> The Crystal Houses façade
Cast glass, Glass façade, Glass structure, Structural glass, Glass bricks, Glass blocks, Glass engineering, Adhesively bonded, Glass architecture.
2014 - 2016
Research Team (at TU Delft)
Dr. ir. Faidra Oikonomopoulou, ir. Telesilla Bristogianni, dr. ir. Fred Veer, prof. Rob Nijsse, Kees Baardolf
MVRDV, Gietermans & Van Dijk, ABT, Siko, Wessels Zeist, Poesia
Located in the heart of Amsterdam, the Crystal Houses façade, designed by MVRDV Architects, sets a great example of the structural potential of cast glass. The new facade is an accurate yet entirely transparent reproduction of the building’s original 19th century masonry elevation. Solid glass bricks reinterpret the standard brickwork and the typical architraves above the openings, even the traditional wooden frames of the openings are translated into massive cast glass elements. As the facade ascends, conventional clay bricks intermingle in between the glass ones to create a gradient transition to the normal brickwork on the top, residential floor. The end result is a building that stands out and at the same time blends naturally into the urban fabric of the historic street.
Based on the structure of the former masonry façade, the elevation of 10 by 12 meters employs more than 6500 solid glass bricks, each 210 mm thick and 65 mm high. Glass casting was the only solution for producing glass components of this cross-section. Each brick was manually cast obtaining every time a distinctive inner flow pattern as the liquid glass solidifies, revealing the hand-made process of the elements.
The desire of the architects to attain transparency at its purest did not allow the use of any visible supporting structure, rendering the choice of an entirely self-supporting glass block system necessary. Since this was a novel structural solution, the challenge of the materialization as well as of the fabrication techniques of the solid glass block wall were assigned to the Delft University of Technology and in specific to researchers Dr.ir. Faidra Oikonomopoulou and Ir. Telesilla Bristogianni under the supervision of Prof. Rob Nijsse and Dr. ir. Fred Veer.
In principle, a glass masonry wall of the abovementioned dimensions is plausible thanks to the high compressive strength of glass and the 3-dimensional nature of the masonry wall that makes the construction buckling-resistant. Actually one glass brick has sufficient compressive strength to carry the complete dead load of the façade. The lateral stability of the glass façade was further enhanced through its geometry. Four buttresses, formed towards the interior of the façade by interlocking bricks, result in a continuous relief of increased rigidity. To obtain an all glass structural system a colourless adhesive should be applied for bonding the bricks.
The lack of standardized strength data and building guidelines for such an application of structural adhesives necessitated the research and testing on various different adhesives at the Glass and Transparency Lab at TU Delft, in order to find one that would fulfil both the visual and structural prerequisites. Actually the mechanical properties of the adhesive are equally critical to the ones of the glass blocks for the developed system, as it is their interaction as one structural unit that defines the structural capacity and properties of the glass masonry. The most favourable structural performance is when the adhesive and the glass blocks fully cooperate, allowing the masonry wall to function as one rigid unit against loading, resulting in a homogeneous load distribution.
Most adhesive candidates were discarded already in the early stages of research due to their coloration, insufficient shear strength or too high flexibility. Eventually, visual prototypes and structural tests directed the research to a photo-curing family of clear adhesives especially designed for glass to glass bonding, with high shear stiffness and good long and short term compressive behaviour. Visually, the adhesive has a similar refraction index to glass and does not discolour when exposed to sunlight. Another important feature is its photo-catalytic curing which allows for fast construction: it takes less than a minute for the adhesive to cure under UV-radiation, acquire its full structural capacity and become moisture- and water- resistant.
Series of 4-point bending tests on 1.2 m long glass beam specimens, each comprising 3 arrays of glass bricks, proved the monolithic behaviour of the system when bonded by this adhesive. All specimens acted as one single rigid unit under loading by failing with a straight, clear cut in the middle. However, the structural tests also revealed that the chosen adhesive reaches its optimum (and desired) bond strength when applied in a layer of a mere 0.3 mm thickness. The low viscosity and effectively zero ideal thickness of the adhesive together with the inelastic nature of glass generated several implications concerning its homogeneous application that resulted in exceptionally strict allowable tolerances regarding not only the brick’s dimensions but also the overall façade. Not only the size of each brick unit, but even each layer of the construction of the glass wall had to be confined within a tight dimensional precision of a quarter of a millimeter. This demand of an unprecedented high level in accuracy and transparency in construction introduced various challenges during the engineering and construction of the Crystal Houses façade, calling for innovative solutions.
The required ±0.25 mm tolerance necessitated the post-processing of the manually cast glass units: during the cooling of the molten glass, natural, inevitable shrinkage occurs to all surfaces of the glass component. After the annealing of the bricks, this shrinkage was removed from the bonding surfaces by a CNC polishing machine to provide glass elements of the desired precision.
A completely transparent wall bears yet another challenge: Any small defect in the adhesive layer, even an air bubble three meters above the ground, is entirely visible. To minimize inconsistencies in the glue layer, a special bonding technique for the uniform distribution of the glue was developed, utilizing specially designed PURE® moulds for controlling the flow, spread and amount of the adhesive.
