Structural Design for Architecture
Fig. 1.12 Building for IBM Europe travelling exhibition.
Renzo Piano, architect/engineer, Ove Arup and Partners,
structural engineers. A complex, highly efficient vaulted
structure like this would not normally be used for a short-
span enclosure. It was justified in this case due to a
requirement for a lightweight structure for a portable
building. The choice of lightweight materials - timber and
plastic-was also sensible. [Photo: Ove Arup & Partners]result of the application of load.^3 In modern
practice, vaults or domes are normally used to
achieve high levels of structural efficiency,
either because a very long span is required or
because a special requirement must be satis-
fied such as the need for a very lightweight
structure (Fig. 1.12).1.3.3 Tents and cable networks
Tents and cable networks are tensile equiva-
lents of domes and vaults (Fig. 1.13). The in-
ternal forces which occur in these structures
are those of axial tension and they are there-fore, like their axial compressive equivalents,
potentially highly efficient in resisting load.^4 As
with domes and vaults they are used in situa-
tions in which high structural efficiency is
desirable, such as for long spans or where a
lightweight structure is required.1.3.4 Combined-action structures
A fourth category of structure is one in which
the load is resisted by a combination of
bending and axial internal forces. The ubiqui-
tous portal frame (Fig. 1.14) is perhaps the
best-known example of this but any structure
which is neither purely 'form-active' nor purely
'non-form-active' will carry load through the
combined effect of axial and bending action.
These structures have properties which are
intermediate between those of the post-and-
beam arrangement, which is inefficient but
simple to construct, and the arch, vault or
cable network, which are highly efficient but(^10) 3 See Macdonald, Structure and Architecture, Chapter 4. 4 See Appendix 1.