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RELATIONSHIPS BETWEEN ARCHITECTURAL AND STRUCTURAL FORM 41▲ 3.39 Visually complex roof structure over the pool. ▲ 3.40 Exchange House, London, England, Skidmore, Owings &Merrill, 1993. Arches enable the building to span the site.profile increases the truss complexity and reduces structural efficiency.Relatively large truss member sizes are required even though they aredesigned for heavy snow loads (Fig. 3.39). Although a lack of structuralhierarchy among the many structural members obscures the primarystructural form, a combination of timber’s warm natural colour, unobtrusivetimber connections and the filtering of natural light by the structure,contribute towards memorable architecture.CONTRASTING FORMSArchitectural and structural forms contrast where a juxtaposition ofarchitectural qualities such as geometry, materiality, scale and textureare observed. In the examples that follow, geometric dissimilaritybetween forms is the most common quality contrasted. At ExchangeHouse, London, parabolic arches support a building rectilinear in planand elevation (Fig. 3.40). The contrast between forms arises primarilyfrom the need for the building to bridge underground railway lines, buteven the exposed transverse cross-braced bays at each end of the buildingare unrelated to the architectural form (Fig. 3.41).An element of surprise is also a feature common to buildings with contrastingforms. As one approaches a building and becomes aware of itsarchitectural form one usually expects to discover a certain structuralform based on one’s previous architectural experience. If the actualform is considerably different from what is anticipated then it is likelythat architectural and structural forms contrast.▲ 3.41 A transverse exterior crossbracedframe.Well-designed contrasting forms provide many opportunities for innovativeand interesting architecture. Most examples of contrasting formscan be attributed to designers attempting to enliven their work, but