Report: CNIT in Paris
With around a dozen new high-rises under or shortly to start construction, the Paris business district of La Défense is currently experiencing its third spring. The development of the district started with a building which is arched over by the largest reinforced concrete shell structure built to date. The roof of the Centre des nouvelles industries et technologies (CNIT), which was built in 1958 as an exhibition hall for the French association of machine tool manufacturers, measures 218 m in span and 46 m in height. The triangular shape of the former factory grounds considerably influenced the design of the architects Robert Camelot, Jean de Mailly and Bernard Zehrfuss. De Mailly came up with the decisive concept sketch: a gigantic arched structure resting on three abutments: how that would be realised was still to be resolved. Pier Luigi Nervi and Eugène Freyssinet, two of the foremost pioneers of reinforced concrete construction, were consulted but their concepts did not convince the client. The design by Nicolas Esquillan, who headed the engineering team at one of the three contractors engaged on the project, offered more certainty of completion on time and budget. He envisaged a twin-shell roof structure composed of six similarly shaped segments. Ten reinforced concrete ribs run radially from the abutments to the crown inside each segment. The shells are only 65 mm thick at their thinnest points, while the prefabricated ribs have a width of 60 mm and a depth of 1.9 to 2.7 m. A total of 44 steel cables connect the three abutments below ground to contain the horizontal component of the outward arch thrust.
