Werner Sobek

Adaptive systems in architecture and structural engineering

This paper presents the research which is carried out in the field of adaptive structures at the Institute for Lightweight Structures at the University of Stuttgart. The application of adaptive systems in the field of architecture and structural engineering creates new chances to design lightweight structures. Different concepts of active control can be used to manipulate the forces, the deflections and the vibration of structures. These concepts are categorised into two groups: control of external loads and control of internal forces. Active shape control can be used to reduce the external wind load by changing the shape of the cross-section of wide-span bridges or high-rise towers. Alternatively active force and/ or stiffness control can be used to manipulate the internal flow of forces and stresses in structures. Systems with active force control superimpose the actively generated forces with the already existing forces, while systems with active stiffness control redistribute the forces according to their varying stiffness distribution. The authors use active elements with variable length and/ or stiffness in static indeterminate structures to control the deflections and redistribute the forces. A bridge with actively controlled elements is presented, where the stress peaks can be reduced and a homogenisation of the force distribution can be obtained.

Plants and Animals as Source of Inspiration for Energy Dissipation in Load Bearing Systems and Facades

From the manifold strategies that nature offers to materials under overload conditions, we describe two: the fibrous and multi-layered system of the bark of the Giant Sequoia, which possesses an impressive damping mechanism, and the spines of pencil and lance sea urchins. The latter introduce a new concept to energy dissipation in brittle construction materials, namely quasi-ductility by multiple local fracturing. The potential for transfer as bioinspired technical solutions is high as the biological role models combine several advantages such as lightweight, recyclability and high protective efficiency. We demonstrate that, in principle, the concepts found in the biological role models can be transferred to concrete-based building materials.

Kinematic modeling of a hydraulically actuated 3-SPR-parallel manipulator for an adaptive shell structure

This paper describes a 3-SPR-parallel robot system with hydraulic actuated prismatic joints that was developed within the context of ongoing research on adaptive shell structures. The potential of adaptive structures is based on the principle of providing means for the system to accommodate a variety of loading conditions (earthquakes, wind, snow) by actively inducing deformations and forces in response to external loads. Thus, stresses and vibrations in the structure are reduced, maintaining or exceeding the performance of passive structures while using much less material and, correspondingly, resources. Adaptive structures, in comparison to traditional systems, contain sensors, actuators, and control systems. One method of actuation is the controlled positioning of the support points of structures. Assuming a statically indeterminate structure, the displacement of the supports will introduce structural deformations and forces. For three-dimensional structures such as the double-curved shell structure under investigation, translational positioning of the support must be provided in all directions. One method to achieve this is the use of 3-SPR-parallel mechanism. The implementation requires a unique and real time solution of the forward and inverse kinematics of the mechanism in order to relate actual displacement of the structural support of the shell to the displacement of the actuators. The solution presented here is based on an analytical approach taking into account the constraint conditions of the 3-SPR-parallel mechanism. The method is validated by numerical analysis of the workspace and then implemented on a reference system.

Energy absorption in functionally graded concrete bioinspired by sea urchin spines

Functionally Graded Concrete (FGC) is fabricated at the Institute for Lightweight Structures and Conceptual Design (ILEK) by using a layer-by-layer technique with two different technological procedures: casting and dry spraying. Functional gradations are developed from two reference mixtures with diametrically opposed characteristics in terms of density, porosity, compression strength and elasticity modulus. In this study the first mixture consists of Normal Density Concrete (NDC), with density about 2160 kg⊙m3 while the second mixture helps to obtain a very lightweight concrete, with density about 830 kg⊙m3. The FGC specimens have layers with different alternating porosities and provide superior deformability capacity under bulk compression compared to NDC specimens. In addition, the FGC specimens experienced a graceful failure behaviour, absorbing high amounts of energy during extended compression paths. The porosity variation inside the layout of tested specimens is inspired by the internal structure of sea urchin spines of heterocentrotus mammillatus, a promising role model for energy absorption in biomimetic engineering.

Optimal sensor placement for state estimation of flexible shell structures

This paper presents a method for optimal sensor placement for flexible shell structures. The optimization objectives are the number of sensors, as a surrogate for implementation cost, and an observability measure. The latter is derived from the observability gramian and considers observation energy of the least observable state. The methodology is tested on a flexible thin-shell structure that is modeled using Finite Element methods. The equations of motion are transformed into modal space and model reduction methods are applied. The resulting model is used for the optimization of the sensor locations. The optimization is performed by the Multi-objective Simulated Annealing algorithm that uses a dominance-based energy formulation for the comparison of different optimal solution candidates.

Active Vibration Control of a Double-Curved Shell Structure Using the Example of Stuttgart Smartshell

The present contribution deals with concepts for active vibration control of a thin double-curved shell structure. The structure, Stuttgart SmartShell, is located at the University of Stuttgart. It is made of softwood and is equipped with strain gages to determine the state of static and dynamic loading. Furthermore a force input is provided at the supports of the structure using hydraulic cylinders. Here a model-based two-degree-of-freedom control concept for vibration damping is presented which is based on a dynamical model derived from Finite Element simulations. The control strategy uses modal decoupling of the system states to enable the manipulation and damping of single eigenmodes. An optimal control strategy is chosen to dampen oscillations as quickly as possible while considering limitations on the force input and peak stresses. The proposed control algorithms are applied to the shell structure under consideration and their applicability is demonstrated by simulation and experimental results.Copyright

Fabrication of Biomimetic and Biologically Inspired (Modular) Structures for Use in the Construction Industry

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.

Adaptive glazing systems - survey of systems

Glazed facade units must satisfy numerous criteria. In addition to allowing an unobstructed view of the exterior they should also provide protection from direct sunlight and the associated heat transfer. In order to optimize the performance of glazed facades under varying conditions, much effort has been directed towards the development of adaptive glazing systems based on smart materials or smart mechanism. This article will outline the functional principles and visual properties of one self-adjusting, thermochromic glazing, two controllable electrochromic systems and one liquid crystal based system.

Potential of origami-based shell elements as next-generation envelope components

Building envelopes manage several crucial functions, including structural, thermal, hygric and aesthetic functions. Classic façade concepts usually work with static elements like glass, metal or composite panels that primarily provide protection against the elements, and an additional layer of active systems that manage dynamic tasks like light protection or thermal regulation. Kinematic shell elements offer new ways to incorporate multiple dynamic functionalities into cladding elements, and thus can help to generate new active, efficient and aesthetic envelopes. We will introduce the concept of origami-inspired multifunctional shell elements and discuss potential applications.

Das Prinzip der Schwesterlichkeit – Mitversorgung von Denkmälern durch Plusenergiegebäude

Die Stuttgarter Weisenhofsiedlung wurde als Wegbereiter des Internationalen Stils weltberuhmt. Am 17. Juli 2016 wurden zwei Hauser der Siedlung, das Einfamilienhaus und das Doppelhaus der Architekten Le Corbusier und Pierre Jeanneret, Teil des UNESCO Weltkulturerbes [1,2]. Die Mustersiedlung bestand ursprunglich aus 21 Experimentalbauten, von denen 10, als Folge des Zweiten Weltkriegs, verloren gingen [3].