Axel Körner

Abstract

This research proposes an additive manufacturing approach for unprocessed concrete rubble on or off-site as a continuous granular system to reduce post-processing and cement binders. A circular knitting machine end-effector, equipped with a camera and time-of-flight sensors, is used to create a seamless, coarse textile container, incrementally filled with rubble and deposited in a layer-by layer sequence in curvilinear, continuous toolpaths, resembling FDM 3D-printing. Material, fabrication, and design experiments present the possibility for self-supporting, compression-only forms such as columns, arches, and walls. Fabrication experiments showcase the feasibility of the system, achieving overhangs up to 25°, arches with a 1:2 span-to-height ratio. Compression tests showed improved load bearing capacity, attributed to the seamless, knitted container. Deformation due to settlement and layer misalignment is the key system limitation. Image segmentation and toolpath height adaptation were used to monitor the jamming and layer height to improve fabrication quality, but this can be expanded. Future work can explore the impact of weathering, bio-based binders for weatherproofing, as well as digital twin technology to enhance fabrication.

Abstract

Angesichts des steigenden Energiebedarfs im Gebäudebetrieb gewinnt die Entwicklung adaptiver Fassadensysteme zunehmend an Bedeutung. Insbesondere solaraktive Gebäudehüllen bieten Potenzial, durch gezielte Steuerung von Sonneneinstrahlung, Belüftung und Tageslichtnutzung den Energieverbrauch zu senken und gleichzeitig den Nutzerkomfort zu erhöhen. Das Forschungsprojekt FlectoLine-Fassade verfolgt das Ziel, intelligente, materialbasierte adaptive Fassadenlösungen ohne klassische Antriebs- und Steuerungssysteme zu realisieren. Im Zentrum stehen dabei flexible Faltelemente, die auf bioinspirierten, nachgiebigen Mechanismen basieren und sich durch die elastische Verformbarkeit von FVK-Platten ohne Gelenke auszeichnen. Durch integrierte pneumatische Aktuatoren, präzise programmierte Materialsysteme und gezielte Differenzierung der Steifigkeiten kann eine kontrollierte Faltbewegung bis 90° erreicht werden. Neben einem Hybridmaterialsystem wurde eine thermoplastische Variante entwickelt, die einfacher zu fertigen und recycelbar ist. Umfangreiche Belastungstests belegen die Langlebigkeit beider Systeme. Ergänzend wurden flexible Photovoltaikzellen integriert, um Energie zu gewinnen. Ein digitaler Zwilling mit Sensorik und Wetterdaten steuert die Fassade in Echtzeit. Der Demonstrator mit 101 individuell verformbaren Elementen auf 83,5 m2 zeigt die technische Umsetzbarkeit und das energetische Potenzial adaptiver Fassadentechnologien der nächsten Generation.

Abstract

Bio-based and waste-sourced materials are emerging as sustainable alternatives to reduce resource extraction and construction waste in the Architecture, Engineering, and Construction (AEC) industry. Unlike conventional materials such as brick, concrete, or steel, they are renewable, locally available, and support circular economy principles. Agricultural fibers like hemp offer high carbon uptake and frequent harvest cycles but exhibit variability due to environmental factors. Similarly, reclaimed materials are influenced by prior use, residual performance, and inconsistent availability. These properties contrast with current manufacturing standards, which prioritize uniform materials suited for standardized fabrication. While data-driven modeling and in-line sensing offer solutions for material variability, existing workflows remain optimized for mass production and lack flexibility to integrate bio-based and reclaimed resources. This paper examines how bio-based and reclaimed materials impact design and fabrication, focusing on the capabilities and limitations of current CAD and CAM workflows. Through architectural case studies, it explores: Capabilities: How well can CAD, CAM, and simulation tools accommodate material variability? Limitations: What barriers hinder large-scale adoption, and at what stages? Opportunities: What workflow modifications can enhance adaptability? The case studies cover timber, agricultural fibers, and biopolymer-based materials, analyzed alongside their fabrication methods—milling, fiber winding/kitting, and 3D printing. Insights from these studies inform the Adaptive Production Chain (APC), a new methodology for integrating material characterization with design and fabrication. APC fosters adaptive, circular workflows, aligning material properties with production processes to promote sustainable innovation in the AEC industry.

