Research illuminates the possibilities for creating textile second building skins that can be “controlled” by the environment and user preferences.
By Elena Vlasceanu
Structures are designed and built to offer people protection and comfort. New research seeks to change views concerning how people may interact with buildings and buildings with their environment—not if, but how.
This research demonstrates how textiles can react to environmental stimuli, or respond to human “requests” for a fabric façade to behave a certain way, to elicit a certain behavior in order to provide the kind of environment or protection desired.
An imaginable product resulting from the further development of this work might be a communication platform implementable to a variety of façade or roof systems. The application would register all outlooks of which the geometry is capable, sense user movements and environmental data, and optimize and simplify the relationships among all these factors. It would then directly communicate with the building management system and dictate the deformation of the façade elements. The communication platform could be installed on users’ smartphones or on screens mounted in the building.
The designed façade or roof does not necessarily have to be highly intricate or geometrically and technologically complex to do this, but it has to allow diversity, movement, adaption and “dialogue” with the environment.
Boundary conditions and building typologies
The vast number of possible project geometries compelled the definition of conventional restrictions. Accordingly, the building typologies that might benefit from a multifunctional adaptive second skin were identified. The retracted upper stories, interior courtyard and retracted lower stories cross-section typologies seem to be the main boundary conditions for implementing the desired system. Furthermore, strip-like configurations were investigated, applicable to two stories of the building frame, as this option would be most feasible for the observed construction typologies listed above. The first building cross section was selected as the boundary conditions sample on which all façade outlooks and results were visualized.
Figure 3: Building frame cross section
Specifically because the need for a system that should indeterminately respond to a multitude of impulses and parameters was identified, it was clear that the actual façade elements would have to be geometrically simple, capable of being altered into various outlooks with as little energy as possible. The materials would have to work interactively and ensure kinetic amplification. An analytical method was therefore employed. The represented frame was used to exemplify various actuation/movement possibilities.
The sample configuration has vertical, horizontal and diagonal elements with semi-rigid joints. For some of the actuation options, a few of these elements were removed; a total of 10 different configuration variations were used for the first model phase.
Figure 5: Façade element
Kinetics and physical models
As a main diagram of the kinetics options, a differentiation was made between reactions, or effects of the movement, and actuation, or cause of movement. Actuation can be external or internal: external actuation could be separated into translation and rotation and internal actuation can be divided in contract, expand and bend. As previously formulated, the utilized systematic method dictated applying each kinetics option listed above to each of the 10 configuration variations built and searching for the combination with the largest number of outlooks possible, created with the help of the simplest and most energy efficient actuators.
The type of membrane used also differs from the point of view of its elongation tolerance, some being built of plain weave glass fiber mesh, other of elastic textile material. The models are built on a 1:10 scale; the actuation is schematically simulated by either introducing elastic elements that pull joints together, or rigid ones that push farther apart.
Figure 6, 1-4: Examples of actuation types, physical models 1:10
The physical models were built with the goal of showing diversity allowed by a system, not through the multiplicity of the actuator types or their complexity, but through its intrinsic behavior (determined by the interaction between membrane, outline structure, bending-active elements and the proportions of the stripes). The “contraction” option proved to be the actuation type with the most notable effects on the geometry and that required the most energy efficient movement mechanism (a tension and release system). The built configurations were subjected to contraction of horizontal elements, vertical ones and diagonal components.
Figure 7, 1-4: Diagonal contractions applied in layered phases
Because of their low degree of actuator complexity, combined with a diverse collection of deformed geometry outlooks, diagonal contractions, applied in layered phases to configurations with pre-stressed membrane were investigated further, first digitally and then with the help of mock-ups. The material used for the 1:5 scale models was ATEX Screen semi-transparent, silicone-coated, noncombustible glass fabric.
