Publications

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.

Bridges and roofs are often supported by branched steel columns. Their production is usually expensive and consumes a great deal of energy. In nature, plants manage to form similarly strong and frequently even more complex branch systems through natural growth processes. They can effortlessly withstand mechanical loads, such as their own weight, wind pressure, snow load, or the heavy weight of fruit. In order to find out about the success strategies of ramified trees and shrubs and to learn from them for architecture, we need more than a detailed look at the form of ramification and inside the plants. We also need computer models and new materials and methods for the production of branched support structures in building construction to succeed in transferring the biological concepts to technology.

Natural structural systems that have developed over millions of years illustrate how large loads can be absorbed with very little material. This is achieved by adapting the structural properties to a predominant load profile. If we succeeded in transferring these principles to structures created by people, it would be possible to significantly reduce the consumption of resources in the construction industry. As a contribution to this, the Rosenstein Pavilion was developed based on bio-inspired optimization strategies in order to demonstrate the potential of resource-efficient building.

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.

Biology can provide exciting ideas for the development or improvement of technical products. As a rule, the underlying principles are first investigated using a feasibility demonstrator, which does not represent a finished technical product but nevertheless, on the whole, is intended to “function” like the finished product. However, there is a long way to go from this first prototype to a product that is ready to use or to a convincing building method. In this process, numerous ideas that at first seem interesting and promising have to be abandoned. Many aspects must be investigated in parallel, and plausible solutions need to be found, not only in terms of reliable and durable functionality, but also in terms of commercial viability and resource-efficient manufacture. In addition, it is important that an innovative product is accepted in the market. In the case of architecture, this means-above all- that the product is esthetically appealing, because without that aspect, there will not be much interest even if the product functions well.

Plants have neither muscles nor “classic” local joints-and yet they can move. In the course of evolution, efficient movement mechanisms and esthetic movement forms have developed. Architects and engineers, in cooperation with biomechanists, are benefiting from this botanical “offering” and drawing inspiration for the development of new types of facade shading systems for modern buildings.

Nature creates efficient, complex structures using the smallest possible amount of material. The construction principles employed and the intelligent use of materials regarding their specific properties can be transferred to modern production methods. The objective is to produce functional low-weight building components that consume as few resources as possible. In this chapter we show how this bionic transfer takes place by continuing the development of production methods, such as fiber technology (pultrusion, fiber deposition), 3D printing, the manufacture of concrete components, and a combination of these three methods.

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.

Based on a textile technology known from carpet manufacturing (tufting) respectively z reinforcement of fibre-reinforced plastics (FRPs), a new process has been developed for interface connections between two FRP component parts: tufting of pre-fabricated FRP pins during preform manufacturing. Both preform and tufting loops are impregnated simultaneously. Afterwards so called "tufting pins" protrude out of plane of the FRP plate or into the inside of a 3D FRP hollow structure, for example a cylindrical component. The hollow structure can be filled with a core material in particular to enhance mechanical properties. In the case of micro-gaps caused e. g. by shrinkage of the material the pins close these micro-gaps between core and FRP-hull or rather maintain mechanical contact between hull and core. In extensive tests the general adhesion properties between pinned FRP and concrete as a filling material as well as the influencing variables of the tufting process with regard to their effects on mechanical parameters were investigated. Decisive influencing factors result both from the textile process as well as the component design. It is shown, how the tension load of a tufted FRP connection increases depending on the reinforcing fibre material as well as the number of tufting pins.

Within the collaborative research center Transregio 141 ‘Biological Design and Integrative Structures. Analysis, Simulation and Implementation in Architecture’, the authors work in an interdisciplinary team composed of biologists, structural engineers, and textile engineers developing novel technical branchings as structural elements for architecture inspired by branchings in nature. Branchings are common in structures of plants and construction and have to fulfill structural demands in both fields. As resource efficiency is a vital factor allowing plants to resist competitive stress, beneficial load-bearing principles found in plants might, in an abstracted manner, also improve technical support constructions. To discover these principles, the biomechanics of selected plant branchings were investigated by FE-simulations. The observed principle of continuous fiber courses from the stem into the branch yields stiff and strong connections also favored in artificial joints. The key challenge is to produce technical branchings with a continuous fiber arrangement. This is enabled by a newly developed braiding process for branched structures. The design of the branched large-scale demonstrator at the Museum of Natural History in Stuttgart for the exhibition ‘baubionik’ (construction-bionics) reveals the potential for future architectural applications with individually variable knot geometries. The findings of the investigation mark a starting point for a novel braided concrete-fiber-reinforced plastic composite construction for branched supporting columns with both high aesthetical and load-bearing demands as a potential competitor for current construction methods of cast steel knots or labor-intensive welded steel pipe joints.

