Designing Architectural Morphing Skins with Elastic Modular Systems

This paper discusses the issues of designing architectural skins that can be physically morphed to adapt to changing needs.To achieve this architectural vision, designers have focused on developing mechanical joints, components, and systems for actuation and kinetic transformation. However, the unexplored approach of using lightweight elastic form-changing materials provides an opportunity for designing responsive architectural skins and skeletons with fewer mechanical operations. This research aims to develop elastic modular systems that can be applied as a second skin or brise-soleil to existing buildings.The use of the second skin has the potential to allow existing buildings to perform better in various climatic conditions and to provide a visually compelling skin.This approach is evaluated through three design experiments with prototypes, namely Tent, Curtain and Blind, to serve two fundamental purposes: Comfort and Communication.These experimental prototypes explore the use of digital and physical computation embedded in form-changing materials to design architectural morphing skins that manipulate sunlight and act as responsive shading devices. 1. RESPONSIVE KINETIC SKINS The term “Responsive architecture” was coined by Nicholas Negroponte in the mid seventies when spatial design problems were beginning to be explored through digital technologies [1]. In recent examples, responsive and kinetic architectural design can primarily be found in building envelopes or skins.These approaches to designing architectural skins comprise the adoption of kinetic mechanisms for environmental adaptation and responsiveness.The term “Kinetic architecture” was introduced by William Zuk and Roger H. Clark in the early seventies when dynamic spatial design problems were explored in mechanical systems [2].This concept differs from responsive architecture since it investigates a building’s capacity of motion with less consideration of response to environmental conditions. Kinetic architecture often focuses on expensive and complicated kinetic and mechanical systems as well as physical control mechanisms for actuation and structural transformations.The responsive kinetic skin of L’Institut du Monde Arabe at Paris designed by French architect Jean Nouvel in 1987 is a significant precedent which is known for its mechanical failure.A decade ago, dECOi attempted to integrate responsiveness and kinetic skins to create and investigate responsive architectural facades and installations, such as the Aegis Hyposurface [3], by using high-tech mechanical solutions, such as multiple piston components to actuate transformation [4]. However, solutions involving such mechanical components require designers to deal with the high energy cost and complex mechanisms. In the Aegis Hyposurface, piston components were found to be prone to fatigue-failure, causing gaskets leakage from the piston [4]. Such a ‘hard’ mechanical approach often produces brittle and vulnerable kinetic systems.Thus, reliability and longevity factors of the system are the main challenges for kinetic architectural skins to become a more widely adopted approach in architectural design. How to design kinetic architectural skins with fewer mechanical operations? New ‘soft’ architectural components like elastic silicone polymer and other active form-changing materials offer new possibilities for designing kinetic, responsive skins. In this paper, we describe a ‘soft’ approach, which integrates digital and physical computation with elastic materials to embed responsive and kinetic morphing abilities into architectural skins.This ‘soft’ approach has the potential to address the brittleness of the hard mechanical components. Although ‘soft’ architecture is a concept introduced during 60s and 70s, there is still limited progress in this domain [5]. In order to pursue this vision, further exploration with kinetic materiality is needed.This research explores the use of ‘soft’ elastic form-changing materials for constructing kinetic and responsive architectural models.The purpose of this investigation is to address performance and aesthetics demands in designing soft responsive architectural skins.We propose that a more organic approach with less mechanical operations can harness material properties 399 Designing Architectural Morphing Skins with Elastic Modular Systems to produce transformations on architectural morphing skins. Omar Khan’s Gravity Screens provides a novel active response where surface form results from gravity’s effect on the elastic material patterning.These elastic mutable screens provide possibilities for responsive space that can mutate from circulation corridors to room clusters [6]. However, Khan’s work just provides a starting platform for the soft responsive architectural idea and there is still unexplored territory to expand from the ‘hard’ to the ‘soft’ approach. Current researchers attempting to address this ‘soft’ approach include Tristan d’Estrée Sterk and Kas Oosterhuis with the use of pneumatic muscles in their projects. Sterk designed a responsive architectural structure by applying tensegrity (or tensional integrity) components actuated by pneumatic muscles [7]. Oosterhuis used pneumatic muscle as an architectural membrane to respond to various spatial conditions [8].The members in a tensegrity structure are segregated into those which carry only compressive and those