Custom-designed components for the Crystal and the Cloud: optimising a free form

Requiring about 650 t (1.4 million lb) of steel, the Crystal is made up of 32 differently sloped sections curved at different angles. The primary and secondary steel structures are connected by an innovation system developed for the project. In order to ensure a uniform aesthetic and prevent any gaps in the connections on account of the complex geometry, an ad hoc system was developed that conceals the connection points but also meets static requirements.

Supported by the primary structure, the Crystal’s glazed envelope is made up of panels of extra-clear glass connected to a secondary - 180 x 80 mm (7 1/8 x 3 1/8”) - frame with the same innovative system used to bolt the outer and inner structures together. The technical challenge here lays first and foremost in the way the structural steel mesh was to be connected to the large glass panes without putting excessive pressure on the glass.

For the first time also flush ventilation windows and natural smoke and heat exhaust ventilators (type NRWG) were developed. Over 200 windows with sizes of 2.6 x 1.5 m (8.5 x 5 ft) were designed, manufactured and tested regarding permanent functionality, air and water tightness. In addition all fire protection tests were carried out which were necessary to achieve the European approval as NRWG ventilators.

The side façades have a brise soleil sun-shading system that also ensures acoustic protection. The sun-shading elements are managed by a building automation system built into the steel structure, as indeed are all the connections, wiring and plant, with the result that everything is out of sight.

Functional and decorative elements were developed for the Cloud, alleviating the imposing solidity of the steel-clad structure. Eleven sub-areas of the opaque envelope are glazed and provide natural daylight in the museums rooms. The laminated glass is acoustically insulated and permeable to light, thereby reducing the need for artificial lighting on the interior.

A striking feature of the Crystal, and a highly complex part of the whole project, is the so-called Gravity Well. This cone shape structure starts with a depression in the roof to then plunge down, tapering as it goes, to the floor of the atrium below. Along with its considerable aesthetic impact at the entrance, the sinuous glazed cone measuring 33 m (108 ft) also serves an important structural function, reducing the weight of the overall steel structure by around one third. It is a real distillate of design, technology and innovation. Essentially, it is a tapered cone made of triangular-shaped laminated glass with an integrated silicon water drainage system, whose main drainage channel runs along the steepest side of each triangle (the other two sides contain secondary drainage canals). The Gravity Well’s structure was optimized using advanced 3D software. Together with the architects, the engineering teams designed some 160 one-off connecting nodes to connect the various structural components. Producing the glazed segments also proved an arduous task. Each single element had to be heat bent to a wide range of curvature specifications. The lower section of the Well that reaches into the Museum hall is made of curved glass panes glued to aluminum profiles. The four lower units have a curvature radius of less than 500 mm (19 3/4”), similar to the windscreen of the cockpit of a small airplane. But bending 4.5 m (15 ft) architectural glass panes as in this project was no easy feat. The Gravity Well ends in the so-called ‘Lens’ (la Lentille) made up of two semi-circular self-heating panes of laminated glass. These heat sensitive panes ensure any snow accumulation melts quickly. They are also activated by a system that when necessary automatically brings the surface temperature to +5 °C (41 °F). Some glass segments can be opened, allowing for cleaning of the surface of the lens and lower cone.