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158 STRUCTURE AS ARCHITECTURE▲ 7.55Internal horizontal trusses in the library.contribute a diaphanous softness to the façade. Other internal boxtrusses support the skin in double-height spaces such as the library. Butthese are detailed completely differently. Diagonal web members,together with four parallel tubular chords, achieve new qualities of intricacyand ornateness (Fig. 7.55). Their transparency and visual complexitycompliment similar qualities present in the glazed and mechanicallyshuttered curtain-walls. It is worth reflecting on how greatly the aestheticqualities of the space would change if the existing trusses werereplaced by solid box or tubular-beams.Another example of structural detailing for lightness can be observed inCharles de Gaulle Airport, Terminal 2F, Paris. Whereas in the first visitto the building it was noted how the massive exterior structure signalledentry (see Fig. 4.30), now the structural lightness inside the terminal isexperienced. A 200 m long ‘peninsula’ that houses departure loungesand aircraft walkways juts out from the air-side of the main terminalbuilding. A series of transverse portal frames whose detailing is so ‘light’that the whole structure almost reads as a space frame, supports itsroof (Figs 7.56 and 7.57). Structural detailing is not locked into anorthogonal grid but responds to the roof form that appears like anupturned boat hull. The truss nodes map the gently curving roof contours,and via innovative light-weight tension-spokes, the trusses wraparound and under the floor slab. The structure delivers a light-filledspace while displaying a remarkable degree of lightness. Compared tothe heaviness of the terminal land-side concrete wall and ceiling surfaces,this air-side structure looks as if it could take off!