
The Airshell Prototype
This paper by Alessandro Liuti, Sofia Colabella, and Alberto Pugnale, presents the construction of Airshell, a small timber gridshell prototype erected by employing a pneumatic formwork.
Computational analysis of hygromorphic self-shaping wood gridshell structures
Bi-layered composites capable of self-shaping are of increasing relevance to science and engineering. They can be made out of anisotropic materials that are responsive to changes in a state variable, e.g. wood, which swells and shrinks by changes in moisture. When extensive bending is desired, such bilayers are usually designed as cross-ply structures.
However, the nature of cross-ply laminates tends to prevent changes of the Gaussian curvature so that a plate-like geometry of the composite will be partly restricted from shaping. Therefore, an effective approach for maximizing bending is to keep the composite in a narrow strip configuration so that Gaussian curvature can remain constant during shaping.
This represents a fundamental limitation for many applications where self-shaped doublecurved structures could be beneficial, e.g. in timber architecture. In this study, we propose to achieve double-curvature by gridshell configurations of narrow self-shaping wood bilayer strips.
Using numerical mechanical simulations, we investigate a parametric phase-space of shaping. Our results show that double curvature can be achieved and that the change in Gaussian curvature is dependent on the system’s geometry. Furthermore, we discuss a novel architectural application potential in the form of self-erecting timber gridshells.
In this study, we show a way to overcome the mentioned limitations by self-shaping gridshell systems (see electronic supplementary material, movie S1), focusing on orthogonal and interconnected narrow wood bilayer strips. Each wood bilayer strip will strive towards shaping to its natural curvature when the humidity is changed, and ideally, the gridshell system will realize a shape where ΔK > 0.
However, the system’s behaviour, especially the exerted effect of rigid interconnections on the shaping, is yet unknown. In this context, we analyse the self-shaping behaviour of wood gridshell structures at medium scale by parametric numerical studies using the finite-element (FE) method.
By investigating principal curvatures, natural curvatures, mean and Gaussian curvatures, we quantify and discuss the phase-space-dependent shaping behaviour and draw relevant conclusions for application to selfassembly architecture and construction processes. For such applications, gridshell systems offer a lightweight and material efficient method of covering large spaces with structurally performative curved forms.
Our results show that self-shaping wood gridshells enable positive changes in Gaussian curvature (K), which is impossible for solid plate geometries of single bilayer-composites of anisotropic materials.
The shaping behaviour appears to be dictated by complex interactions between the strip’s thickness and width. On the one hand, for thin and narrow strips, the large change in K is enabled by the inplane bending deformations of the strips of the rigid-jointed grid. On the other hand, for thicker and wider strips with lower changes in K, in-plane bending moments enforce the system’s shaping towards values close to or slightly surpassing the natural curvature of single strips.
The presented self-shaping would overcome many of the constraints of post-formed timber gridshells in the sense that complex lifting and forming is replaced with distributed autonomous actuation. Less structure is needed to constrain the shell after forming, tighter radii of curvature, and more complex lamella interactions would be made possible.
This paper by Alessandro Liuti, Sofia Colabella, and Alberto Pugnale, presents the construction of Airshell, a small timber gridshell prototype erected by employing a pneumatic formwork.
In this paper by Gregory Charles Quinn, Chris J K Williams, and Christoph Gengnagel, a detailed comparison is carried out between established as well as novel erection methods for strained grid shells by means of FE simulations and a 3D-scanned scaled physical model in order to evaluate key performance criteria such as bending stresses during erection and the distance between shell nodes and their spatial target geometry.
In this paper by Frederic Tayeb, Olivier Baverel, Jean-François Caron, Lionel du Peloux, ductility aspects of a light-weight composite gridshell are developed.
In this paper by Julian Lienhard, Holger Alpermann, Christoph Gengnagel and Jan Knippers structures that actively use bending as a self forming process are reviewed.
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