A few weeks ago, Nick mentioned that a contact of his, Chris Matthews, a structural engineer from Atelier One, may be a useful person for me to talk to about my project. Nick got in touch with him and Chris very generously agreed to speak with me over Skype. I sent him a curated selection of my work over email ahead of this, relating particularly to the issues that I have most technological questions on at this stage, and now we have just had the conversation.
About Atelier One
Atelier One is a British structural engineering company established in 1989. They have collaborated with architects, designers and artists, and have been engaged in a number of unique, experimental projects.
Architecturally, notable projects include Gardens by the Bay in Singapore, Chadstone Shopping Centre and the Ljubljana National Stadium and Arena – all of which are examples of complex roof geometry engineering.
Outside of architecture, they've also collaborated with artists such as Anish Kapoor and Rachel Whiteread, touring and non-touring stage shows, and the opening and closing ceremonies of the 2012 olympics and 2014 winter olympics.
Atelier One are an engineering firm that I am very lucky to have been able to have contact with for a couple of reasons. Firstly, they have experience of casting and using concrete in novel ways, such as in Rachel Whiteread’s House. This expertise is useful to me for discussing the specification and application method of the concrete and suggesting alternative cast materials. Secondly, they also have direct experience of working with bamboo as an architectural and structural material, which is rare for UK based companies. Their website has already been a resource that I have used in this capacity.
Screenshot from ArchDaily article on bamboo referencing Neil Thomas, director of Atelier One
Points of discussion
We managed to cover a lot of ground over the course of our conversation, with Chris giving me a better understanding of some things that I had already done some research into, as well as introducing some new ideas for me to think about. The key things discussed were as follows:
The proposal is using bamboo to its best structural advantage:
Chris explained that my proposal takes advantage of bamboo’s best structural qualities. Bamboo is very strong with forces parallel to the culm, due to the dense fibres all running in this direction. These fibres are the ‘vascular bundles’, which carry water up and down the culm, and are what give it its stiffness. By evenly loading many bamboos axially in this way, I am loading it in its most efficient way. This contrasts with if the bamboo was cut and used more conventionally, where pins may be put through it for connectors, which split apart the fibres and weaken it, and where bamboo culms will not all be being axially loaded.
Atelier One lecture slide demonstrating bamboo's natural strength and stability
Dome-like overall forms are beneficial:
Domes and arches are structurally efficient, acting purely in compression, and therefore require no reinforcement. The smoother the curve of the dome, without any kinks, the more efficient and fully in compression it will be (any kinks deviating from the smooth curved line of force will result in bending forces, which then necessitates reinforcement). Ideally, domes that aren't too shallow should be used, as otherwise there are large lateral forces at the base, pushing outwards.
Mitigating section depth issues:
Chris thought that the ‘soft pillow’ forms that the cast material makes in between the bamboo supports do not pose a structural issue, providing that there is sufficient depth behind the indentations. In other words, the ratio between the minimum depth of the structure at the indentations compared to the average depth or the maximum depth cannot be too great.
The need for bracing the bamboo:
To counter the horizontal forces when the fabric is stretched over it, Chris agreed that some sort of bracing would be required, and that tension rings are a good way of doing this. Bamboo is very flexible, so without this, it will bend under the force of the fabric stretched over it.
‘Over-engineered’ use of bamboo – much stronger material than needed for this application:
Chris noted that using the bamboo in the manner proposed means that it is much stronger than would actually be required for loading it with the cast material – he estimated that probably only 5-10% of each bamboo culm’s strength capacity would be used. This is not a problem – if anything, it shows that this method will definitely work and not be on the borderline of failure in any way at all. I am proposing that the bamboo will be used more in more conventional structures in its second life function, which is where its strength will be particularly required.
Strength vs speed of growth compromise:
Prior to discussing with Chris, I had been unclear on how long it took for bamboo to grow for construction use, as some sources seemed to indicate a matter of months whereas others suggested that it was a few years. Chris clarified that bamboo will grow to its full height in between half a year to a year, but will not then reach its full strength until about three years after planting. For my project, this means that I could be using the bamboo as formwork for casting in half a year to a year, but then once the bamboo is cut away it wouldn’t be of much structural use. If I am wanting to use it in its first and then second life, I will probably need to wait three years before casting on top of it.
Possible application method/material – 'Concrete Cloth':
One of the main questions that I had for Chris was for his suggestions on how to cast concrete onto the forms that I am proposing. One idea that Chris introduced to me is 'Concrete Cloth'. At first glance, the main positive seems to be its ease of application, as it is simply laid where required and then water is sprayed onto it. Some of the negatives for trying to use it in my project are its lack of flexibility, and the environmental issues of it using cement and PVC. However, this is definitely a useful material to look into further, and perhaps I can propose a related alternative which addresses these two issues.
Concrete cloth close-up and put to use to create a shelter
Alternatives to cement, for environmental reasons:
Another key question that I had, alluded to in the previous point, was regarding viable alternatives to cement for use in my concrete. Chris mentioned fly ash, which I was aware of, but also told me about GGBS (ground granulated blast furnace slag), a by-product of producing steel. These are both options which I shall now go and research further.
Origins of GGBS – (top left) blast furnace, (top right) molten slag, (bottom left) granulated slag, (bottom right) GGBS
Reflection
This was an incredibly informative conversation for me, and I am very grateful for Chris taking time out of his day to share his expertise with me. I feel reassured by what we discussed, as Chris didn't identify any major stumbling blocks or issues with what I have been proposing up until now.
The new ideas and options for various parts of the process will be a good starting point for informing parts of my Technology DSIT C work, and I think it will be good for me to properly research and weigh up the pros and cons of each option within this report, before concluding which strategies I will be taking forwards.
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