Hybridating vertex and face normals to design torsion-free gridshells: application to the X-Mesh pavilion

The fabrication of a freeform structural envelope is usually a highly complex task. The costliest aspect is often the connections between the constitutive parts. X-Mesh is a pavilion that demonstrates a new rationalization strategy. Its structure, composed of a hexagonal grid of beams and cladding panels, is based on a geometry that rationalizes connections at two levels: firstly, nodes are repetitive, only two types of nodes are used. Secondly, panels can easily be connected to the support beams as they are orthogonal to each other. We prove that the proposed geometrical configuration can be asymptotically built on a smooth surface. We generate the meshes by numerical optimization from a smooth target surface, with an initialization derived from the asymptotic case. This pavilion shows another way of rationalizing a gridshell beyond the popular planar-quad meshes and circular/conical meshes. It also demonstrates a way to generate hexagonal gridshells which are not necessarily synclastic, this limitation being typically imposed to achieve planarity of cladding panels.