which carry only tensile forces in a way that obviates the need for direct contact between adjacent compressive members, giving them the appearance of floating in space.The recently completed Media-ICT building designed by Cloud 9 Architects in Barcelona is an example of a highly energy efficient building, achieved through the implementation of the ‘soft’ approach to kinetic architectural skins.The complex façade made of ETFE (Ethylene Tetrafluoroethylen) protects the interior by moderating direct sunlight in a way that is responsive to changing conditions [9].The project ShapeShift is taking another approach using kinetic membranes with EAPs (electro active polymers) and “parametric paravent”, prototypes of robotically fabricated room-dividers [10]. Beyond the described examples, work that investigates the porosity and permeability of ‘soft’ architectural envelopes that respond to environmental and communication inputs is largely unknown at this stage. In this study, we are using passive and active design strategies to create kinetic prototypes that minimise the need for complex mechanical actuations as the basis of soft kinetic systems.All the experimental models that have been prototyped in smaller scale through this study combine material explorations, digital and physical computing techniques, as discussed in section 3.The main idea behind deploying soft kinetic systems for designing morphing skins is the integration of an exoskeleton structure, and a surface as the actual actuator. Hence, soft kinetic systems do not require mechanical joints, parts, or motors.The kinetic actuation also takes place in the overall modular system with the use of form-changing materials and little use of mechanical components.This concept is inspired by the soft mechanical approaches in aerospace engineering especially morphing wing technology [11]. In the field of engineering, the word morphing is used when referring to continuous shape change i.e. no discrete parts are moved relative to each other but one entity deforms upon actuation [12]. For 400 Chin Koi Khoo, Flora Salim and Jane Burry example, on an aircraft wing this could mean that a hinged flap would be replaced by a structure that could transform its surface area and camber without opening gaps in and between itself and the main wing [13].This fascinating concept of morphing skin as an emerging aerospace technology has inspired aircraft wing design but it has remained unexplored territory in terms of architectural morphing skins. The study presented in this paper aims to develop prototypes of architectural morphing skins, since the elastic nature of these structures is able to accommodate responsive mechanisms with passive elastic memory while minimising the energy and weight required for actuation.Although the research encompasses consideration of energy use and the cost of maintenance, these are not part of the scope of this paper.We argue, as an early hypothesis, that elastic modular systems can provide designers with a mix of passive and active design strategies to manipulate architectural morphing skins.We test this argument through design experiments with small-scale models.The paper describes and discusses the development of a new repertoire of responsive architectural morphing skin ideas using accessible ‘soft’ components, such as elastic materials integrated with contemporary sensor devices.These ideas are developed using parametric design tools. 2. PROPOSAL: ELASTIC MODULAR SYSTEMS Modular systems are not uncommon in architectural design.Their use has largely been concerned with reducing cost and the materials needed to construct full-scale architecture. In contrast to existing kinetic systems, for instance, the Aegis Hyposurface and L’Institut du Monde Arabe projects, Elastic Modular System (EMS) offers movement and change in response to material properties rather than changes in mechanical components such as actuated motors and gears based on the concept of soft kinetic systems as discussed in section 1.This shift challenges the notion of kinetic structure relying on external actuation.This approach, although similar to soft mechanical approaches in aerospace engineering such as the morphing wing design, has not liberated the transformable skin from the requirements of a sturdy structure [14]. Modular components of the skin act as a lightweight structural support and a spatial envelope at the same time. The purpose of the development process presented in this section is to design architectural morphing skins using the soft approach in a simple yet efficient way.The design process requires iterations of physical and digital modelling, electronic prototyping and fabrication.Through each stage of the development process, Skeleton, Skin, Transformation and Adaptability; the data is exchanged between digital and physical models (Figure 1). The four stages for the process of designing EMS as discussed in this paper include: 401 Designing Architectural Morphing Skins with Elastic Modular Systems 1. Skeleton the first stage of the design requires modular components of skeleton to be sketched, modelled, and fabricated. They are represented in the form of parametric digital and physical tensegrity modules (tetrahedra) as part of experimentation process. 2. Skin the second stage investigates accessible elastic and formchanging materials such as silicone rubber, nylon coated stainless steel string and SMAs (shape memory alloys) for physical implementation. 