Active control of a rod-net formwork system prototype

Liew A., Stürz Y. R., Guillaume S., Van Mele T., Smith R. S. and Block P.
Automation in Construction
2018
doi: 10.1016/j.autcon.2018.09.002

A prototype rod-net for a fabric formwork system is described, including the fabrication, control of the geometry via turnbuckles, and the measurement of nodal co-ordinates via an image-based theodolite system. Such a net and fabric formwork system consists of a network of tie elements, either discrete or continuous, forming the main falsework structure, onto which is placed a fabric membrane acting as the flexible formwork for the pouring of wet concrete for the forming of a concrete shell. The fabrication of the plastic and steel net components of the prototype is described in detail, including the arrangement of the nodes, rods and boundary conditions. A control system was developed to determine the necessary adjustments at the boundary elements to move the net to a target geometry to eliminate deviations that may arise from fabrication and construction tolerances. This control system showed that with minimal adjustments the net could be directed effectively, resulting in deviations from the target surface reduced from up to 3-9 mm to below 1–2 mm for a 3D net of approximate dimension 2.5 m by 4.5 m by 2.0 m. Additionally, the algorithm provided a more symmetric distribution of deviations around the target. The control system was coupled with 3D point-cloud measurements of markers placed on and around the net system by using a motorised image-assisted theodolite and specialised software for spherical and circular targets. This semi-automated process proved to be both efficient and accurate for determining the spatial co-ordinates of the markers and hence the node locations.