# Building in concrete with a knitted stay-in-place formwork: Prototype of a concrete shell bridge

Popescu M., Reiter L., Liew A., Van Mele T., Flatt R.J. and Block P.
Structures
2018
doi: 10.1016/j.istruc.2018.03.001

A novel formwork system is presented as a material saving, labour reducing and cost-effective solution for the casting of bespoke doubly curved concrete geometries. The approach uses a custom knit technical textile as a lightweight stay-in-place formwork with integrated solutions for the insertion of additional elements, and is fabricated as a nearly seamless fabric. Using weft knitting as the textile formation technique minimises the need for cutting patterns, sewing, welding or gluing, when compared to conventional weaving and gives the possibility to integrate channels, openings, have varying widths and directional material properties, thus broadening the geometric design space. The system has been tested through a small-scale concrete footbridge prototype, built using a pre-stressed hybrid knitted textile and a bending-active structure that acted as a waste-free, stay-in-place, self-supporting formwork. Through the gradual buildup of strength in thin layers of concrete, formwork deformations during casting were minimised. This allowed for low tensioning of the fabric and the possibility to use more pressure (e.g. during shotcreting) in applying the subsequent concrete without intermediate support from below. The computational design and fabrication of the knitted textile formwork included integrated channels for the insertion of bending-active rods, tensioning ribbons and features for controlling the concrete casting. The analysis and process of increasing the stiffness of the lightweight and flexible formwork is presented. The hybrid approach results in an ultra-lightweight formwork that is easily transportable and significantly reduces the need for falsework support and scaffolding, which has many advantages on the construction site.

BibTeX

@article{Popescu2018,
author  = "Popescu, M. and Reiter, L. and Liew, A. and Van Mele, T. and Flatt, R.J. and Block, P.",
title   = "Building in concrete with a knitted stay-in-place formwork: Prototype of a concrete shell bridge",
journal = "Structures",
year    = "2018",
volume  = "14",
number  = "",
pages   = "322-332",
month   = "June",
doi     = "10.1016/j.istruc.2018.03.001",
note    = "",
}

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