FG Hybride Konstruktionen - Massivbau
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This paper presents a recently developed joint for timber-concrete composite frames. The developed joint was studied in terms of its ability to transfer bending moments, normal and shear forces resulting in a frame structure under horizontal and vertical loads. Several aspects are taken into account during the development and manufacturing process such as the material-appropriate use and a simple assembly concept. A series of experimental full-scale tests, with extensive measurements, were conducted consisting of five test specimens to investigate the static properties of the joint construction. The focused properties are the bending and rotational capacity as well as a ductile beam-to-column connection. For all specimens beech laminated veneer lumber was used, varying the geometric dimensions of the column and composite beam as well as the concrete strength. In addition to the experimental investigations, a numerical model was developed and validated using local strains, global deformations and rotational stiffness. Relevant numerical input parameters, which were not determined experimentally, were investigated as part of a numerical parameter analysis.
New fire design approaches enable innovative load-bearing and bracing concepts for tall buildings made of timber. As a renewable building material, timber in combination with concrete is currently setting new heights and at the same time offers a high CO2 saving potential. Usually, timber-concrete composite structures are mainly used in the floor slabs to ensure sound insulation and fire protection. This paper presents a newly developed beam-to-column joint for timber-concrete composite frames, which has been studied in terms of its ability to transfer bending moments, normal and shear forces. A series of full-scale experimental tests were conducted to investigate the structural properties of the joint design. In addition, all specimens were analysed numerically to verify the load transfer mechanisms. As an overall result, the test specimens showed a ductile behaviour beyond their primary failure. Finally, hybrid multi-story frame systems with rigid beam-to-column connections can be used for structural bracing of mid-rise buildings and efficiently combined with an (excentric) core for high-rise buildings.
Steel bridges as slender and highly articulated lightweight structures are exceedingly exposed to fatigue damage due to traffic. Especially railway traffic is causing significant stress variations, the material can only withstand a limited amplitude and number of stress cycles. This results in a reduced lifetime of the bridge. This paper gives an overview of the material behaviour of steel due to fatigue. The lifetime capacity of an existing bridge as reference is analysed according to the current state of technology based on a simplified FE-Model. Further, the potential for extending the lifespan by reducing the vibration cycles through additional damping is numerically investigated for the referred bridge. A possible direct correlation between fatigue-relevant stress and the remaining service life of the existing bridge is demonstrated.
In structural engineering, active structures that combine the principles of lightweight construction with flexible component behavior are increasingly being realized. Within this approach, the lightweight design offers material-efficient structures which, due to their reduced mass, provide a good basis for an energy-efficient actuation. In addition, the use of flexible component behavior provides the possibility to keep the number of required actuators as low as possible, while maintaining a high degree of adaptability. Therefore, the resulting active hybrid structures represent a promising approach with respect to the development of sustainable active structures in our built environment. Due to a larger number of relevant objectives, this new kind of structures requires a higher design effort compared to classical structures from the field of structural engineering. This dissertation aims to contribute to a more efficient and generalized design process for active hybrid structures. In order to achieve this goal, several strategies have been investigated. First of all, useful target criteria related to the mentioned relevant areas are derived. These should enable a more target-oriented design and provide a basis for formulating appropriate target weighting, allowing the development of ideal compromise solutions that combine structural stiffness, bending elastic transformation behavior and an efficient actuation concept. In addition, a variety of approaches have been investigated to improve the design process of active hybrid structures in a broad stress field between stiffness and compliance. These mainly include the aspects of structure generation, analyses for an optimal load transfer as well as the determination of an associated optimal actuation concept. In the context of this thesis, different subroutines are investigated for the mentioned partial steps of an overall hierarchical method which were implemented in a software application. Some variations of this generalized method were applied to diverse structural case studies of cantilevered systems with different degrees of structural stiffness. Three of these examples, representing segments of roof structures that differ in terms of their bending elastic transformation behavior, were analyzed in more detail in this thesis. These analysis results were verified on real active hybrid prototypes.
