Full-scale prototype of a cable-net and fabric formed concrete thin-shell roof

Figure 1: The HiLo roof prototype. This paper describes the construction of a thin shell concrete roof with a novel cable-net and fabric formwork system [1]. The construction of the shell was a proof-of-concept demonstration of the formwork system, showing that through appropriate cable-net component design, and an on-site shape control system [2], concrete shells with complex doubly curved geometry can be built efficiently and with minimal material waste.

The formwork system works by installing a fabric shuttering on a cable-net structure tensioned from stiff boundary beams that are supported by standard scaffolding props. Starting from the lower support points, the concrete shell is sprayed on the flexible formwork from two aerial platforms in a carefully planned sequence. The cable-net is designed to deflect into the designed shape of the shell structure under the weight of the wet concrete. The cable-net nodes are specifically designed to hold the fabric shuttering and to fix the carbon fibre reinforcement at the correct depth in the concrete section. They also serve as an indicator for the variable thickness of the concrete during spraying.

Due to construction tolerances and imperfections, the as-built shape of the cable-net is expected to deviate from the designed geometry. To minimise this deviation, an active control system is used. To reshape the cable-net, the cables on the boundary are tightened or loosened. Based on the measured geometry of the cable-net, a specifically designed control algorithm is used to find the set of adjustments necessary to achieve the desired shape.