CENTRE GEORGES POMPIDOU, PARIS, FRANCE

The building contains an exhibition of Modern Art, a library, offices and terraces contained in the steel superstructure. Below it is a concrete substructure occupying an area on plan of 160 x 100 m.

The superstructure has fourteen plane frames, six storeys high, with a typical floor height of 7 m. Each frame consists of two 850mm diameter round tubular columns, 48 m apart, each column supporting six cast steel brackets which have a pinned connection with the column; each bracket takes a downward load, at its inner end, from the deep lattice truss supporting the floor, and this is balanced by the tension force in the tie attached at its outer end. The main lattice truss spanning 44.8 m in the east-west direction has a mid-span depth of 2.82 m between the top of the twin 419 mm diameter tubular top chords and the bottom of the twin 225 mm diameter solid rod bottom chords. Single alternating tubular and solid diagonal members, taking compression and tension respectively, are attached to the top and bottom chords by welding to the cast steel connections that are at nodes on the chords. The cast steel nodes on the top chord also receive ordinary rolled steel I-beams, generally 500 mm deep, spanning in the north-south direction between the trusses. The I-beams and a 110 mm deep concrete floor slab above it act compositely. Under vertical loading each internal frame functions independently of the others and joints are provided in the slab and in the steel beams to allow each truss to deflect independently. Resistance against horizontal forces is provided, on the east and west facades, by 62 mm diameter high strength, pretensioned diagonal bars; the cross-bracing is in panels two storeys high and connected to the columns and floor deck by horizontal tubular bracing in alternate bays at every other floor level. Horizontal forces transferred to the gable ends are resisted by the main lattice trusses which are connected together by diagonal tubes. The diagonal tubes could not be taken to street level between the columns, for planning reasons, and therefore heavy cross-bracing has had to be provided outside the columns at this level. In general, solid round bars take tension and tubular sections take compression.

Other important elements in the composition of the facades are the secondary beams and columns. The secondary beams consist of two steel channels usually strengthened by steel flats in tension and tubes in compression that make it into a truss; the secondary columns consist of four steel angles symmetrically placed and connected to each other through spacers. The secondary beams span to the cast steel brackets and may easily be changed in position.

The truss and bracket arrangement at each level is based on a Gerber system. With a distance of 48 m between column centre lines and a live load of 5 kilonewtons per sq m, these floor trusses had to be heavy and comparable in size to those of a bridge. Double members were used for the top and bottom chords of the truss to minimize the truss depth and to provide it with some stability when in position. In spite of its size, large vertical movements of the truss, and therefore differential movements between trusses, had to be accepted. A result of this is that, in alternate bays of the building, floor beams have to have pinned connections with the truss at each end to allow this movement to occur; in the remaining bays the floor beams have fixed connections with trusses in order to stabilise the trusses against torsion. At this scale another movement which obtains great importance is the shortening of the top boom of any of the trusses under load; this causes considerable bending in the columns, which they must be designed to resist. Considering all these movements, the concrete floor slab is split into separate panels by 5 mm joints running in the east-west and north-south directions, thus preventing stresses in the slab.

Concrete panels over the truss are precast but the rest of the floor slab is cast in place. In spite of the movement joints, the slab is still able to act as a continuous horizontal diaphragm spanning between the gable walls, because the cast-in-place panels are attached to each other by steel connectors at intervals.

Notes:

cast steel литая сталь

gable wall фронтонная стена

Gerber system система Гербера

kilonewton килонъютон

plane frame плоская рама

pretensioned adj. предварительно напряжённый

Ответьте на вопросы к тексту

1. What kind of building is it?

2. What are the main elements of its superstructure?

3. What is the structure of the plane frames?

4. How is resistance against horizontal forces provided?

5. What are the features of the secondary beams and columns?

6. Why did the floor trusses have to be heavy?

7. How were differential movements between trusses accepted?

8. Why is the concrete floor slab split into separate panels by joints?

9. How much was precasting used?

10. Why is the slab able to act as a continuous horizontal diaphragm?