A car swinging upside down suspended only on two sheets of super-thin glass: ‘Gravity’ is a collaboration between engineers, architects, fabricators and suppliers showcasing the technological advances in glass processing, adhesives, high precision engineering and manufacturing. “Gravity” is a demonstration of a highly innovative, efficient and aesthetic design.
The bold idea of ‘Gravity’ was conceived by us at Define Engineers and creatively enhanced by Carpenter | Lowings’ architectural input, which resulted in an outstanding realisation by Seele’s manufacturing excellence. Two sheets of thin glass elegantly bonded to stainless steel edge strips are suspended from a tripod structure which holds the swinging car tantalizingly close over a podium. The glass sheets are 1m x 2m, composed of two 2mm heat-strengthened laminated glass panes. This visually and physically light structure without mechanical fixings impresses with its load bearing capacity.
The dramatic image of a swinging car was inspired by a sculpture I saw at the Burning Man Festival in 2017 in the USA where I took some students to make an art installation in the desert. The sheer drama of using a hanging object to display the force of gravity was a gripping moment of realisation for me. Naturally, being a structural and glass engineer, I asked myself the question “What if we can hang an object on very thin glass?”.
The notion of the car came about while I was visiting the research team at TU Delft Architectural Technology department, headed by Prof.Ulrich Knaack. He was heading up the organising committee for the 2018 Glass Technology Live for Glasstec and was on the search for inspiring ideas involving glass. Ulrich liked the idea of the car as a fun interactive way to showcase advances in glass and bonding technology. We saw this project in the category of fun but useful examples of technology inspired by Lisa Rammig’s Glass Slide.
Thin glass has, over recent years, been enhanced technically by the development of strengthening processes such as air-toughening and the awareness of Gorilla and Willow glass which are formed avoiding flaws which originate from contact with the molten tin of conventional float processes. At the same time bonding systems like TSSA from Dow have begun to suggest different ways of getting forces in and out of glass surfaces: previously with thicker glass systems minimisation of fixings meant development of point fixings, which of course focus forces at the points. Thin glass in turn suggests that a more distributed fixing system would be necessary, and a strip fixing has a lot of potential in this scenario. In a car windscreen for example, thin glass suggests a continuous perimeter fixing rather than point attachments. This has significant and interesting aesthetic merit which has been a direction of exploration by glass designers for a while.
Technically we as engineers were excited by the prospects, as the true structural implications of working with thin glass are only entering the consciousness of engineers. The advantages of using thinner glass are obvious in terms of weight, energy and transport cost savings but the aesthetic and technical challenges are still being understood. We as a team were gripped by the potential of this. Ultimately, the project proved a really interesting test-case and illustration of how innovation and change take place in the construction industry.
The key to the success of this story should be primarily attributed to the excellent team that worked very hard for nine months to turn the project to reality. We floated the idea approximately a year before Glasstec to Carpenter | Lowings (C|L) being impressed by their design ambitions which always resulted in spectacular architecture. We knew an idea as simple as hanging a car upside down requires meticulous attention to detail and proportion as well as careful thinking about human interaction. After all, realising simplicity is the ultimate challenge. We reached out to Luke Lowings naturally as someone who had completed a number of innovative and dramatic sculptures involving glass and steel. Having explored thin glass before, Luke and his team were inspired by the potential of the car project as a way of gaining more insight into the problem. For (C|L) the aesthetic component was the driver, working for almost thirty years in sculptural and architectural use of glass, this project seemed a natural extension of other aesthetic preoccupations with light, reflection and structure.
A few months later, Define and (C|L) approached Seele with an image for the hanging car. As the leader and innovator in the glass and steel industry, we knew they had the necessary mindset, technical resources, know-how and bravery to execute such project. Luckily, Seele were on the lookout for a good demonstrator for Glasstec and agreed to support the project. Luke and I had worked with Seele on a number of interesting projects recently and the beginning of the project brought familiar faces, notably Martien Teich (head of R&D), Holger Krueger (Head of Design) and Andreas Hafner (CEO). This trusted and well-connected group in London and Gersthofen formed the core of the design team with connections in Finland, the USA and Bulgaria, developed the design over about nine months entirely via video conference calls, nibbling at the edges of convention, always verifying the structural issues, but also willing to think outside the box. The dynamic on a project team like this is very interesting.
Contemplating with Luke at C|L, “The drama of the concept forms a literal and metaphorical focal point for the group, and this human need for ‘something interesting to do’, while it might seem trivial, is actually one of the most critical drivers of innovation. Often this ‘something interesting’ is working on a large or prestigious project, but it doesn’t have to be, because often procurement systems mitigate against risk or ‘one fabricator’ solutions which of course limit the advantage of an innovative supplier to offer new ideas.” An innovation prototype is a successful model due to its relatively low financial risk environment. So the project became an interesting way of testing something that doesn’t require massive investment but provides a dramatic demonstration.
