Housing over a million books including ancient Arab-Islamic manuscripts, Qatar’s National Library in Doha is a haven for culture, research, study and collaboration along with some of the most important and rare texts in the Middle East.
Dutch architecture studio OMA designed the monumental building, inaugurated by their Highness’ the Sheikh and Sheikha of Qatar in 2018. The library, commissioned by the Qatar Foundation, plays a central role in Education City, joining acclaimed research facilities and invoking a great sense of historical pride and belonging in the Arab world.
The corrugated-glass façade – a structurally robust system developed with Pritzker Prize laureate Rem Koolhaas and the team at OMA – insulates library visitors from the harsh Qatari climate, filters the bright natural light and creates a tranquil oasis in an otherwise challenging environment. The result is a visually stunning façade for a building of national significance which showcases the potential of laminated annealed curved glass.
Structural potential of annealed curved glass
The Qatar National Library designers faced a common challenge to glass design ambition; the structural response to building loads. Where the characteristic strength of annealed glass approaches its limit under specific project conditions, specifiers will turn to heat strengthened alternatives such as tempered/toughened glass, which have a higher material resistance and rule out the option of annealed glass, which enjoys more design freedom.
In the case of curved glass, we can benefit from the unique characteristics of curved surfaces – the geometric stiffness can provide structural robustness that would otherwise prohibit use of annealed glazing. Structurally, the same theory applies to the famous catenary arches of Catalan architect Antoni Gaudí (1852 – 1926).
The corrugated-glass façade system developed with OMA for the Casa da Música in Porto, Qatar National Library and since then, Taipei Performing Arts Center, features curvature profiles of tight radii in close proximity of one another – in this case “omega” shaped – which provide robustness and offer an engineered solution to the use of annealed glass. The curved form, paired with the added features of lamination, can meet structural capacity and safety requirements while offering a world of design possibilities.
This principle extends to the support conditions, where the perimeter framing supporting each glass unit has been reduced from all four sides, to just two-side supported – along the top and bottom edges of the panel. Aesthetically, this means that vertical support members, or mullions, do not interrupt the viewing experience of the onlooker.
The absence of vertical lines fosters visual continuity between the inside and outside environment of the library – an invitation to experience the building and surrounding urban space with the engineered transparency that only glass can offer.
Curved glass in extreme climates
Already one of the hottest places on Earth, Qatar has seen average temperatures rise more than 2 degrees Celsius above pre-industrial times. It is the fastest warming region on the planet after the Arctic. The average summer day commonly tips over 40 degrees and in a July 2010 heat wave, the temperature hit an all-time high of 50.4 degrees. Facing the unbearable heat, Qatar has begun to air-condition the outdoors.
The global climate conditions are demanding high-performing façade systems which contribute as an important tool in a building’s armory of embodied and operational energy features.
To manage a temperature of 45 degrees outside and maintain 20 degrees inside the library, the laminated and insulated curved glass assembly is comprised of a low-e coating, a ceramic frit pattern and a solar control coating. The glass also underwent specialised thermal stress analysis – the temperature of the outer glass reaching up to 70 degrees in some instances.
The ceramic frit pattern is made up of metallic grey dots with 3mm diameter printed precisely, 6mm between dot centers in a staggered distribution for low heat absorption.
Low-e and solar control coatings engineered to manage incoming light filter and reflect sunlight to reduce the heat transmission through the glass unit considerably, maintaining pleasant natural light ingress.
How do the curves help? As an advantage to thermal performance, fewer metallic framing members also reduce the ‘bridge’ between ambient outdoor conditions and the controlled internal environment. This bridge can be understood as a transfer of heat through a window, which is limited by the air cavity in insulated glass units, but compromised by metallic properties of the framing system, as metal conducts heat.
Eliminating framing reduces heat transfer, which in turn reduces the energy required to maintain the building’s thermal comfort systems.