3. Transformation the third stage focuses on the new possibilities of the elastic and form-changing materials to emulate simple transformable mechanisms like joints, actuators and hinges that could become an alternative toolkit to conventional mechanical components. 4. Adaptability the last stage of the system discusses the adaptability of models in order to achieve morphing skins that display elastic properties, able to respond to digital and physical stimuli, and facilitate a feedback loop to the system. The overall design process conforms to a Sensing-Analysis-Actuation (SAA) system diagram that is general to the responsive set-up within the EMS in all three of the design experiments that are discussed in subsections 3.1-3.3. Firstly, the sensors receive the analogue data that is sent to an Arduino microcontroller with Arduino code for processing.Then, the FireFly plug-in embedded in the Grasshopper program reads the processed data and produces the values that activate the form-changing materials for actuation. The contraction and expansion of the actuated form-changing materials produce kinetic movement in the models as they respond to the external stimuli (Figure 2). Figure 1:The process of designing Elastic Modular System (EMS). 402 Chin Koi Khoo, Flora Salim and Jane Burry Virtual parametric models can be associated with real time data from sensors, which stream data from the physical environment, as input to drive the parametric variations in the model [15].The Sensing – AnalysisActuation process is a way of working that has been called form fostering, which enables interoperation and integration of digital, physical modelling and computing through associative design [15]. Form fostering facilitates the parametric model to be the platform for simulating the behaviours of the elastic modular systems in the early design stage. The process of designing EMS requires research to be performed in three distinct but overlapping areas: elasticity, tensegrity, and form-changing materials. Elasticity refers to the ability of a body that has undergone deformation caused by applying force to return to its initial size and shape once the distorting force is removed [16]. Elasticity is a result of the chemical bonds between the atoms that a material is made of [17]. During deformation potential energy is stored within the material which activates the acceleration back to its original state.This offers potential new forms of flexibility, adaptability and deformation using the memory effect in architectural skins. Despite this obvious potential, such material systems have not found widespread application: architects have tended to shy away, cowed by questions of liability and lack of experience [16]. The term tensegrity coined by Buckminster Fuller by combining the words tensional and integrity is a structural principle based on the use of isolated components in compression inside a net of continuous tension, in such way that the compressed members do not touch each other and the pre-stressed tensioned members delineate the system spatially[18].Thus, the tensegrity structural approach reduces the friction between mechanical joints and achieves a lightweight structure which is particularly interesting when considering the development of responsive systems. Due to the interdependent nature of all the compressive elements, a slight change in any of their parameters can result in a significant form transformation [19]. 403 Designing Architectural Morphing Skins with Elastic Modular Systems Figure 2: The generic system diagram of SAA process. For these reasons the tensegrity structure was chosen as part of the EMS and for its flexibility and lightweight components. There are several form-changing materials, such as those shown in Table 1. However, there has been little investigation into the use of these materials as an actuator for structural adaptation and transformation in the architectural context. In this paper, an experiment with form-changing materials will be presented in subsection 3.3. Form-changing materials Commercial Electrical Actuation Transformation (electrical and heat stimuli) stimuli Shape memory alloy Yes Yes Strong Large Shape memory polymer No Yes Weak Large Elastic polymer Yes No N/A Large Piezoelectric crystals Yes No N/A Small Dielectric electro active polymer No Yes Medium Large Ionic electro active polymer No Yes Strong Large Paraffin wax (liquid) No No Strong Large The concept of EMS is explored through implementation in three different prototyped design experiments: Tent, Curtain and Blind. These modular design experiments served as the methods of inquiry.They focus on the research areas: elasticity, tensegrity, and form-changing materials. Each experiment is conceived to achieve individual goals for the overall design process as set out in Table 2. Design Goal Research Implementation experiments areas focus Tent Flexibility with ‘memory’ Elasticity Architectural skin Curtain Transformation Tensegrity Structure Blind Actuation Form-changing materials Actuator These design experiments are conceived as analogue proof of concept for the early architectural morphing skins effects already simulated by computational methods.These early concept models explore active and passive modes of response to changes in the environment.They consider both environmental comfort and use of responsive skins for communication. 