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142 STRUCTURE AS ARCHITECTURE▲ 7.19 Guggenheim Museum, Bilbao, Spain, Frank O. Gehry & Associates, 1997. View ofthe museum from the Puente de La Salve bridge.(Fig. 7.19). Although the structure of this remarkable building liesmainly hidden within its billowing and twisted sculptural forms, in severallocations its skeletal steel structure is exposed. The most accessibleand informative area of this exposure occurs at the tower (Fig.7.20). In conjunction with the long gallery, the tower ‘holds’ the Puentede La Salve bridge to the main body of the museum. The exposed towerstructure, visible from the bridge, explains how other building exteriorsurfaces are structured. Rather unexpectedly, a conceptually simple triangulatedsteel framework supports the geometrically complex skins.Compared to the audacious titanium clad three-dimensional curvedsurfaces, the adjacent structural details of nuts and bolts and standardsteel sections appear quite crude. Their ordinariness disguises theextent of the underlying structural analytical and design sophistication.▲ 7.20The tower structure.On a far smaller scale, and more overtly than at Bilbao, Frank Gehryexpresses the nuts and bolts of structure inside the Fisher Center,Annadale-on-Hudson, New York. Curved steel ribs and bent horizontalgirts are the means of achieving the dramatic sculptural walls that forma protective skin around the main theatre (Figs 7.21 and 7.22). SteelI-sections, their flanges welded to curved web plates, rise from theirfoundations and span a four storey volume to gain support fromthe concrete walls that enclose the theatre. Braced within their planes,the entire construction of these ribbed walls – the inside surfaces of thestainless steel cladding sheets, the girts, ties, braces, cleats and even the