Precast Barrel vault production from fabric-formed mold.
PRE-CAST VAULTS AND MOLDS
Funicular thin-shell compression vaults (i.e. vaults that are shaped to follow very efficient natural compression geometries) can be constructed by spraying concrete onto hanging sheets of fabric. Like all the work done at CAST, this research uses only simple, flat, fabric sheets cut directly off a standard roll of fabric. In this case these fabric sheets are hung horizontally (like a “hammock”) and then loaded with a thin coating of fibre-reinforced concrete. This causes the fabric membrane to deflect under the load of the wet concrete into the tension resistant shape dictated by its load and support conditions. Because tension and compression are geometric reflections of each other, the resulting funicular tension shape can be flipped over to provide a rigid, fabric-covered, mold for the precast production of thin-shell funicular compression vaults. The fabric sheet can be suspended using any support condition, and any distribution of load as may be required by circumstance or design, and the loaded fabric sheet will automatically form itself into a pure funicular mold for that support and loading condition.
This method was developed through a series of small model constructions using a light plastic membranes and sprayed plaster. The first full scale test of this method (2004) was done at the Lafarge precast factory in Winnipeg, Canada, using a sheet of inexpensive woven polypropylene geotextile hung as a simple barrel vault. A second test (2007) was done using a random fibre-reinforced concrete sprayed onto a coated polypropylene fabric. Future tests will investigate the use of coated fabrics that will permanently attach themselves to the sprayed concrete in order to make a rigid, plastic-coated mold that can be used for pre-cast production of thin-shell structural vaults.
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