Deployable Gridshells as Formwork for Concrete Shells

Concrete shells were used extensively in the 20th century for their efficient use of materials, however the cost of producing the complex form in rigid planar material was often prohibitive and the use of shells declined. This paper examines the potential to use gridshell as a redeployable formwork system for concrete shells. Gridshells have seen a revival in the last decades following the successful design and completion of the Weald and Downland timber gridshell in Sussex, UK and Savill Garden Gridshell in Windsor, UK. Intrinsically linked to architecture and structure, the projects embed, embody and unify construction understanding and forming process, epitomising the holistic trinity of architecture, structure and craft. The gridshell deforms from a 2-dimensional timber lattice flat-mat into into a three-dimensional structure, whose geometry is held at the abutments. Thus complex 3D forms can be produced from a simple 2D planar assembly. The idea of using a flat-mat as concrete formwork was previously presented in Tang 2012 [1]. The work reported here continues from that point to investigates the use of a deployable gridshell as a reusable, recyclable and re-configurable formwork for concrete shell construction. This paper presents, the results of trial construction of two concrete shells using a gridshell coupled with a textile membrane as formwork. A particular point was to demonstrate the redeployment of the gridshell. The same flat mat gridshell was used to construct each shell. The height span and width of each shell varied. Of interest is the initial testing of system feasibility, analysis and subsequent improvements made in constructing concrete shells. Digital image correlation and a careful survey of the deformations were made. These were used to understand that physical response of the deformable formwork during casting.. A detailed study of final geometry of the shells was undertaken and compared with the initial geometry of the gridshell.