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28 STRUCTURE AS ARCHITECTURE▲ 3.11 Hall 26, Trade Fair, Hanover, Germany, Herzog + Partner,1996. Three catenaries span between masts.▲ 3.12 Exposed steel catenary members connect to aninterior mast.bases. If ribs are inclined from the vertical or curved in elevation theymay be propped by other ribs to achieve equilibrium, as in the case of aribbed dome. Ribbed structures generally enclose single volumes ratherthan multi-storey construction. By restricting the height of these structureseffectively to a single storey, albeit very high, designers avoidpotentially compromising a pure architectural language of ribs withadditional interior load-bearing structure.Ribs visually dominate each of the four structurally independent Licornefootball stadium perimeter walls at Amiens (Fig. 3.13). Elegantly curvedand tapered, the ribs shelter the spectators and accentuate a sense ofenclosure. The combination of widely spaced ribs and glazing providesan unusually high degree of transparency and openness – daylight is maximized,spectators are more acutely aware than usual that the game isbeing played outside, and they can enjoy the surrounding townscape.A prop near to the base of each rib provides its base-fixity and stabilityin the transverse direction. Unusually configured moment-resistingframes within the ribbed surface resist longitudinal loads. In these framesthe ribs function as columns, and the horizontal tubes or girts, rigidlyconnected at 1 m spacing up the ribs, as beams (Fig. 3.14). The integrationof girts with ribs to form these multi-bay frames avoids the needfor a more common and economical form of resistance, such as diagonalbracing whose geometry would clash with an otherwise regularorthogonal pattern of ribs and girts.A similar combination of primary structural ribs and secondary horizontaltubes defines the architectural form of the Reichstag Cupola, Berlin(Fig. 3.15). In this case, ribs lean against each other via a crowning compressionring. An internal double-helical ramp structure supported off