Abstract

A continuously adjustable façade shading system functionalized with photovoltaics enables, besides adaptive shading, energy harvesting by solar tracking. This requires large bending motion in two directions. In this paper, the development of an appropriate façade module – FlectoSol – is presented. To achieve motion of ±80°, first time two pneumatic actuators are integrated into a GFRP-elastomer hybrid composite. To improve energy efficiency resp. air pressure consumption of actuation without impairing shading, a parametric study is performed. In detail the influencing criteria of the bending motion “overlap of the actuators” resp. “stiffness ratio of the actuator-surrounding GFRP” and their effect on the target parameters “bending angle”, “shadow width” resp. “air pressure consumption” are analyzed. It could be stated that the “stiffness ratio” only effects the air pressure consumption, but the “overlap” also effects the shadow width. The bending angle itself is, up to ±80°, only limited by the absolute laminate stiffness.

Abstract

Curved, surface-active, shell structures are known for material efficiency and slenderness but typically require complex manufacturing and formwork in combination with intricate on-site construction processes. The presented research proposes an alternative approach: a self-shaping building system for deploying lightweight, curved surface structures made from timber. The system uses the inherent hygromorphic properties of wood which naturally shrinks through drying. This anisotropic shape change is embedded into large-scale bilayer sheets - produced, machined, and shingle clad in a flat state with their later curved shape and connection detailing physically programmed within the material build-ups. When placed on-site, these sheets actuate through air drying to a final curved and interlocked geometry. Geometrically the structure is integratively designed from variable single curved surfaces using key material parameters (end grain angle and moisture content change) within a material stock, in relation to both the self-shaping and the final structural configuration. Each surface is modeled in the curved state using a board specific algorithmic calculation of curvature potential in parallel to a flat fabrication model. Emphasis is placed on investment in early-stage planning and intelligent material arrangement as a method to produce useful curvature. As a result, the curved shell shapes and interlocks without formwork or external mechanical force, with little onsite work. The outcome is a lightweight, longspan roof structure built from single curved wood surfaces with a thin cross-laminated build up. The project demonstrates a tangible new method of low impact, light touch self-construction and an ecologically effective use of material and geometry.

Abstract

Currently, there is a tendency to use Islamic Geometric Patterns (IGPs) as important identities and cultural elements of building design in the Middle East. Despite high demand, lack of information about the potential of IGPs principles have led to formal inspiration in the design of existing buildings. Many research studies have been carried out on the principles of IGPs. However, comprehensive studies relating to new possibilities, such as structure-based, sustainablebased, and aesthetic-based purposes, developed by computer science and related technologies, are relatively rare. This article reviews the state-of-the-art knowledge of IGPs, provides a survey of the main principles, presents the status quo, and identifies gaps in recent research directions. Finally, future prospects are discussed by focussing on different aspects of the principles in accordance with collected evidence obtained during the review process.

Abstract

Adaptive facades can greatly impact a building’s energy balance by responding to external climates and by regulating internal conditions. With the integration of solar energy harvesting components, they have the potential not only to reduce the energy loss of buildings but also to gain energy. This premise has been tested within the framework of bio-inspired compliant mechanisms for adaptive façade elements, developed at the University of Stuttgart. Due to the flexible kinematic behavior of bio-inspired adaptive architectural elements, an innovative and simple alternative to common, more complex applications of adaptive façade components is obtained. The research presented aims at establishing the environmental criteria that will lead to an improved energy performance of a building using elastically deformable, adaptive faҫade elements with integrated photovoltaics. Through simulations and physical testing, the influence of daylight, solar radiation, and the building´s thermal balance are evaluated. The findings of this research are showcased on an adaptive façade consisting of pneumatically actuated, glass fiber-reinforced plastic laminates with integrated photovoltaics, assembled at Botanical Garden in Freiburg, Germany. Relying on environmental sensing, this façade is able to adapt over time in response to solar conditions with the goal of finding the right balance between low-energy building operation, high indoor environmental quality, and high energy harvesting. This study provides a novel, integrative design method utilizing adaptive building envelopes that successfully react to varying environmental conditions in an energy-efficient and cost-effective manner.

Abstract

This paper aims to define the influencing design criteria for compliant folding mechanisms with pneumatically actuated hinges consisting of fiber-reinforced plastic (FRP). Through simulation and physical testing, the influence of stiffness, hinge width as well as variation of the stiffness, in the flaps without changing the stiffness in the hinge zone, was evaluated. Within a finite element model software, a workflow was developed for simulations, in order to infer mathematical models for the prediction of mechanical properties and the deformation behavior as a function of the aforementioned parameters. In conclusion, the bending angle increases with decreasing material stiffness and with increasing hinge width, while it is not affected by the flap stiffness itself. The defined workflow builds a basis for the development of a predictive model for the deformation behavior of FRPs.

