There’s something to curves, circles and cupolas – round shapes as such – that are striking; they seem to be embedded in our DNA. From measuring the human scale, organizing common dwellings to covering large spaces, “odd” round shapes have become, most probably, more prominent than “regular” squares.
Despite all surrounding myths and construction methods, round shapes seem to best fit our perception of a shelter; they define space – unlike the confining nature of flat walls – they cover and embrace. Even in contemporary architecture and in a time where building materials have been modernized, the design attitude has not changed. Furthermore, the emancipation of load bearing (iron, steel) structures and attached (glass) façades led to – in its truest meaning – the “building envelope” or “building skin”. Walter Gropius’ Factory Pavilion at the Werkbund Exhibition 1914 in Cologne, Germany, or Ludwig Mies van der Rohe’s scheme for the Friedrichstrasse Skyscraper in Berlin, Germany, 1922 represent best this new embracing of transparent curves.
But how do we create curved shapes? What are the principles behind it? And why is it (again) so ‘en vogue’ in this day and age?
This is basic geometry: Divide any flat (glass) surface into triangles, “upfold” them and enlarge their sizes to the point where they can be joined again according to the larger designed curved shape. These shapes are created through the supporting structure and not through the filling (glass) panels. Projects like Frank Gehry’s DZ Bank, Rudy Ricciotti’s extension of the Islamic Arts Collection at the Louvre’s Cour Visconti and Norman Foster’s famous Gherkin are breath taking examples of this geometrical method. Let’s also not forget more recently, the spectacular roof of the Heartspace of the University of Sheffield by Bond Bryan Architects and Renzo Piano’s Sphere of the Academy Museum of Motion Picture. All of these innovative projects feature glass by Saint-Gobain.
The Gherkin © Robert Bauer, Wikimedia commons 
©Heartspace. Photo by John Kees 
© Renzo Piano Building Workshop, Academy Museum Foundation 
Extension of the Islamic Arts Collection ©Tangopaso, Wikimedia commons 
DZ Bank ©Spielvogel, Wikimedia commons
Cold bending
The oldest form and method of glass bending. In cold bending or assembly bending, the initially flat glass is formed by forcing it into or onto a curved substructure. Thus, the shape of glazing is maintained by a permanent mechanical fixation onto the substructure. Consequently, the restoring forces introduced by the glazing into the substructure must be taken into account during the initial design phase. The permissible bending geometry depends on the residual stress permanently generated onto the glazing and likewise the viscoelastic properties of the laminated film used. In short: this technology depends on the thickness of the glazing (mono as well as laminates) and the expertise of the glass processor and installing company to do the job accurately. There are limitations using the cold bending method in that only large radiuses can be created.
Frank Gehry’s cloud like IAC headquarters in New York is not only an iconic building, but one that best displays the capabilities of this technology. It is also noteworthy that this was the first building by Gehry with a complete glass facade. The approximate 1,437 glass panels lining the facade, of which 1,349 are uniquely shaped with varying ‘degrees of twist’, were manufactured by former Saint-Gobain Glassolutions Sas van Ghent. The white color of the glass is a result of bespoke ceramic dotted patterns to the purpose of reflecting light and reducing glare.
Hot bending
Using this method, the flat glass is heated in a furnace over a mould. After the glass has sunk into the mould under its own weight, the furnace is cooled in a controlled manner, minimizing thermal residual stresses. This process is also suitable for laminated safety glass, as here, panes can be bent in pairs using special release agents. Even isolation glass units can be put together from individually bent glass sheets.
With hot bending, complex geometries like cylindrical curves (single radius), elliptical curves, irregular shapes (e.g. S-shapes), tangential extensions (also asymmetrical), multi-radial shapes, and spherical shapes with small radiuses can be realised in sizes up to 3,100 x 16,000 mm – depending on the machinery of the glass processor.
