at the Broadgate development, London.

Tubular members are excellent for use in arch construction because of their resistance to buckling and, hence, the few lateral

restraints that are required. At the Windsor Leisure Centre, an arch with variable curvature was continued outside the building envelope, as shown in Figure 2.6. See curved tubular trusses in Colour Plate 4 and the glazing supports in Colour Plate 14.

The roof of the great glasshouse of the National Botanical Garden of Wales used the concept of a curved roof consisting of arches of similar curvature but of reducing span to create a toroidal shape (like a slice through a car tyre), as illustrated in Colour Plate 2. The maximum span of 60 m is achieved with only 324 mm diameter circular hollow sections (CHSs) which support the glass roof.

Hong Kong's new airport uses a variety of novel construction forms, including a long curved canopy over the walkway, as illustrated in Figure 2.7.

Steel members may also be curved in the horizontal plane rather than in the vertical plane, as illustrated in Figure 2.8. In this case, the

Architecture SteelRichard Rogers Canopy

2.6 Arched roof at Windsor Leisure Centre (architect: FaulknerBrowns)

2.8 Curved canopy at the Strasbourg Parliament (architect: Richard Rogers Partnership)

2.6 Arched roof at Windsor Leisure Centre (architect: FaulknerBrowns)

2.8 Curved canopy at the Strasbourg Parliament (architect: Richard Rogers Partnership)

members are subject to bending and torsion, which is a complex interaction. Inclined curved members can also be used to great effect but, in this case, additional horizontal or torsional support is required to counterbalance the forces. The Merchant's bridge in Manchester utilises this principle, as illustrated in Colour Plate 18.

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