Once the team was committed, it was time to get to work and go through the stages. An iterative design process took place throughout the project, with design concepts (Define/ C|L/ seele), structural sizing (Define), 3D architectural modelling (C|L), detail engineering (Define) and final fabrication design, manufacturing and testing (seele). Seele was responsible for the preparation of the car as well as the design and manufacturing of the suspension points on the vehicle and the installation of the tripod and car structure, with over 20 members of their engineering, production, installation and PR teams.
The team at Define relied on state-of-the-art engineering methods to determine the behaviour of the 1.5 tonne car pendulum as it swings. A simulation called Non-linear Transient Dynamic FE analysis captures the hanging and dynamic nature of the system, the results of which are used to design all components of the exhibit. The thin glass stretches under the dynamic 15kN load, which eliminates all bending and ensures the glass behaves as a membrane – the most efficient way to carry load.
The idea that the car would swing was integral from the beginning. To keep things simple, we envisaged attaching the car to the ceiling but the Messe building is not designed that way, so we had to design a special structure to hang it from. Luke and his team proposed the simple tripod structure – echoing the triangular form of the glass arrangement and raising it off the floor to make the gap under it more apparent. They approached TriPyramid Structures who agreed to design and fabricate the hanging rod and bearing assembly which allows the free rotation of the car in any direction avoiding bending stresses in the glass, with one 9.5mm rod supporting the entire car. The hangers and all brackets are carefully designed to avoid out-of-plane forces bending the glass, and the pivot at the top has been specifically designed for this project to allow maximum movement and minimum friction to reduce twisting forces in the glass planes. The heat-strengthened glass is bonded using Dow TSSA to stainless strips within the hanger details which are in turn connected to the car and the specially designed and fabricated suspension detail at the top.
The laminated glass uses SGP as an interlayer, and the glass, being heat-strengthened, has a breakage pattern which allows transfer of loads to the back-up glass sheet, through the interlayer. Note that the detail is one-sided to reveal the transparency of the fixing detail and preserve the clarity of the front face of the glass. This suggests how it could be presented in an architectural context for real projects. A key feature of project is the transparent connection between the glass and the stainless steel brackets made with The Dow Chemical Company DOWSIL™ Transparent Structural Silicone Adhesive (TSSA). The permanent stress in the TSSA layer, estimated at about 0.6 N/mm², is further increased by the dynamic effects of the swinging car to ~0.7 N/mm². Seele carried out structural performance tests to confirm the TSSA reliability utilising samples of thin glass with a size of 400 mm x 600 mm provided by Glaston Corporation. The test TSSA bonding area of 300 mm x 40 mm had to transfer a permanent load of 4.5 kN resulting in local peak stresses of about 0.6 N/mm².
The short- and long term tests were successful with an ultimate load capacity of 53 kN. Ultimately, this collaboration is a demonstration of how innovation can take place in the glass industry. Now more than even, we need an open industrial environment of technical innovation in which ideas can cross-fertilise and can be recombined. In a highly-litigious and intellectually protective environment these notions cannot flourish. We hope the project inspired and sparked new avenues of thought of how we as an industry can move forward and make things better.
• The tripod and podium were fabricated in Bulgaria by BSYS, Ltd.
• The bonding material was provided by Dow, along with technical advice and financial support.
• We asked TriPyramid Structures for technical and design advice for the central pivot detail. They were kind enough to provide their knowledge and also fabricated the actual components (and supported the exhibit financially).
• The glass was supplied by Glaston of Finland, fabricators of glass processing equipment who were able to supply thin heat-strengthened sheets of glass.
• The glass lamination with SGP was carried out by by Sedak.
• We thank Dr.Robert Akerboom for his kind support during the process as part of the organising team.
• Car = 1200 kg + 300kg counterweight in boot;
• Glass = 50kg (incl. interlayer)
• Glass build-up: 2x 2mm Heat-strengthened, SGP-laminated; 1950mm x 985mm
• TSSA Bonding area: 6 x 0.30 x 0.04 = 0.072 m² TSSA per panel
• Load in each glass panel and TSSA bracket: 1 380 kg
• Breakage capacity of: glass panel = 10 850 kg
• Breakage capacity of TSSA per bracket = 53 000 kg
• Frictionless 360° spin and max 15° swing of car
• Car make: Fiat Coupé, type 175, 1.8 16V, 1990s
• Collaboration of partners across 7 countries
This article first appeared in IGS Magazine’s Spring 2019 Issue – Read the full Magazine here for more thought-leadership from those spearheading the industry
Vlad is a specialist chartered structural engineer and co-founder & director of Define Engineers. He is regarded as one of the key designers and innovators in the special structures field and has designed and delivered a number of award-winning projects world-wide. Vlad enjoys collaborating on highly challenging briefs which involve first principle thinking combined with rigorous analytical approach.
Educated and operating out of London, Vlad has worked for a number of household names in the building engineering industry and most recently as a leader of the structural glass team at Arup in their headquarters in London. Vlad is currently a honorary lecturer in Civil Engineering at Imperial College London and teaches materials at the Architectural Association, London. He believes in research as a key driver for success and is closely involved at all levels of academic research both in Imperial College and Cambridge University.