Abstract

This paper presents the development of an actively controlled shape changing surface-like structure, where geometric adaptivity is utilised by local elastic deformation on the component level. Besides the physical development of a proof of concept demonstrator, the research proposes a digital form-driving process, a computational workflow which allows the design and fast simulation of the shape changing structure, as well as the digital control of the actuation on the component level. The proposed material system consists of an initially flat surface, which is tessellated into single components based on a hexagonal grid. Each cell is comprised of a three-layer system, where a pneumatic cushion is placed in the middle of two bending active plates with strategic cut outs 1. In this way, each cell can be pneumatically actuated and therefore elastically deformed. The induced bending in the outer plates leads to a controlled change of area – the cells shrink or expand. By controlling this local behaviour within the global arrangement according to principle geometric rules 2 it is possible to achieve a controlled shape change from an initially flat surface to an anticlastic or synclastic geometric configuration. To design, simulate and control the shape change, the authors propose a digital form driving process. Here, the cells are abstracted and simplified into polygons, which can shrink and expand within a given range, according to the proposed physical system. This allows for the fast simulation of different actuation patterns and resulting geometric changes. The abstract values of shrinkage or expansion of each cell can be translated into pressure values and are used to control the pneumatic actuators in the physical demonstrator (figure 1).

Abstract

Adaptive shading devices are of special interest in the context of global need for reducing greenhouse gas emissions. To reduce mechanical complexity of kinetic architectural applications, the investigation of bio-inspired compliant mechanisms has proven to be a promising approach. Thus, a coherent integrative design framework for bio-inspired kinetic folding mechanisms has been developed. This includes the abstraction process of biological principles, such as kinematic behaviours, actuation, as well as materialisation principles. A computational design and simulation model is built to analyse the kinematic and kinetic behaviour of the abstracted biological principles under consideration of specific materialisation and fabrication parameters and constraints. The design and simulation model builds the basis for an automated fabrication process, as well as for interaction and active control of the physical application. The development of the ITECH Research Demonstrator 2018-19, a large-scale compliant folding mechanism, inspired by the folding behaviour ladybug wings (Coleptera coccinellidae), serves as a case study of the developed process. The folding motion of the demonstrator is facilitated by distinct elastic hinge-zones with integrated pneumatic actuators.

Abstract

Regarding modern, daylight-flooded buildings with large window façades, appropriate shading systems to improve the energy consumption of climate controlling systems are becoming more relevant. Building envelopes contribute largely to the temperature control and should be at best installed on the outside to prevent the interior from heating up. Preferably, those systems work with minimum maintenance and maximum robustness, covering as much of the window area as possible. Previous shading systems were mostly based on rigid-body mechanisms using error-prone joints. Components, whose movability is achieved by a local compliance of the material, offer a way to avoid the usage of mechanical joints. Within this paper, a new fiber-reinforced plastic (FRP) façade shading demonstrator called “Flexafold” is presented. Its opening and closing movement are controlled by pneumatic cushions which are integrated directly into the laminate set-up. The Flexafold shows thereby the possibility of producing self‑supporting, adaptive FRP components whose actuators are integrated into the component and thus protected in exterior applications. The functional principles and components of Flexafold, e.g. the locally compliant FRP material, the folding pattern and the integrated actuator system, are explained within this paper. Furthermore, a comparison to existing adaptive façade shading systems “flectofin®” and “Flectofold” is given.

Abstract

Compliant mechanisms of fiber-reinforced plastic (FRP) have been developed to reduce the mechanical complexity of kinetic systems. In a further step, pneumatic actuation was integrated into the set-up of the FRP, offering lightweight, slender, and inconspicuous actuation. Inflation of an integrated cushion causes rotation through the asymmetric material lay-up. Inspiration from the ultrastructure of pressurized veins in arthropod wings has led to the development of a thin layer of elastomer surrounding this pneumatic cushion to avoid delamination. T-peel tests revealed that the elastomer forms a higher adhesion to itself than to glass-fiber-reinforced plastic (GFRP) layers with an epoxy matrix. The angle-pressure relationship for specific GFRP samples with a defined compliant hinge zone was investigated physically and numerically, showing good consistency between the two. Further, a mathematical model, taking into account the bending stiffness of the cushion-surrounding FRP layers, was developed, and a parametric study was conducted on the actuation angles.

