Copious amounts of willow, transported by RAV and elevator from afar, arrive at the 13 Floor on Friday 13th and await their tied and twisted fate… experimentation in sculpted surfaces of the coppiced form.
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A 36-square chequer test panel frame, approximately 2.5m square, constructed of willow and adhesive fibreglass mesh tape |
Earlier the same day we had discussed the possibility of gridshell type structures using willow. The small crude test panel I had constructed a few days earlier showed some promise but quickly disintegrated once we had warped and twisted it a few times to examine potential forms.
We wanted to see how much a larger willow framed panel could be deformed without affecting its structural integrity. Now that we had acquired a larger quantity of good quality willow Fran, Qian and I were able to construct a large chequer pattern willow panel in less than an hour.
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| Detail of willow-on-willow joint using tightly wrapped adhesive fibreglass mesh tape |
Though we had previously tested several joint-making materials (including string, tape and thin lengths of willow) we decided to use adhesive fibreglass tape for this exercise; our brief for this project allows the use of non-cultivatable materials for fixing purposes.
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| Panel Warping Experiments – no breakages and joints all held |
We tested the completed willow panel by warping and bending it in several directions. There was no significant impact on any of the joints and apparently no significant stress on any of the individual willow members. However, if we are going to consider a true gridshell type structure then we would need to add additional layers of panels to the first. We would also need to look at how the individual panels would be joined to each other using a method that would allow for easy adjustment and tightening once the required shape had been achieved. We will also look at alternative methods by which to keep the gridshell under tension.
The fibreglass matrix tape doesn’t slip and provides sufficient flexibility while maintaining joint integrity, even through quite severe bends and warps of the panel. There was a small amount of unfurling at the ends of the tape after severe test warps of the panel but this should be fixable by application of a small amount of sprayed PVA (which would impregnate the mesh and increase cohesiveness) or the tie of an additional willow wrap as demonstrated in earlier experiments. Willow ties may well work for the whole structure but fibreglass tape also saves considerable time in assembly, and we are quite constrained time wise!
The key tasks for Monday/Tuesday of the coming week are to look at what materials can be used for infill of such a large panel; additional tests related to shape, form and structural integrity; and planning for the final design.
