Space invader: essentially an exercise in enclosing vast tracts of space, this new trade fair hall in Frankfurt is distinguished by its great roof which is both sculptural and efficient.

Flying into Frankfurt, you spot it immediately. A muscular, undulating roof like a gargantuan ribcage marks the latest addition to Frankfurt's Messe, the vast agglomeration of trade fair halls to the west of city centre. The fair's proximity to both city and airport is one of the reasons for its commercial success and ongoing physical expansion. Like some kind of superscale city-within-a-city, it continues to evolve as new and ever bigger halls are added to the existing complex. Here, size really does matter. The entire site is dominated by Europe's tallest building, Murphy Jahn's Messeturm, a chunky, Crayolashaped skyscraper. Despite its prosaic appellation, Nicholas Grimshaw's Messehalle H3 is a gleaming, streamlined world away from the dull sheds and hangars that make up most of the Messe. In terms of scale, it is the biggest building on the site, with a whopping 40 000 sq ft of exhibition space spread over two cavernous levels. In civic terms, it occupies a prominent locale, completing the southern perime ter of a large urban square. By designing the structure to span 165m lengthways, the front wall is relieved of load-bearing functions, so it could be entirely glazed, forming a huge vitrine that dramatically addresses and connects with the square. From his earliest years, Grimshaw has been determinedly fascinated by the potential of technology, but as the practice's work has matured, it has embraced the challenge of designing very large buildings such as Waterloo International (AR September 1993) and the Eden Project (AR August 2001). These are more than simply big, dumb sheds; instead they are rather clever roofs. In particular, the wide-span roof has come into its own as an architectural, structural and sculptural element. Enclosing the maximum area with the maximum structural efficiency, H3 represents the latest manifestation of a continuous line of architectural thinking.

A fundamental requirement was that the upper hall should be entirely column-free to maximize internal flexibility. (The architects claim that it is the largest column-free space in Europe.) Devised in collaboration with Ove Arup & Partners, the roof is essentially a conventional folded plate vault curved and twisted to make it both more structurally efficient and tectonically expressive. Steel members form a single continuous folding grid, in which compressive and tensile zones can be clearly distinguished. Each of the five roof arches is flexed across its width, turning it into a stiff double curvature shell. Intermediate valleys between the arches are also distorted to achieve the same effect. Such an unorthodox form was made possible by the use of sophisticated customized computer software to analyze and plot the flow of forces in three dimensions.

Moulding the roof into double curves has several advantages: it not only stiffens the entire structure, but the resulting shallow arched form is also both more elegant and more efficient, reducing the internal volume requiring air-conditioning. In structural terms, the roof operates like a spider's web, at once light yet immensely strong, pared down to the absolute minimum required to provide the necessary support.

The roof deck is formed from prefabricated stressed skin panels comprising two profiled steel decks riveted together with their troughs aligned in opposite directions. Conforming to the structural geometry, these are manufactured with an in-built twist. Yet because of the repetitive nature of the roof, only 60 different panel types were required, so reducing manufacturing costs. Roof vaults are supported at their ends by big A-frames with large raking struts exposed. A conventional concrete post and beam structure holds up the upper floor.

The sensuous, swelling form of the roof is best appreciated from the side or from underneath, within the soaring volume of the exhibition hail. For visitors, this experience is like being inside the belly of some prehistoric beast. Clerestory glazing draws daylight deep into the interior and accentuates the undulating form of the roofline. Curved booms suspended within the arches contain lighting and air handling plant.

On either side of the exhibition halls are four levels of foyers and break out areas which have their own animation and drama as people scuttle around the luminous concourses and promenade up and down the escalators. Taming and civilizing such an unwieldy spatial behemoth is never easy, but Grimshaw manages to crack the whip with a good deal of rigour and style.

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Nicholas Grlmshaw & Partners. London

Project team

Nicholas Grimshaw, Neven Sidor, Ingrid Bille, Moritz May, Stephen Ridell. Robin Kirschke, Simon Beames, Ben Heath. Wolfgang Stockinger, Adam Firth, Carl Shenton, Jens Hardvendel, Ruby Kenzi, Ted Finn, Birgit Greulich, Max Fawcett, Giles Omezl, Jorg Winkler, Tlmm Schoenberg, Shoalb Rawat

Structural engineers

Arup GmbH/Schlaich Bergermann/BGS/Hahn & Bartenbach

Services engineers

Kuehn Bauer & Partners/HL Technik/Dorflinger

Photographs

Waltraud Krase