Rob Nijsse, Professor of Structural Analysis and former partner of the Dutch engineering company ABT Arnhem and ABT structural consultant Ronald Wenting were both involved in a leading capacity in the structural design for the first congenial collaboration of Rem Koolhaas and CRICURSA: the Casa da Música concert hall in Porto, the wave-shaped glass facades of which have become something of a trademark of star architect Rem Koolhaas and his Rotterdam office OMA architects over the last 15 years.
Wave-shape provides stability
Indeed, the structural benefits of a facade designed as a wave are obvious. In the same way as a sheet of paper that has been folded to form an accordion, it possesses much more rigidity than flat paper. But there are only a handful of glass bending shops in the world capable of producing curved XXL glass panes in the required qualities, with the necessary tight radii and minimal tolerances.
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The planning team also broke new ground with its solution involving the construction of the glass facade as a load-bearing, bracing element. In the case of Porto, Rem Koolhaas had the vision of glass facades without steel and where possible without disruptive pillars, beams, steel cables or frames. A considerable challenge, which was ultimately met by Cricursa, one of the world's best renowned manufacturers of curved glass. Curved XXL glass panes arranged in close proximity to each other in a wave-like design, which stabilise each other and thus jointly bear the loads acting upon them, made it possible to dispense with vertical frames.
The waveform realised by tight radii
For the Qatar National Library building for the new Education City in Doha, Rem Koolhaas also opted for a corrugated glass facade. This time the glass panes were designed in an omega shape, inspired by the notion of drying paper sheets. In a manner resembling the corners of a box being folded up, the glass facades form the shape of a diamond. They filter out the glaring sunlight and illuminate the library with as much diffuse, glare-free daylight as possible. The light is reflected down into the room via a white aluminium ceiling.
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One does not enter the 138-metre library from the side, but instead access the centre of a single triangular room under the supported corner of the building and you are immediately surrounded by three terraces with marble bookshelves. The Qatar National Library houses more than one million books and 500,000 digital editions across an area of some 42,000 square metres. A mezzanine floor with reading tables, media rooms, study rooms and a large auditorium is accommodated on a self-supporting bridge that spans almost the entire room. OMA architects Rotterdam has come across a particularly spectacular solution for the accommodation of the Heritage Collection, which comprises particularly valuable scriptures and manuscripts on Arab-Islamic civilisation and is presented in the form of a permanent exhibition: a 6-metre deep room with a glass ceiling covered with beige travertine, reminiscent of an excavation labyrinth, was embedded into the ground. The message is clear: Books are treasures that are worth raising in the public’s consciousness.
Energy-optimised facade
In the Qatar National Library, the absence of metallic elements in the glass facade additionally has a decisive climatic benefit: There are no potential thermal bridges that conduct heat into the interior of the building and which could weaken the insulating effect of the gas layer and warm edge in the curved double glazing. "Qatar is one of the regions most markedly affected by the rise in average temperatures caused by climate change”, explains Cricursa’s Marketing Director Joan Tarrus. "Outdoors, temperatures exceed 40 degrees centigrade in the summer, the temperature inside the library should be a pleasant 20 degrees. The energy-related and thus production-related challenges placed upon the facade glazing were thus enormous, especially in view of the fact we did not want to plan for mechanical shading under any circumstances. The arrangement of the curved glazing ensures the facade is self-supporting and exceptionally resistant to wind loads. Antoni Gaudí made use of the same principle when he inserted the famous Catenarian arches."
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Compared to a flat glass surface with an identical pane thickness, the corrugated shape enables much higher loads to be transferred both out of the plane of the glass – the load-bearing capacity increases by a factor of 10 here according to Rob Nijsse and Roland Weining – and also within the plane of the glass. In Doha the steel bases between the glass elements were connected with interior columns to provide the construction with even more stability.
Joan Tarrus continues: “When we started analysing OMA’s architects new challenge, undulating DGU facade, we knew there was only one way: slumping technique. Despite the technical challenges we knew we were going to face as a result of the extreme climate conditions in Doha, curved annealed glass was the only possible approach to provide an integral solution (geometry, coatings, ceramic frit, dimensions) corrugating the glass to 550 mm radius, providing us with greater freedom in the design process.”
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The glass panes that are up to 5.50 metres high, laminated and curved, are designed as double-glazed IGUs. A low-e coating, and a solar control coating, filter and reflect sunlight. A grey grid of 3 mm metallic dots with a precise 6 mm spacing between them was burnt into them in order to reduce radiation transmission even further; it represents a technological masterpiece due to these tight radii and the immense sizes involved.
Warm Edge indispensable in desert climes
Cricursa chose the Super Spacer TriSeal Flex product as its warm edge spacer. The product developed by Edgetech/Quanex especially for curved glazing is, based on the experiences of Cricursa, ideally suited for the extreme climate loads in the desert.
Edgetech
"In this climate region, the use of a warm edge for double glazing is indispensable in order to optimise the energy efficiency of a building," explains Joachim Stoss, Managing Director of Edgetech Europe GmbH and Vice President of International Sales at Quanex. The constant transition between hot sunlight, shade and cooler night temperatures leads to the permanent movement of the glass, and consequently, to considerable mechanical stress on the edge seal. "Flexible spacers such as Super Spacer hermetically seal the space between the panes for many years. Due to the properties of the structural foam, the spacer system absorbs the pumping motions of the panes and prevents wear of the primary seal,” Joachim Stoss explains.