The conclusions drawn from the physical models phase guided the modeling of the digital simulations and identified the parameters that influenced the creation of the final shapes: the stiffness of the structural elements was one of the main factors responsible for the degree of shape adaption. The membrane pre-stress factors, as well as the way it is fixed to the structure, are equally important parameters.
Figure 8: A representation
The basic geometry of the stripes was built in Rhino3D®. The variations of diagonal, horizontal and vertical elements within the stripes were created with the help of Grasshopper®. The actuation applied on each of the configurations and the membrane layer was simulated with Kangaroo Physics.
Figure 9: Comparison: digital and physical models 1:5
Figure 10: Interglas ATEX Screen
Since 1:5 mock-ups helped prove the validity of the digital models, and all possible digital contractions actuations were simulated with Kangaroo Physics, a library of all 25 possible deformed geometries was created, originating from the same frame configuration and resulting after the activation of the same basic actuator type, a step motor pulling the contracted points closer together. The geometry outlook options in the library represent the possible states of one façade element; the whole building envelope consisting of at least seven stripes is able to take multiple shapes.
The behavior simulation algorithm was programmed in Rhinoscript, with additional Grasshopper and C# definitions. The information exchange between the main algorithm and Ecotect® (used to evaluate the weather conditions effects on the geometry) was also automatic.
Weather information was critical for the façade development process. All geometries in the created library were evaluated for the current weather conditions. These are fed into the algorithm as criteria after being extracted, with the help of Grasshopper (an algorithm editor for Rhino 3D), Geco (a set of components that connects Rhino/Grasshopper and Autodesk Ecotect), and Ecotect (a program that performs simulation and building energy analysis), from a weather file that provides information such as wind speed, wind direction, solar irradiation, humidity levels and temperature.
According to the individual values and position in a predefined order of relevance, each weather criterion is assigned an importance factor. Each geometry is evaluated for each weather criterion, and the separate results are factored by the respective criterion’s weight in order to get the final grade for each geometry, for the current weather conditions.
For example, in order to determine if there is snow, to check if the textile envelope might be in danger of overloading, the humidity and temperature factors are considered simultaneously. Similarly, the algorithm can detect rain and provide shelter on the terrace. The final result of the weather evaluation is a hierarchic list of all geometries, from the fittest one to the outlook that would behave worst under the current meteorological conditions. An initial façade is created, one composed of stripes that find themselves actuated in the form of the fittest geometry.
Figure 11: Possible façade result
The user has the ability at all times to interact with the façade and select a desired effect: light or shadow and size of the desired effect: local/entire room/multiple rooms. If the desired effect is light, then the geometry that leaves the least shadow on this surface projection is searched, and if the effect is shadow the geometry that leaves the largest shadow on the surface is to be found.
The order in which the geometries are considered is the one defined by the current weather evaluation, therefore the end result is a façade made up of stripes deformed to states that best behave in the current conditions and at the same time respect the user’s choice of façade effects. If the weather conditions are not critical, such as storm conditions, the user’s influence can become more relevant for the final outlook if they so wish. Inversely, if the user does not express strong specific wishes, the façade will take the most energy efficient shape.
Figure 12: Façade results for the same conditions, different user position
There are a vast number of possibilities that an apparently basic building envelope offers if its transformation is specific to the employed materials. The kinetic amplification is possible due to the collaboration of the membrane material and the fiber-reinforced composite bending-active elements, connected with semi-rigid joints.
The algorithm and conceptual method created are innovative in terms of extending the limits of the user-façade interaction. One does not overpower the other; the surrounding environment and the user’s influence are at all times simultaneously relevant in a dynamically changing balance.
Figure 13: Visualization
This article is a further development of the work “Responsive Textiles,” conducted by Elena Vlasceanu as a diploma project at the Institute of Building Structures and Structural Design, University of Stuttgart, Germany, under the supervision, and with the collaboration of, Dipl.-Ing. Julian Lienhard and Prof. Dr.-Ing. Jan Knippers.
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