Climate Adaptive Building Solutions Based on the Autonomous Movement of Wooden bi-layered Structures

The global warming due to green-house effects and their negative consequences, calls for new renewable and sustainable engineering building solutions. Climate Adaptive Building Shells (CABS) are currently object of many researches, because of their energy saving potential based on autonomous responsiveness to changing climate conditions. However, the most part of CABS systems currently available on the market are driven and controlled by energy consuming sensors and actuators. The current thesis deals with material selection and geometrical strategies to upscale wooden bilayers for their implementation in adaptive building façade systems. The wooden bilayers used in the current work, are made by two wood layers. One layer the so-called active layer, which has high shrinkage and swelling properties, and one layer, the so-called passive layer with less dimensional changes. The layers are bonded with an orthogonal fiber orientation at high relative humidity. Upon a decrease in relative humidity the bilayers turn from a flat to a bent configuration. In the first part of the thesis, wooden bilayer actuators, which had been previously manufactured at the small (strips) scale, were upscaled. The response time and the kinetics of the upscaled bilayer have been improved and optimized, based on a comprehensive parameter study. Annual growth ring orientation, ratio of the two layers thickness as well as an overall bilayers thickness suitable for engineering applications have been optimized in order to achieve a unidirectional or so-called monoclastic curvature. When upscaling to up to half-meter length, the response time of the bilayer goes up, since a substantial moisture gradient occurs in the active layer. Therefore, design principles for increasing the rate of MC loss/gain and thus rate of curvature change have been introduced and studied. These geometric strategies comprise milling of horizontal or diagonal grooves into the active layer in order to reduce the water diffusion path length. The kinetic of the milled and non-milled bilayers have been tested for multiple de/adsorption cycles in order to prove their repeatability and reversibility. Besides the optimization of the geometric design of the bilayers, the effect of different bonding types on the bilayers response time and curvature was analyzed. During the bilayers bending the properties of the adhesive could play an important role not only for the water diffusion but also for the mechanics of the layers connection. Particularly, the layers connection is important for achieving a homogeneous and continuous curvature of the bilayers. Different adhesives, which can be grouped in water introducing and non-water introducing have been tested. MUF (Melamine Urea Formaldehyde), PRF (Phenol Resorcinol) and PVAC (Polyvinyl Acetate) were chosen for the water introducing group while PUR (Polyurethane) and Epoxy adhesive from the non-water introducing group. The kinetic of the bilayers was tested also in this case for multiple de/adsorption cycles. The amplitude of the response time of the bilayers as well as the amplitude of the bilayers bending was not affected by the different adhesives used. However the use of water introducing adhesive led to an initial MC of the bilayers, which was around 1-2% higher than for bilayers bonded with non-water introducing adhesives. Despite the optimization of several parameters relevant for the kinetics of the bilayers, it became obvious that a single upscaled bilayer curves too slowly to be implemented in a CABS applications. Therefore, the coupling of two wooden bilayers through a lever arm configuration was introduced. Coupled bilayers are composed of an active bilayer, permanently restrained, which bending is responsible for the rotation of a passive bilayer. Five different coupled configurations have been characterized at the strip-scale. Next to the response time, the kinetics of the coupled systems were studied in terms of angular change and rate of angular change of both bilayer elements. The achieved amplification through the lever arm approach shows an optimization of the overall system response time compared to the kinetic of a single bilayer. No differences in the kinetics were found between the five coupled typologies. Out of this five, one typologies was upscaled and a potential implementation in a shading system was discussed. This typology was chosen for the upscaling, because of an inherent protection of the active bilayer against weathering, which is crucial for several engineering applications. In the final part of the thesis a study in collaboration with the Institute for Computational Design and Construction (ICD) at the University of Stuttgart is presented. In this study, two different wooden bilayer types were investigated. On the one hand bilayers made by two wood layers, on the other hand hybrid bilayers made by wood and glass fibers. Regarding the wood bilayers, complex bilayer bending was analyzed. Besides the monoclastic curvature aimed at and presented in the major part of this thesis, a double curvature or so-called anticlastic curvature was intended, achieved and characterized not only at the strip scale but also in the upscaled configuration. The upscaling of the wooden bilayers has been done not only in terms of the plate dimensions, but also for the overall bilayer thickness. In fact, the upscaling in thickness is important to design bilayers for outdoor applications with a sufficient robustness. Wood and wood hybrid bilayers can be combined by using finger joints to overcome the inhomogeneity of the wood and to allow for the development of self-forming structures at the macro-scale based on a water responsive material