Creating a building’s multi-purpose exo-skeleton from bronze aluminium blades
An artistic way to optimise energy
The Conex is a new office block that recently opened in March 2018, located in rue de Tournai, a busy side street that runs alongside Lille Flanders railway station. Its flowing, shimmering facade is a real eye-catcher: it is made up of over thousand sun light diffusing reflectors that change colour according to the sunlight and viewing angle.
Paris based architects Chartier-Corbasson designed this building in partnership with VS-A an engineering practice specialised in designing building envelopes to optimize building energy ratings. Their approach was driven by several considerations. Conex derives from connection because this long building, covering an area of 7500 m2 connects two different parts of the city: on the east side it borders 19th century buildings located around the main entrance of Lille Flanders railway station and to the west taller buildings leading to Euralille, the city’s high- speed train railway station and its neighbourhood which has rapidly become Lille’s new business district. Since the back of the building gives on to the railway station it was also essential that the building should connect different modes of transport. At basement level an underground car park with 92 parking spaces is available for office employees and car rental companies whose offices will be located at street level. At ground level a secured cycle parking facility housing up to 550 bikes will be accessible both for commuters and office employees.
Load-bearing blades as an exo-skeleton
Along the main south facing façade new commercial premises will be created with strong pedestrian flows to and from the station. So, mobility was a strong design element. This led VS- A to design this dynamic envelope derived from kinetic art to create the illusion of movement. The building’s bold design is also linked to the round shapes of its outside walls that are dictated by road circulation inside and all around the building. The main façade runs 65 meters along rue de Tournai and is south-facing so it lends itself very well to the flowing, shimmering effect created by the building’s outer skin. By prototype testing the building a daylight analysis was carried out to determine the shape and density of these light diffusing reflectors. This analysis aims at improving the building’s energy efficiency and reaching the sustainability ratings targeted by the design team. In this case meets the building meets the stringent requirements of the French HEQ (High Environmental Quality) standard.
Between the tall window openings warm dark grey aluminium cladding makes up the inner skin of the building so as to make the bright outer skin stand out. But it would be a mistake to think this is just an ordinary outer cladding system that rests on top of the building’s structure. Each blade weighs about 20 kilos so put together these aluminium blades represent a total weight of about 20 tonnes. The blades act as load-bearing stiffeners: at the top and the bottom of each blade there are anchors set into the concrete structure that carry the weight of the blade, the metal sheet cladding and 150 mm rockwool that insulates the concrete structure. This anchor system also aims to reduce the thermal bridging. So, the whole structure can be considered more as a curtain wall or exoskeleton. When put together end by end the thousand odd sun protecting blades represent a total length of 4 kms. Each blade is made up of two elements: an L shaped supporting rod section in extruded anodized aluminium which includes one bronze coloured face of the blade. Another decorative bright copper coloured face is then screwed onto the other side of the blade which creates a visual link with the sandstone clad buildings in the vicinity.
The rows of blades on each floor are aligned on an average grid of 1.35m between each blade. Using a 3D model of the building VS-A first carried out a sunlight analysis to determine the shape, rhythm and density of these outer solar protectors. This allowed to determine the exact angle at which each blade was then digitally cut. The blades are staggered at each floor level to create horizontal perspective lines that enhance the scale of the building and allow for more elasticity in the gauging. The exact positions of the window frames have been determined by a surveyor to match exactly with the blade grid allowing for a ± 5 mm tolerance.
The houses at each end of the building are at different heights and the floor surfaces of the new building recede on the fourth and fifth floor leaving large terraced roof areas. The design of the blade system takes this into account: towards the top of the East side of the building the sun protection blades level down before rising again to form a wave-like outline at the top of the building. On this top level the blades are no longer resting on the building’s walls but on a steel posts at the base and a wave shaped steel cable structure at the top which the blades are anchored.
The building was officially launched in March of this year: it offers over 7400 m2 of office space which are now occupied by 560 employees of the Société Générale bank. Conex will contribute to the extension of Lille’s Euralille business district which now ranks third in France after Paris and Lyon.
Project facts & figures
|Design team:||Chartier-Corbasson Architects|
|VS-A: Engineering consultants:||Envelope, Fluids, Energy rating HDM: Structural engineers|
|Local architect:||François Lecat|
|Office space:||7150 m2|
|Parking space:||142 cars + 1200 bicycles|
|Commercial premises on ground floor|
|Net floor area:||7150 m2|
|Cost of building works:||13 300 000 € (excl. VAT)|
|Main building contractor:||Nord France Construction Launched: March 2018|