Calibrated Modeling of Knitted Fabric as a Means of Simulating Textile Hybrid Structures

Knitted fabrics have unique characteristics compared to conventional architectural membranes. Conventional architectural membranes are composite materials consisting of woven or non-woven textiles and layers of coating. Characteristics of membrane behaviour are a high tensile strength, no bending resistance and a certain shear stiffness. Their resistance against environmental impact is derived from a form found shape with double curvature and prestress keeping the system under tension in all conditions. When combined to a hybrid system with an actively bent GFRP rod, the membrane stabilizes the rod, as the rod tensions the membrane. The doubly curved surface is usually subdivided into developable pieces and sewn together. Knitted fabrics are very flexible and have a high elasticity allowing for complex shapes and double curvature without the need of cutting them in special patterns. CNC-driven knitting-processes allow for integration of channels, pockets and structural details, potentially reducing the effort in further processing. The authors propose a method of simulating knitted fabric as a structural membrane by representing it as a 2-dimensional grid. The grid is calibrated by adjusting its geometry and the stiffness of its members to match the properties of a tested knitted membrane specimen. The advantage of this method is that it is integrated into the design environment of Rinoceros3D and Grasshopper so it can give instant feedback and allow the designer to take informed design decisions. The method is demonstrated on a case study consisting of an elastically bent GFRP arch that is restrained by a membrane on one side. (C) 2016 The Authors. Published by Elsevier Ltd.