Abstract

Hingeless shading systems inspired by nature are increasingly the focus of architectural research. In contrast to traditional systems, these compliant mechanisms can reduce the amount of maintenanceintensive parts and can easily be adapted to irregular, doubly curved, facade geometries. Previousmechanisms rely merely on the reversible material deformation of composite structures with almost homogeneous material properties. This leads to large actuation forces and an inherent conflict between the requirements of movement and the capacity to carry external loads. To enhance the performance of such systems, current research is directed at natural mechanisms with concentrated compliance and distinct hinge zones with high load-bearing capacity. Here, we provide insights into our biological findings and the development of a deployable structure inspired by the Flexagon model of hindwings of insects in general and the hierarchical structure of the wing cuticle of the shield bug (Graphosoma lineatum). By using technical fibre-reinforced plastics in combination with an elastomer foil, natural principles have been partially transferred into a multi-layered structure with locally adapted stiffness. Initial small prototypes have been produced in a vacuum-assisted hot press and sustain this functionality. Initial theoretical studies on test surfaces outline the advantages of these bio-inspired structures as deployable external shading systems for doubly curved facades.

Abstract

Within the collaborative research center Biological Design and Integrative Structures (CRC TRR 141), a research team of biologists, architects and engineers from Freiburg, Tübingen and Stuttgart is working on the development of biomimetic and bioinspired structures for implementation in architecture and building construction. One of the projects in this research center deals with the kinematics of planar, curved and corrugated plant surfaces as concept generators for deployable systems in architecture. It is an example for methods of engineering science at the interface between biology and architecture. The contribution will provide an insight into the process of analyzing the waterwheel plant Aldrovanda vesiculosa, a carnivorous plant that catches its prey by a quick closing movement of a snap trap consisting of two lobes attached to a midrib. At a first glance, the mechanism resembles the one of the famous Venus flytrap; however, it appears to be quite different from a mechanical point of view. In fact, a key aspect in the research presented here is the development of mechanical models and performing corresponding finite element analyses of the plant with the aim to obtain a better understanding of the compliant mechanism of Aldrovanda vesiculosa and its actuation. The latter is related to a change in turgor pressure in a so-called motor zone, adjacent to the midrib, possibly combined with prestressing effects. Apart from this scientific contribution to technical biology or reverse biomimetics, the abstraction of the trapping movement and its implementation in a façade element (Flectofold) as an example of biomimetic architectural design are briefly described.

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.

Abstract

Pflanzen besitzen weder Muskeln noch „klassische“ lokale Gelenke – und können sich dennoch bewegen. Im Laufe der Evolution sind effiziente Bewegungsmechanismen und ästhetische Bewegungsformen entstanden. Aus diesem „Angebot“ der Botanik schöpfen Architekten und Ingenieure in Zusammenarbeit mit Biomechanikern Inspiration für die Entwicklung neuartiger Verschattungssysteme für moderne Gebäude.

Abstract

This paper presents results of the investigation of two biological role models, the shield bug (Graphosoma italicum) and the carnivorous Waterwheel plant (Aldrovanda vesiculosa). The aim was to identify biological construction and movement principles as inspiration for technical, deployable systems. The subsequent processes of abstraction and simulation of the movement and the design principles are summarized, followed by results on the mechanical investigations on various combinations of fibers and matrices with regard to taking advantage of the anisotropy of fiber-reinforced plastics (FRPs). With the results gained, it was possible to implement defined flexible bending zones in stiff composite components using one composite material, and thereby to mimic the biological role models. First small-scale demonstrators for adaptive façade shading systems – Flectofold and Flexagon – are proving the functionality.

Abstract

Plant movements can inspire deployable systems for architectural purposes which can be regarded as ideal solutions combining resilient bio-inspired functionality with elegant natural motion. Here, we first give a concise overview of various compliant mechanisms existing in technics and in plants. Then we describe two case studies from our current joint research project among biologists, architects, construction engineers and materials scientists where the aesthetic movements of such role models from the plant kingdom are analysed, abstracted and implemented in bioinspired technical structures for sustainable architecture. Both examples are based on fast snapping movements of traps of carnivorous plants. The Waterwheel plant (Aldrovanda vesiculosa) captures prey underwater and the Venus flytrap (Dionaea muscipula) snaps in the air. We present results on the motion principles gained by quantitative biomechanical and functional-morphological analyses as well as their simulation and abstraction by using e.g. Finite Element Methods. The Aldrovanda mechanism was successfully translated into a similarly aesthetic and functional technical structure, named Flectofold, which exists in a prototype state. The Flectofold can be used as a façade shading element for complex curved surfaces as existing in modern architecture.