Fiber-reinforced materials offer a large improvement in structural performance if specific load cases can be determined. In aerospace, lightweight structures are crucial because of launcher limitations. For academic purpose CubeSats are a powerful concept to participate in space research on a low-cost-level. Reducing the structural mass, while keeping the mechanical performance, provides a bigger payload mass budget. Additionally, there are several types of payloads that do not fit in common structural components. Inasmuch as CubeSats are mainly used in research, such systems change substantially, so that an easily adaptive method would be beneficial to be no longer restricted by prefabricated structural components. The developed rapid prototyping technology tackles these issues by having an automated 3D deposi- tion method which can produce extremely lightweight as well as geometrical- and load-adaptive primary structures with minimum space requirements. A fiber deposition head for a six-axis robot has been devel- oped to impregnate and wind a single carbon roving on a frame to produce 3D integral components. The geometry of the frame can be adjusted to the required application by introducing holes or attachment points at nearly any position. Its modular layout varies, so that it only can be fabricated economically by fused deposition modeling and removed after resin curing easily. Furthermore, by blending additives into the resin it is possible to create material gradient components. Hence adaptiveness can be generated e.g. in terms of solar energy absorption. Compared with 1U aluminum wall structures available on market a carbon fiber-reinforced plastics (CFRP) winded structure results in a mass saving of 45% for a solid and 76% for a skeletonized wall segment, premised on calculations for two layers of CFRP made of 24K rovings with a fineness of 1600 tex at a fiber-volume-fraction of only 50%. This concludes that maximum potential can only arise with optimized fiber path generation. Costs can be saved in terms of material (no fiber blend), molding (3D printed frame), design of fiber path (sys- tematic guidelines), assembly (integral design) and manufacture (robotic production). The advantages will be demonstrated with a generic non-in-situ-sensory 1U CubeSat because it is easy to compare it to other systems due to the strict design specifications. The paper will include detailed information on the design of the robotic fiber deposition head, the modular and adjustable frame, the winding pattern generation and the mechanical testing.

In modern architecture branched supporting structures are increasingly used. Until now, these branched columns can only be produced in an extensive and cost-intensive way. A new concept made of fibre-reinforced plastic (FRP) serving as a formwork and a load-bearing hull for a concrete core makes it possible to produce a wide variety of different forms and geometries. To enable the potential of complex branched geometries, especially continuous load-confirming fibre arrangements over the entire braiding hull and large diameters, an advanced braiding technique to create triaxially braided preforms is required. This paper focuses on recent developments of an advanced braiding process to fabricate a multi-layered complex structural geometry on a 144 bobbins radial braiding machine and the adaptation of stationary threads until now regulated by spring force into ones operated electronically. With the new braiding technique, branched performs with triaxial braids were produced. Subsequent to impregnation with a thermosetting resin and annealing, the FRP-hull is poured with concrete. To evaluate a potential load increase of load capacity of the concrete core due to the confinement of FRP-hulls compression tests are conducted. In comparison to plain concrete specimens the mechanical parameters of fibrereinforced plastic-concrete-composites show a significant increase in compression strength.

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.

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.

Brücken und Dächer werden oft durch verzweigte Stahlstützen getragen. Diese sind in ihrer Herstellung meist teuer und energieaufwendig. In der Natur gelingt es Pflanzen, ähnlich stabile und häufig noch komplexere Verzweigungen durch natürliche Wachstumsprozesse zu bilden. Sie können mechanischen Belastungen mühelos standhalten, wie zum Beispiel ihrem Eigengewicht, Winddruck, Schneelast oder schweren Früchten. Um den Erfolgsstrategien verzweigter Bäume und Sträucher auf den Grund zu gehen und von ihnen für die Architektur zu lernen, bedarf es nicht nur eines genauen Blicks auf die Form der Verzweigung und ins Innere der Pflanzen. Auch Computermodelle sowie neue Materialien und Methoden für die Herstellung verzweigter Stützstrukturen im Bauwesen sind für solche Übertragungen in die Technik notwendig.