Tight radii and associated complexities
The radius of curved glass is commonly used to express the extent of curvature. The lower the radius, the tighter the curve. Using conventional tempering ovens, a radius as low as 700mm can be achieved without compromising architectural optical quality. Below this limit, entering the world of annealed, slumped glass has seen curves with radii as small as 200mm – see the 40 Bond St Apartments in New York City by Herzog & de Meuron.
Qatar National Library’s “omega” curves have radii of 550mm and over in Taiwan, Taipei Performing Arts Center’s “S” shapes curve at 330mm. Laminated, insulated glass in large dimensions is complex – include tight curves in the mix and you have quite the design and fabrication challenge.
To make annealed curved glass, a flat panel is heated up to 600 degrees Celsius and slumped over a hand-made mould. The high temperatures can easily damage coatings and more complex forms or smaller radii introduce further complications – you are working with glass transitioning to a near-liquid state. When the target curve profile has a small radius, limitations in glass thickness need to be considered. Smaller radii are better achieved with thinner glass as it weighs less on the mould and has a lower sectional capacity, meaning it can be manipulated with more flexibility. In this façade, the glass panes are 8mm thick.
Few manufacturers in the world can do this, and Cricursa has spent over 90 years combining artisanship and innovation to perfect the craft. Last year, K11 Musea in Hong Kong opened to the public; a building lined with over 380 laminated glass tubes which tower at 9m high and measure 450mm in radius.
New decade, new possibilities in curved glass
Designers of the built world continue to demand flexibility in design – to push what is possible in building materials. Above all, glass offers transparency and can connect spaces with communities by offering visual continuity between inside and outside, here and there.
In 2020 and beyond, size continues to be a key factor – architects can play with scale and connectivity more than ever. Cricursa made their name as pioneers of “XXL” curved glass, which over the last decade reached up to 10m high. Today, Cricursa has the capacity to create curved, tempered glass 18m in size.
But size isn’t always everything. With a continued commitment to partnering with and enabling designers and specifiers, more options, especially in tempered glass, are on offer. Bending in two directions, i.e. spherical shapes, can now be manufactured in tempering ovens where before this has been achieved only with the slumping method. There is more flexibility in terms of convexity as well; new ovens mean coatings can be applied to either surface of the glass and are not governed by the orientation of the curve.
An expansion of facilities through the acquisition of two new factories in Catalonia means that quality flat glass processing capabilities join the Cricursa arsenal, responding to clients who want volume, both flat and curved, in exceptional quality. The additional space houses new, large processing equipment for both flat and curved glass, meaning Cricursa can deliver range: from high-rise structures to boutique façades.
Designers are shaping the built world to address the social, climatic and technological challenges of the next decade. Glass in the context of materiality and space continues to be a tool to foster interconnectivity in communities, wellbeing in building occupants and beautiful architecture. In the case of Qatar National Library, it creates a light wellspring in the desert connected to an educational campus, democratising knowledge and conserving Arab-Islamic cultural heritage.
This interview was originally published in IGS Magazines Spring 2020 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Joan has been a fundamental part of Cricursa for almost two decades. Partnering with architects, engineers and façade contractors from design conception, his innovative “Yes!” attitude has been intrinsic to shaping some of the most iconic buildings in the world. After studying Industrial Design and Marketing, he worked with specialist façade contractor Bellapart in Catalonia, with whom Cricursa collaborated on Heatherwick Studio’s memorable Bombay Sapphire Distillery in Laverstoke UK. Now Cricursa’s Director of Marketing and International Business Development, Joan has been responsible for projects such as the 40 Bond Street Apartments by Herzog & de Meuron in New York City, Taipei Performing Arts Center by OMA, SANAA’s undulating La Samariaine in Paris and the famous 9-metre Vidre-Slide created for Glass Technology Live 2016 with Eckersley O’Callaghan Engineers. It is safe to say Cricursa’s advancement over the past 20 years would not have been possible without him.