Elastic kinetics are an approach to design transformable lightweight structures with a stable transformation process. The transformation is realized through elastic bending of structural members by exploiting the compliant material behavior. This lightweight and flexible design comes at the cost of increased sensitivity to static and dynamic disturbances. However, most of the current research focuses on the principles of elastic kinetic transformation instead of effective disturbance mitigation. This work focuses on dynamic disturbance mitigation for such transformable lightweight structures using active control. Modeling and controller synthesis are performed in the linear parameter-varying (LPV) framework, since the dynamics of elastic kinetic structures are transformation-state dependent due to geometric nonlinearities. Based on an LPV model in a grid-based representation, an LPV output-feedback control can be designed and synthesized via a gridding approach. This methodology is experimentally tested and validated for the example of an active hybrid roof structure prototype.
Ressourcen- und energieeffiziente Konstruktionen : 28. Brandenburgischer Bauingenieurtag BBIT 2024
(2024)
Der 28. Brandenburgische Bauingenieurtag 2024 an der BTU Cottbus-Senftenberg widmet sich den angestrebten Zielen einer Ressourcen- und Klimaneutralität. Möglich wird dies durch innovative Ansätze und interdisziplinäre Planungs-, Bau- und Betriebsprozesse. Die Referenten zeigen Herausforderungen und Lösungen bei der Entwicklung klimaneutraler Baustoffe und Bauteile sowie deren Weiterverwendung und Kreislauffähigkeit. Darüber hinaus werden Erkenntnisse zur Ertüchtigung und Erhaltung vorhandener Bausubstanz sowie zu leichten, hybriden und adaptiven Konstruktionsansätzen vorgestellt.
Das hier bearbeitete Forschungsprojekt leistet einen ersten Beitrag zur Entwicklung von biegetragfähigen Holz-Beton-Verbundknoten in Rahmentragwerken zur Aussteifung von Hochbauten. Rahmentragwerke liefern architektonische Vorteile in der Grundriss- und Fassadengestaltung von Gebäuden durch den Wegfall von aussteifenden Verbänden und Schubwänden und sind damit besonders für eine spätere Umnutzung geeignet. Die Entwicklung der hier betrachteten Rahmenknoten basiert auf dem Lastabtrag mehrfeldriger und mehrgeschossiger ebener Rahmensysteme. Der lokale Lastabtrag in der Knotenkonstruktion konnte im ersten Schritt des Projektes auf Grundlage von Stabwerksmodellen visualisiert und nachgewiesen werden. Es wurde darauf geachtet, die verwendeten Materialien – Holz, Beton und Stahl – werkstoffgerecht einzusetzen, um eine größtmögliche Tragfähigkeit zu erzielen. Rahmentragwerke gelten aufgrund der konzentrierten Lastabtragung in den Knoten als hochbeanspruchte Tragwerke. Daher wurde ein hochfestes Buchenfurnierschichtholz der Firma Pollmeier Furnierschichtholz GmbH verwendet, welches eine etwa 3-mal höhere Biegefestigkeit als konventionelle Nadelhölzer aufweist. Zur Untersuchung der statischen Eigenschaften wie Lastabtragungsmechanismen, Grenztragfähigkeiten und Rotationssteifigkeiten wurde eine Versuchsserie mit insgesamt 6 Versuchskörpern im realitätsnahen Maßstab erarbeitet. Die einzelnen Versuchskörper unterscheiden sich in den geometrischen Abmessungen der Riegelquerschnitte, im Stützenanschluss und der Festigkeit des Verbundpartners Beton. Zur besseren Vergleichbarkeit wurden die Betone in der Forschungs- und Materialprüfanstalt (FMPA) der BTU Cottbus-Senftenberg selbst hergestellt, mit dem Ziel vergleichbare Werkstoffeigenschaften zwischen den einzelnen Versuchskörpern zu erzielen bei denen der Beton nicht der Variationsparameter ist. Im Sinne einer nachhaltigen Kreislaufwirtschaft wurde auch untersucht, ob sich Recyclingbeton für die statischen Anforderungen in der Rahmenkonstruktion eignet. Die einzelnen Versuchskörper wurden zum weiteren Erkenntnisgewinn numerisch mit Hilfe der FE-Software Ansys Workbench untersucht. In den räumlichen Modellen wurden, für möglichst realitätsnahe Simulationen der experimentellen Versuche, die materiellen und kontaktbedingten Nichtlinearitäten berücksichtigt. Die numerischen Ergebnisse wurden anschließend anhand der experimentellen Ergebnisse validiert. Die Herstellung der Versuchskörper und die experimentelle Versuchsdurchführung erfolgte in der FMPA. Auf Basis der numerischen und experimentellen Erkenntnisse konnten anschließend maßgebende Versagensstellen identifiziert und ein analytisches Konzept zur Bestimmung der Tragfähigkeit erarbeitet werden. Auch wurden signifikante Verformungskomponenten benannt und zu einem analytischen Gesamtfedermodell der Knotenkonstruktion nach Vorbild der Komponentenmethode aus dem Stahl- und Stahl-Beton-Verbundbau zusammengeführt. Durch ein erstes Gesamtfedermodell kann aus den Verformungen der Komponenten die Rotationssteifigkeit berechnet werden. Das analytische Gesamtfedermodell wurden abschließend mit den experimentellen Ergebnissen validiert. Den Abschluss des Forschungsprojektes bilden Empfehlungen zur Ausbildung duktiler Rahmenknoten im Holz-Beton-Verbundbau auf Grundlage der experimentellen, numerischen und analytischen Ergebnisse.
