About a month on from having a discussion with Chris Matthews, I've now had the opportunity to run my scheme past another engineer, Peter Corbett of Corbett & Tasker. This was great, as it meant that I could ask for his input on some issues that had arisen in the time since I spoke to Chris.
Regarding materiality, as well as mentioning GGBS and fly ash as partial substitutes for cement in the concrete, Peter brought the product 'Cemfree' to my attention. This is a product which enables to be created completely cement-free, as the name would suggest. This is an improvement on the other options, which can only be used as partial replacements. This is something that I now need to investigate further, but unless there are any surprising drawbacks or limitations arising from the specific way that I am intending to use it, I imagine that this could be the solution to the cement issue. On a related note, Peter pointed out that for the forms that I am suggesting and the loading that they will be under, it only needs to be a fairly weak concrete mix
Extract from the Cemfree brochure, extolling its sustainability credentials
After asking about materiality, I asked about the section depths that might be required for my cast forms, provided that I work only with compressive domed and vaulted forms, as I agreed with Chris. Peter said that he reckoned that between 75 to 100mm may be possible. He noted that flatter areas will be weaker, so to avoid them where possible – this adds into the advice that Chris gave me about not having domed forms that are too shallow. Peter mentioned that an anti-cracking membrane or strategy of some kind should be used, and mentioned that bamboo reinforcement is something which is being investigated currently. Peter also suggested that I look at the work of Felix Candela to find examples of spans similar to those that I am trying to achieve, and then base the thicknesses off Candela's equivalent spanning structures.
Two examples of Felix Candela's thin shell architecture – Los Manantiales (left) and Club Nocturno La Jacaranda (right)
Something which I hadn't discussed with Chris at all, due to it not having developed as part of the design at that stage, was the possibility of having opening in the vaults, oculi for allowing light in or larger openings to become full courtyards. This is something that occurred to me a few days ago, but I was unsure if this was possible or if it would simply render the vault or dome to be structurally compromised and liable to collapse. I was happy to hear Peter confirm that this would be possible and didn't pose any major issues. He did point out that where doing this, though, it would be necessary to stiffen the lip, as he told me that shell structures can be weak at their edges. He gave me a precedent study for this – the Pines Calyx. This is actually made from rammed earth, but has a substantial opening at the top of its dome, with an upstand that stiffens the whole structure.
Pines Calyx, showing the oculus with its upstand
A final point of discussion that we quickly had before Peter had to go to his next appointment was on the subject of creating temporary structures out of the bamboo for its second life function. For this, Peter pointed me in the direction of the work of Taiwanese artist Wang Wen-Chih, specifically his installation 'Woven Sky' from Woodford Folk Festival, Australia, in 2014. I do think that this idea of weaving bamboo could be a good one to explore, enabling structures to be created with few other materials required.
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