Given the central location of the Crystal Houses façade, the system’s endurance on presumable impacts by objects such as bottles, bricks and bicycles also had to be tested at TU Delft. A hard body impact and a vandalism test were performed on an experimental glass wall to simulate accidental as well as intentional impact by small objects. Although the glass wall was able to withstand the hard body impact test, the attack by a sledgehammer caused internal cracking to the aimed brick. This suggested that a rapid impact force causes only local damage, which does not transfer to the rest of the wall. The vandalism test highlighted the importance of developing a replacement method in case of damage. Such a method was developed by locally applying high temperature to weaken the adhesive until the damaged component can be mechanically removed.
After 18 months of research, the system had been developed and proved both structurally and visually and the construction started. The nature of the adhesive required the elevation of the glass façade inside a tent to provide protection against the sun radiation, dust and the weather elements. 6 to 10 highly skilled building crew were working daily for seven months on the elevation through a strictly controlled construction process. The extremely high level of accuracy and transparency required, generated many engineering challenges during the erection of the wall that demanded the daily presence of researchers Faidra Oikonomopoulou and Telesilla Bristogianni at the site as quality control engineers. Together they controlled all 6500 bricks used in the construction and even built together with the crew the first 1.5 meter of the glass wall! As this construction is the first of its kind, new construction methods and tools had to be utilised: from high-tech lasers and laboratory UV-lamps, to slightly lower-tech Dutch full-fat milk, which proved to be an ideal liquid to function as a reflective surface for the levelling of the first layer of bricks in a precision of 0.25 mm over 12 m of length!
The Crystal Houses façade was completed after 7 months of construction and is a showcase of the great potential of the developed adhesively bonded glass brick system as an answer to the quest of structural transparency and setting the foundation for novel architectural applications.
F. Oikonomopoulou, Unveiling the third dimension of glass. Solid cast glass components and assemblies for structural applications. PhD Thesis, TU Delft, 2019.
F. Oikonomopoulou, T. Bristogianni, F. Veer, R. Nijsse, 2017. The construction of the Crystal Houses façade: challenges and innovations. Journal of Glass Structures & Engineering, 3 (1), p.87-108.
F. Oikonomopoulou, K. Baardolf, F. Veer, R. Nijsse, 2014. A completely transparent, adhesively bonded soda-lime glass block masonry system. Journal of Façade Design and Engineering, 2 (3-4), p.201-221.
F. Oikonomopoulou, T. Bristogianni, F. Veer, R. Nijsse, 2016. Challenges in the Construction of the Crystal Houses Façade. Challenging Glass 5 Conference Proceedings, Gent, Belgium.
F. Oikonomopoulou, T. Bristogianni, F. Veer, R. Nijsse, 2015. Innovative structural applications of adhesively bonded solid glass blocks. Glass Performance Days 2015 Conference Proceedings, Tampere, Finland, p.256-261.
F. Oikonomopoulou, T. Bristogianni, F. Veer, R. Nijsse, 2016. Challenges in the construction of the Crystal Houses Façade. Intelligent Glass Solutions, p.32-44.
- Talk at SHoP Architects: “The Crystal Houses Façade and the structural potential of cast glass”, NY USA 2017
- Lecture at UPenn: “The structural potential of cast glass”, Philadelphia USA 2017
- Lecture at Southern Illinois University (SIU), Carbondale: “The structural potential of cast glass”, IL USA 2017
- Lecture at The Institute of Structural Engineers: “Challenges behind the Crystal Houses Façade”, London UK 2017
- Lecture at Octatube: “ The challenges behind the Crystal Houses”, Delft 2017.
- Lecture at Van Gogh Museum, organized by Boosting: “Challenges behind the Crystal Houses Façade”, Amsterdam 2016
- Lecture, University of Cape Town, School of Architecture, Planning & Geomatics: “The TU Delft glass research group presents: Two projects in Structural Cast Glass”, South Africa 2016
- Plenary session, Inglass Conference: “ The Crystal Houses”, Warsaw Poland 2016
- Plenary session, Challenging Glass 5 Conference: “The challenges behind the Crystal Houses façade”, Ghent Belgium 2016
- London Building Center 2017, UK
- Exhibition of the Crystal Houses tested architrave
- Material Xperience 2017, Jaarbeurs, Utrecht, The Netherlands.
- Exhibition of two 1*1m prototypes for the Crystal Houses Façade.
- Dutch Design Week Exhibition 2016, Eindhoven, The Netherlands.
- Exhibition by MVRDV of a prototype of the Crystal Houses glass brick system.
- Glasstec Trade Fair 2016, Düsseldorf , Germany.
- Exhibition of the Crystal Houses tested architrave at ABT Booth and of bonded glass block specimens for the Crystal Houses at Materia Booth.
- Talent met Toekomst Nederlandse Bouwprijs 2017 (Talent with future Dutch construction engineering award) for the contribution in the engineering and construction of the Crystal Houses façade - Conjoined personal award of F. Oikonomopoulou & T. Bristogianni
- Outstanding Innovation Award 2016 by the Society of Façade Engineers
- Innovation Award in Glas Award 2016 by Bouwend Nederland
- Public Award in Dutch Design Awards 2016
- Building of the Year 2017 winner , Category: Commercial Architecture by the readers of ArchDaily
- Iconic Awards 2017 - Best of the Best winner by the German Design Council
- Architizer A+Award Popular Choice Winner 2017, Mixed Use Category by Architizer
- Prix Versailles Special Price for Exterior 2017, Shop & Stores Category
Contact (at TU Delft)