In any case, the knowledge and capabilities of the glass processor determines what will be possible and at what cost. A consultation early on will help designers to find the right approach. At the last glass technology live in 2018 we all bore witness to what these specialized glass processors are capable of. One of the stand-out exhibitors demonstrated the potential of hot bending with an 8-meter-long glass tunnel produced by Saint-Gobain Glassolutions Glas Döring in Berlin.
Below are some astonishing projects that demonstrate the potential applications of curved glass:
Quai Quest, Bologne-Billancourt, France
Atelier d’Architecture Brenac & Gonzalez et Associés, Paris, France
Laminated curved glazing STADIP® CONTOUR® SOLAR
Kistefos Museum, Jevnaker, Norway
BIG Bjarke Ingels Group, Copenhagen, Denmark
Building 026 Arnhem, The Netherlands
V8 architects, Rotterdam
Curved low-e double isolation glazing unit CLIMAPLUS® CONTOUR® PLANITHERM XN II
Hot bending during the thermal toughening process
Cylindrically curved glazing can be produced from thermally toughened glass. The production process is similar to that of flat toughened safety glass. The glass is first heated in the furnace area (above the transformation temperature) and then moved to the cooling area where the bending equipment is integrated. Using this method, the conveyor rollers can be adjusted to the cylindrical bending shape after the hot glass has been moved into the cooling area.
The glass is subject to oscillating movements in the shaping cooling area to form the cylindrical shape. These advances in glass processing allow for curved glass solutions where safety and security performance are a priority.
Refurbishment of Vienna Underground Entrances, Vienna, Austria
Hans Hollein, Vienna, Austria
P2 Urban Hybrid, Innsbruck, Austria
LAAC Architects, Innsbruck, Austria
Fondation Louis Vuitton, Paris, France
Frank Gehry, Santa Monica, United States
Laminated curved glazing STADIP® CONTOUR® DIAMANT
The production of curved glass is tricky to say the least so here are a few points you should be aware of:
- Due to technical restrictions, solar control coatings, thermal insulation coatings, enameling/fritting, screen printing, digital printing are located on the inside of the bend (concave side).
- As a result, pay attention when designing S-shaped facades with IGUs.
- Geometry always refers to the outside of the curve (convex side).
- Currently, light, energy and acoustics performance data cannot be calculated specifically for curved glass due to technical limitations of the software. All values provided are usually calculated for flat glass and vertical mounting.
When undergoing a project, it is essential to be prepared and discuss the required performance and aesthetic needs with the glass processor in advance. The curved part of a façade may be small in terms of square meterage but may have a significant impact on the entire layout of the building envelope. Parametric design does not only take into account formal design aspects, but curved glass allows a marriage between function, performance and beauty – a relationship that Saint-Gobain would like to help you build.
For any assistance, please contact us at glass.facade@saint-gobain.com.
For other inspiring projects, please visit: https://medias.im.saintgobain.com/ebooks/Internet/glass_for_facade_2020
This article was originally published in IGS Magazines Spring 2021 Issue: Read the full Magazine here for more thought-leadership from those spearheading the industry
Author:
Andreas Bittis, International Market Manager at Saint-Gobain Glass, BU Facade
Educated as an architect and urban planner at the RWTH Aachen University in Germany, Andreas Bittis was editor for ARCH+ and a freelance journalist for various architectural magazines on and offline. Consequently he worked in several architectural practices; Rhinescheme (Beijing) ingenhoven architects, (Dusseldorf, Sydney, Singapore) and Eller + Eller Architekten (Dusseldorf, Berlin, Moscow) to name a few, as project manager in different domains. With this background he joined Saint-Gobain Building Glass in 2012 as Architectural Specification Manager working not only on advising architects and façade consultants but also on topics like Sustainability and BIM. In 2015 he joined the German marketing team as Product Manager for all coated glass and Market Manager for the glass façade projects. Most recently, Andreas joined the Business Unit Façade as Market Manager in Paris