The linear parameter-varying framework for active vibration control of elastic kinetic structures
(2024)
Lightweight design is essential for preserving resources, and in addition, transformability can be beneficial for specific applications where multi-functionality is required. Multi-functionality contributes to saving resources by allowing multiple purposes to be served effectively and by allowing adaptation to changing needs. Elastic kinetics are a recent approach to design transformable lightweight structures with a stable transformation process, realized by elastic bending of structural members. Their lightweight and flexible design comes at the cost of increased sensitivity to static and dynamic disturbances. However, most of the current research concentrates on transformation principles instead of on disturbance mitigation.
This research focuses on dynamic disturbance mitigation for transformable lightweight structures based on elastic kinetics using active control. The dynamic behavior of such structures is transformation state dependent due to geometric nonlinearities, which is not easily captured by linear time-invariant methods. For this reason, modeling and control design are performed in the linear parameter-varying (LPV) framework. Thereby, two distinct LPV modeling methodologies are investigated, one based on finite element models and another utilizing experimental system identification techniques. Furthermore, LPV control strategies are introduced, which allow to adapt to the varying structural dynamics encountered in elastic kinetics. To validate the efficacy of the modeling and control approaches, a physical demonstrator resembling a segment of an elastic kinetic roof structure is realized within a laboratory environment. This demonstrator structure is used for experimental studies to assess the accuracy and performance of the introduced methods.
Utilizing experimental data from the demonstrator structure, a proposed LPV system identification methodology can be applied to derive separate LPV models for the bending and the torsional dynamics of the demonstrator structure. Based on the derived LPV models, a decoupled active vibration control for bending and torsional dynamics by means of an LPV output-feedback is designed. The designed control is implemented on a real-time environment, and its effectiveness is demonstrated experimentally for fixed and for varying operating conditions on the realized demonstrator structure.
The distributed-Multiple Tuned Facade Damping (d-MTFD) system was proposed to effectively reduce wind-induced vibrations of high-rise buildings by using the parallel moveable outer skin of the Double-Skin Facade (DSF) as damping mass. A full-scale prototype with a moveable (kinetic) DSF element has been built for first experimental tests using Hardware-in-the-Loop (HiL) simulations. The parallel moveability of the DSF’s outer skin is achieved by mounting it on a smooth-running guide rail system. A stepper motor is applied as an adjustable electrical damper and simultaneously serves as an energy harvester. By using grey-box system identification, all the parameters of the prototype can be accurately estimated. For example, a low equivalent friction ratio of 0.0022 was estimated. The identified model achieved high fitness values (80% to 91%) compared to the measured data, providing the basis for the reliability of the experimental tests using HiL. The prototype is the hardware part of the HiL simulations, which is connected to the simulation part, namely, a 76-story, 306 m high benchmark building assumed to be installed with the d-MTFD system. The feasibility of using a stepper motor as an adjustable electrical damper for semi-active control has been successfully validated based on the HiL simulations. By using semi-active control, the relative displacement of the DSF’s outer skin can be significantly reduced by about 35% compared with using passive control. Energy harvesting performance has also been investigated. The average energy harvesting efficiency of the power electronics was experimentally determined as approximately 75%. With consideration of all the parasitic damping in the connection, the average energy harvesting efficiency was about 50%. For tests under across-wind excitation with a return period of 10 years, the self-sufficient operation of the semi-active d-MTFD system was proven to be achievable based on the prototype results. The average harvested power of the whole benchmark building (with 1000 moveable facade elements) can be predicted as 1.3 kW.