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.

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.

Die Natur schafft komplexe, effiziente Strukturen bei minimalem Materialverbrauch. Die dabei verwendeten Bauprinzipien mit intelligentem Einsatz von Materialien und deren spezifischen Eigenschaften lassen sich in die moderne Fertigungstechnik übertragen. Ziel ist, deutlich leichtere, funktionale Bauteile ressourcensparend herzustellen. In diesem Kapitel zeigen wir, wie dieser bionische Transfer durch die Weiterentwicklung von Fertigungsverfahren wie der Fasertechnik (Pultrusion), dem 3D-Druck, der Betonteileherstellung und einer Kombination dieser drei Techniken abläuft.

In technical constructions, movements are usually achieved by articulated rigid elements. In such cases, the most common cause for failure is mechanical abrasion. Plants are able to perform reversible movements without employing “true” hinges and possess an anisotropic material structure. Moreover, plants generally mechanically adapted to local stress- and strain-concentrations. By this, plants are of high interest for the field of biomimetic architecture since deployable structures, e-g- common shading systems, usually incorporate “classical” technical hinges. The internal structure of plants resembles fiber reinforced plastics (FRPs) consisting of a shaping matrix enveloping reinforcing fibers. By using FRPs in construction engineering, it is possible to generate anisotropic properties within defined regions so that stiff and elastically deformable areas in one component are achievable. The movement principle of traps of the aquatic, carnivorous plant Aldrovanda vesiculosa (waterwheel plant) serves as inspiration for a bio-inspired shading system, Flectofold.

In architecture and construction engineering, a vast number of connections and branched columns in frame structures exist that are exposed to high static and dynamic loads. The manufacture of many of these elaborate structures is both time-consuming and costly. Industry has no solution for cost-effectively producing aesthetic and mechanically stable branched columns. This challenge is addressed by the development of branched structures inspired by branched biological concept generators such as Schefflera arboricola. Here, we present methodological approaches allowing the reconstruction of the outer shape and inner structure of complex branching regions, such as in S. arboricola, by using and combining three-dimensional-image stacking of histological thin sections, micro-computer-tomography (μCT) imaging and laser scanning. Computer-aided design (CAD) and Finite Element (FE) models of such structures can then be produced that not only help to provide a better understanding of the functional morphology and biomechanics of the biological concept generator, but also render the basis for the intended biomimetic transfer to branched columns consisting of a braided hull filled with concrete. The current project results are mainly based on the analysis of S. arboricola branching and the results of a previous research project (SPP 1420) in which biomimetic branched fibre-reinforced plastic (FRP) columns inspired by the branching structure of Dracaena were produced. Currently a biomimetic hull geometry that can be manufactured industrially is developed. Initially, branched FRPs based on triaxial braids with readily adjustable mechanical properties are filled with concrete and thus shall achieve sufficient mechanical properties for application and cost-effective fabrication in the building industry.

A pultrusion process for producing spatial continuous fiber reinforced plastic profiles with uv-curing resins has been developed. Instead of using a rigid steel die, a uv-transparent flexible die has been used which allows a broad variety of bending radii. This development was driven by the need for concrete armory following the flux of force for the use in porous gradient concrete. The usage of fibers other than transparent glass fibers like carbon- and basalt fibers in combination with uv-resins was made possible through the utilization of peroxides. For material characterization purpose straight profiles made of glass and basaltfibers were produced. Subsequently a process to produce spatial profiles was developed.

The transformation of biological paradigms into building construction involves the transfer of structure and system-defining properties from biological role models to construction-specific and innovative non-construction-specific systems and processes. The challenge of manufacturing biomimetic and bio-inspired structures includes the provision of methods and procedures that allow the mapping of biological features on a production-related description. The methodological approach requires the validation and verification of existing production methods at the small scale (model, elementary cell) in order to transfer findings to the production of components at the construction scale. Additionally, the biological features that cannot be reproduced by existing methods require further adjustment or the development of new methods for appropriate transfer. A basic condition for the further development of such production procedures is the possibility of manufacturing complex structures based on biological strategies concerning resource and energy consumption, waste production and greenhouse gas emissions.

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.