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Quai Branly Museum's challenging structural concept realised with ArcelorMittal steel
Located along the Seine in Paris, the Quai Branly Museum consists of three buildings, each with a distinct identity: the actual museum, the administration building with a façade full of plants, and the property devoted to the collection management and library, with its Aboriginal paintings. The design called for a solution made of steel, ArcelorMittal supplied hot rolled sections, composite flooring deck and aesthetic façade panels.
The quite exceptional site with a curved shape on the edge of the Quai Branly and the river, 100 metres from the Eiffel Tower, had been selected to accommodate the International Conference Centre (Francis Soler, prize-winner of the 1990 competition), one of the major projects abandoned by François Mitterrand.
Nouvel's museum project is conserving the site and only occupies one third of it, transforming itself into a bridge to allow easier access to the rather sumptuous garden designed by Gilles Clément (18,000 m2). Omnipresent all along the rue de l´Université, it offers unexpected views and is also directed northwards along the quayside, protected from the noise by a large plate glass wall (200m long and 12 m high). With undulating paths, it is planted quite densely with 178 trees and more than 72.000 different plant species.
This Seine-side development ends to the west with the amazing planted façade, the vertical garden of the administration building, designed by Patrick Blanc. The volume itself is designed to create a transition to the adjacent traditional Parisian buildings.
From the Eiffel Tower the morphology of the museum displays its structural and architectural aspects. An articulation of two entities is discernible, almost a fracture of the building which immediately calls into question its actual structure. The complexity of the concept, at the time of the competition, encouraged the use of a steel structure, a fine gesture when brushing against the iron lady, the Eiffel Tower.
Those who restrict the work of Jean Nouvel solely to the pleasure of metaphoric and contextual architecture must study the framework of the museum, the cantilevers of Lucerne, those of Lille and Madrid. So many designs which, whilst appearing to cock a snook at the architectural technique, nevertheless push it to its extremes with panache. The ramp providing access to the collections, the two levels constructed on 23 pairs of pendular posts, the overhanging museum showcases placed along the floor cantilevers, the front and rear facades, the latter planted, constitute the challenges.
The Museum Building & its Structure
Installed on the concrete infrastructures that house the auditorium, the reserved areas, the workshops and car parks, the steel structure of the museum is built in the form of a bridge which has two superimposed decks (level + 42 and +53) supported on pendular columns arranged at random like the trees of a sacred forest, one of the themes underlined by the text of intentions at the time of the competition ("It is a place marked by the symbols of the forest, the river and the obsessions of death and oblivion..."). This concept involves spans of up to 34 metres and consequently cantilevers extending to 15 metres.
200 metres long, these two decks are separated into two blocks (east and west) by an expansion joint level with the fracture. The random arrangement of the posts influenced the choice of structural style. The result of a complex iterative process, the final topology of the structure is derived from a discussion held between Jean Novel and the Jacques Faure and Florent Millot engineering teams. In an attempt to rationalise the structure over time, the latter surrendered to the demands of the architect and finally opted for an irregular frame or reticulated beams and joists connected an interacting14 cm thick floor, the whole installed on articulated tubular posts with a 700 mm diameter.
The position of the posts and the links of the beams to their cantilevers made it difficult to embed the posts, a problem that was resolved by their head and foot articulations. Although this solution resolved the problem, it imposed a different concept for the general stability of the work. This stability is provided by 3 technical concrete cores in the west section, the single core in the east section required the addition of a huge stabilising portico at the point of the fracture. For each of these two levels the framework of beams is connected by linking joints to the concrete cores so that the horizontal forces of the steel structure can be transmitted to them.
The construction of such a mechanical system was nothing if not a delicate operation. Unlike the traditional structures, whose node coordinates are inscribed on an orthonormal grid, the random location of the posts do not provide an easy reference for assembly. They were arranged by the surveyors on a triangulation principle. They were temporarily blocked perpendicularly whilst awaiting assembly of the beam grills. Despite this concern for precision, the metal constructor Joseph Paris had to anticipate the following, explains Rodolphe Cétin, the owner of the site: "The development of a system of corollas welded to the posts in the workshop enabled the beams to be regulated precisely for their welding on the site".
The first level of the deck accommodates the ramp which opens out into a distribution volume leading to the floor of permanent collections. It also supports the museum showcases in cantilevers located on the Seine side. Fifteen metres above it, the second deck supports underneath a level of suspended mezzanines interspersed with framework posts, but does not touch it.
On the open side this deck houses what is already a new Parisian icon. With its panoramic floor terrace moulded in deactivated matrix concrete, broken into multiple latex joints, edged in pools, punctuated at both ends by the library and restaurant covered with a glass lens, the latter level offers novel views of the capital, a sumptuous gift. Here the Eiffel Tower, a couple of steps the Seine, opposite the Palais de Chaillot, a little further the Grand Palais, the Dome of Les Invalides, over there, Notre Dame, the Sacré Coeur.
