Flectofold—a biomimetic compliant shading device for complex free form facades

Abstract

Smart and adaptive outer façade shading systems are of high interest in modern architecture. For long lasting and reliable systems, the abandonment of hinges which often fail due to mechanical wear during repetitive use is of particular importance. Drawing inspiration from the hinge-less motion of the underwater snap-trap of the carnivorous waterwheel plant (Aldrovanda vesiculosa), the compliant façade shading device Flectofold was developed. Based on computational simulations of the biological role-model's elastic and reversible motion, the actuation principle of the plant can be identified. The enclosed geometric motion principle is abstracted into a simplified curved-line folding geometry with distinct flexible hinge-zones. The kinematic behaviour is translated into a quantitative kinetic model, using finite element simulation which allows the detailed analyses of the influence of geometric parameters such as curved-fold line radius and various pneumatically driven actuation principles on the motion behaviour, stress concentrations within the hinge-zones, and actuation forces. The information regarding geometric relations and material gradients gained from those computational models are then used to develop novel material combinations for glass fibre reinforced plastics which enabled the fabrication of physical prototypes of the compliant façade shading device Flectofold.

Bark, the neglected tree postural motor system

“…Only in the last decade has it been realized that ‘clever’ bio‐inspired arrangements of reinforcing fibers or fiber bundles could be used for building biomimetic fiber‐reinforced motile structures, as exemplified in the façade‐shading systems flectofin ® and flectofold (cf. Schleicher et al ., ; Körner et al ., ). Another example, perhaps even closer to the mechanism described by Clair et al ., is the fluidic muscle, where a network of fibers embedded in a polymer cylinder causes a considerable shortening when the cylinder is hydraulically or pneumatically pressurized.…”

Effect of Gravity on the Scale of Compliant Shells

“…This In accordance with Equation (8), the gravitational force is larger (in magnitude) as the scale of the shell increases. This is appears in Figure 4 with thin shell of larger characteristic dimensions having low values of G i such as for example façade shading shells [16,17,28]. Shells with a characteristic dimension R lower than 0.1 m tend to have Gi > 1.…”

“…While biologically compliant shells appear at the smallest of the 10 length scales cited above, the use of those structures in biology has started to inform the design of engineered mechanisms at larger scales. Examples of flexible shells observed in nature have inspired engineered scale adaptive structures [15][16][17][18] at the meter scale, but the question of whether such structures could be scaled up even further still remains open and drives this study. This succinct literature review shows that there is a clear gap of knowledge as to what the limiting scale of compliant shells is and what the defining parameter is that determines this scale.The main hypothesis guiding this study is that the lack of large-scale compliant shells is due to the limiting effect of gravity-induced body forces on the shell's movements.…”

Additive manufacturing of cellulose-based materials with continuous, multidirectional stiffness gradients

“…Second, for the development of materials, the range of material stiffness can be further extended, and alternative viscous materials could be used, such as other polymer gels, resins, or even materials used in large-scale industries, assuming an appropriate hardware setup is introduced. Third, the main concept of this work could be extended to current large-scale printing technologies (38,39) to create buildings in which geometry and material continuously change to balance between structural and architectural requirements or even to create adaptable mechanisms (22) to introduce soft hinges or directional bending. Fourth, at the other end of the size spectrum, it would be interesting to test the effectiveness of the established method at small scales, where the natural diffusion of the material may overtake the distribution specified by the fabrication paths, which would be crucial for applications sensitive to small changes in material properties, such as tissue engineering.…”