3. DESIGNING ARCHITECTURAL MORPHING SKINS This section describes the design process for three design experiments using the Elastic Modular System (EMS).The Sensing-Analysis-Actuation (SAA) process discussed in section 2, is integral to these experiments Elasticity, Tensegrity and Form-changing materials in the context of designing responsive morphing skins. 404 Chin Koi Khoo, Flora Salim and Jane Burry Table 1:The comparison of form-changing materials driven by electrical and heat stimuli. Table 2: Design experiments’ goal, research areas, and implementation focus. The first experiment explores the area of Elasticity by using an assembly of passive tetrahedral elastic modules to represent the morphing architectural skin. It investigates the performance, capacities and behaviour of this system under external actuation.A second and subsequent experiment develops the elastic modules of the first prototype to minimise the number of components and reduce the weight of the module in the assembly of the Tensegrity exoskeleton of the morphing skin.The third and last experiment emulated an implementation of Form-changing materials to become the actuator as well as the skeleton structure of the morphing skin. These exploratory design experiments test the hypothesis discussed at the beginning of this paper that elastic modular systems can provide designers with a mix of passive and active design strategies to manipulate architectural morphing skins. 3.1. Design Experiment 1: Elasticity-Tent Tent is a responsive elastic architectural skin assembled by series of elastic tetrahedral modules. It contracts and expands without mechanical components such as motors or pistons. It is a kinetic tent-like skin which changes shape to meet various needs and environmental conditions. The initial idea of the elastic experiment was to demonstrate the ability of the structure to reconfigure itself to allow physical change to respond and adapt to inputs. However, this idea needs further exploration especially in terms of energy and weight.This section describes how the experiment Tent addresses the issues of energy and weight by using lightweight, simple elastically-transformable modules which respond to stimuli by changing their form. It aims to test on one module: ‘elastic tetrahedron’ the central hypothesis that elastic modular systems can provide designers with mix of passive and active design strategies to manipulate architectural morphing skins (Figure 3). The intention of this experiment was to discover general directions to apply to future ‘soft’ solutions to responsive design and weight issues.The elastic experiment focussed on the new possibilities of elasticity for architectural morphing skins in the following areas: • Elasticity as structureThe structural, architectural components for architectural skins that can expand and contract. Figure 3: Elastic tetrahedron module is formed by elastic string and plastic hollow straws for their lightweight and flexible purpose. 405 Designing Architectural Morphing Skins with Elastic Modular Systems • Elasticity as membraneA ‘soft’ architectural surface will be explored through harnessing elastic polymer properties.This tests aspects of the feasibility of implementing passive amorphous building membranes that respond to external environmental stimuli. • Elasticity as actuationThe novel application of elastic material as an actuator. It excels for its light weight and for the possible substitution for the use of mechanistic joints and pistons.An example is pneumatic balloons or muscles for global actuation, that reduce weight and fiction between parts compared to equivalent mechanical systems. These were the lines of inquiry for the experiment Tent. First, the assembly skeleton components of Tent included using accessible, basic materials such as elastic string as a primary material and hollow straws to fabricate the elastic tetrahedron module used as supportive and expendable structure (Figure 4). Second, the skin of Tent is the inflatable elastic polymer in ‘balloon’ form that serves as actuator and skin simultaneously.The approach created novel effects that mimic ‘organic’ movement and behaviour.The skin itself is elastic and expandable and achieves a high degree of flexibility and adaptability. The third area used the pneumatic actuation through the skin to trigger the general morphological transformation of the Tent. Through expansion and contraction, the combination of individual tetrahedral modules forming the Elastic Space-Frames perform complicated morphing behaviour that can thus be envisaged at full scale (Figure 5). This experiment – the responsive Tent is mimicking a simple living organism that responds to proximity to form the responsive Tent. The initial adaptability test of Tent assessed its response to proximity.This test used pneumatic ‘balloons’ to actuate the flexible contraction and expansion of the surface.A microcontroller controls this process to drive change between various states while force is applied, and return the surface to the original state if the force is released (Figure 6).This set up minimised the energy that would otherwise have been needed for local actuation. It aims to develop a low-technological approach to performance structures that possess adaptive and evolutionary personality related to environmental stimuli using the SAA process discussed in section 2. 406 Chin Koi Khoo, Flora Salim and Jane Burry Figure 4: Initial test of Elastic SpaceFrame as skeleton that perform as contract and expendable skeleton.