Based on an initiatory path which starts in the garden, the museum library brings the visitor to the heart of the museum by a 180 m long ramp, constructed of welded steel plates linked with a white plaster which gently winds to take account of the rest landings conforming to the regulations of accessibility. At every turn installed on and suspended from the structure of the first deck, then cutting through it, this ramp, together with the random positioning of the posts, was one of the major structural constraints of the project. After several circumventions, particularly around the extraordinary silo in the reserved areas, then after a loop on the temporary collection floor, it returns to the general structure of the building, gaining height and opening into the museum library space at the first level. For obvious reasons of convenience to the users, the natural frequency of the ramp was adjusted to 5 Hz.
Intended to house the musical instruments, the reserve silo is lined at a height of 24 metres with 220 curved glass partitions. Completely separated from the rest of the building which it crosses throughout its height, the silo consists of a circular concrete core which supportsseven metal platforms with a total area of 900 m2. Composed of galvanised steel joists and bent sections, these platforms, supported by tubular posts, are covered with a steel composite flooring system , designed to take a load of 5 kN/m2.
Suspended Mezzanines, Technical grid and Overhanging Boxes
The space between the two shutter levels is extended at every turn to double its height or punctuated by mezzanines suspended on tie bars. These almost aerial floor surfaces form an impressive insert, a metaphore for travelling, the far off, which does not make you forget the engineering involved.
A technical platform has been arranged underneath the shutter level in which run the networks and ventilation ducts. With a thickness of approximately two metres, it consists of a grated grill suspended on the structure. Circulation routes are arranged across the frame for the maintenance teams in this insert, which is painted black. Drilled with regular holes, the grill provides for the passage and arbitrary adjustment of the lighting strips of the museum library.
Suspended multi-coloured “boxes” seem to be inlaid into the façades and offer more intimate exhibition spaces inside the museum. Assembled on site, in a metal structure, the26 boxes of different sizes, on a single or double level, are provided with an composite floor and an insulating sandwich panel enclosure (steel surfaces, polyurethane core). Stratigraphed resin cladding, in ten different shades, is fixed to these panels by means of galvanised steel handrails. Being light, therefore, compared with the two decks and the columns, the dynamic behaviour of these boxes has been carefully designed to ensure that the work maintains a natural frequency of 3 Hz recommended by the European regulations. The purpose of this basic limit is to guarantee comfort of the users and to avoid an unpleasant vibrating sensation from the structure that is clearly felt on certain footbridges.
Innovating Light Control
The control of light in the museum is obviously crucial insofar as the architects, in addition to complying with the strict lighting regulations (approx. 50 lux), also wanted to create a specific lighting ambiance tinted with mystery, obtainable with the north and south orientations of the museum facades. The first (north side), interspersed with the coloured showcases, is unusual.
In the north facade, which is interspersed with the suspended boxes, it consists of a filtering network of sheathed chestnut metal tubes forming a trellis lined with 1500 glass faces. In the shape of a lozenge, each square includes in its facing a dual function film. It lowers the light transmission so that it gives the museum the atmosphere of a dense forest. It is one of the pieces of an image of rural settings associated with the origins of the objects exhibited for which all the glass partitions are designed.
Composed of photographs from the database of Patrick Blanc, it starts in the east with an African forest, continues through a savannah region, and finishes in the west with the forests of Asia and Oceania.
The image is superimposed on the profile of the trees in the garden, the whole mixing reality with fiction. The opening of the extremely small windows in the multicoloured showcases depends on the works exhibited in them. A symbol of this museum, which is actually built around one collection, integrated in the museum library and vice versa. Although they are different in their texture and in the size of the openings, these showcases are reminiscent of those designed by Carlo Scarpa at the entrance to the Castel Vecchio (Old Castle) in Verona.
Orientated southwards, the rear façade is distinguished by the floor of temporary exhibits and the much larger floor of permanent collections.
Located at the west end under the first shutter, and appearing at the rear as a protuberance of the building, the floor of temporary exhibits is presented as a twisted semicircular volume enclosed by three rows of panels, initially of screen printed bulging glass partitions, then of white metal panels, forming a canopy progressively elevated in a sweeping movement. In this flight, the glass panes are perpendicular to these white shells and reflect a light that is not dazzling in the interior.
The entire glazed façade of the permanent collection is protected by a point screen printed film veneered on the outside. This technique makes the screen printing invisible from the inside and offers the visitor an unbroken view of the glass partition. The outer canopies of folded metal are controlled electrically. In the form of Italian style shutters, these elements are controlled by vertical cams to which they are connected in clusters of five. Lined in a gradation of eight colours, ranging from brown to red, a limited number of canopies on the west side are painted white as if to simulate a random sprawl of the façade. The red colour is also used for the underside of the building. With its wall of polygonal panels, the garden path underneath the museum gives the impression of passing under a strange animal whose stomach constitutes a sixth façade.
Jean Nouvel, Françoise Raynaud, Isabelle Guillauic, Didier Brault
Gardens: Gilles Clément
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