Single Cast Fabric Formwork
December 3, 2010
Concept of a single cast structure:
It is inevitable that architectural components require connections. However, the position of the connections is required to be in the best interest of the structural element, form, construction and aesthetics. One of the other reasons for pre-fabricating and casting separate pieces to fit together is for transportation, but of course concrete can be poured in situ! This posed a question about what was possible to achieve through the process of stitching – essentially tailoring fabric to generate a form.
We admired the past work done of the previous years, but were critical of the techniques used to connect fabric formed elements and argued that quite a few of the connections were infact unecessary. The qualities of fabric formed concrete is to use its inherent properties of the fabric to manipulate the plasticity of concrete.
Our position asked the question about what a beam and column could become. A beam needn’t be joined to a column as two individual pieces, could they be cast as a single element using sewing to stitch and shape the formwork using sleeves? We thought a more rational form might result if each element was cast together as a single entity using the qualities of the fabric to dicate the form. Our joint was made in the formwork itself.
Additionally, such a concept opens up new tangents and industrial possibilities in concrete construction methods. Suddenly a piece of fabric formwork can be specified (using the guiding principles), stitched in a textile factory off site, transported easily in a bag to a site, unfolded, hung into position with the use of simple scaffolding and minimal timber structure and cast on site as a single entity. Our aim was to prove this concept with a large free standing singularly cast enclosure: a wall with two columns.
The video of the frame and formwork construction, the pour and the final peel can be seen at the link below.
Our prototype structure was successful with only a couple of complications due to not quite getting one of the columns verticle when we cut the holes – something that could be easily corrected by using a pole as a guide. As a result, the fabric at the sleeve wasn’t tense enough and risked a lack of concrete in the joint. Our solution was the tie the column back to the frame, to straighten it up and put the fabric into tension again. The result is a jaunty slender column that is quite appealing and has the remains of the rope marks on the surface as another reminder of process.
There is an even surface finish with very few imperfections over the whole surface. One area of imperfection however is towards the base of the wall that has not compacted fully because we were distracted by two burst cotton stitches, positioned to control the mass. The bottom most stitch survived, which proves the concept that it a simple 1cm square stitch can be used to control the mass and prevent it bulging. In the case of the other two, we determined that we weakened the fabric around the thread by over sewing it – making the stitch stronger than the cotton itself, resulting in a tare under the pressure of the concrete. We patched the breaches quickly, but the ‘bullet holes’ remain as evidence on the surface. However, it is interesting to see the difference in mass compared to the successful stitch at the base of the wall.
Another slight area of improvement is in the footings, where we were unable to access the concrete during the pour and probably didn’t vibrate the base enough to get a full compaction. The result is that some of the aggregate around the edge comes away and the concrete is imperfect around the base, but it is not in any structural danger.
It is fascinating to walk around the structure and look through the structure at different angles to appreciate the slenderness and the geometry. A space is defined by the structure, that gives an architectural language determined by the positioning of material.
In the context of our unit’s title Distructive Technology: Material Immaterial – the discussion that formed a critical part of our design process, that now only exists as notes and sketches, represents an immaterial property of a material concrete structure. In the process we have developed a language, a code, to work with this material and discuss its process and potential wtih other people. We have developed an understanding between material and immaterial.