7.2 Ingenieurbau
Filtern
Erscheinungsjahr
- 2023 (44) (entfernen)
Dokumenttyp
- Vortrag (28)
- Beitrag zu einem Tagungsband (10)
- Zeitschriftenartikel (5)
- Buchkapitel (1)
Referierte Publikation
- nein (44) (entfernen)
Schlagworte
- Bahnerschütterungen (3)
- Ground vibration (3)
- Layered soil (3)
- Material moisture (3)
- Offshore (3)
- Shell Buckling (3)
- Wind Energy (3)
- 2-span bridge (2)
- Axle-sequence spectrum (2)
- Bemessung (2)
Organisationseinheit der BAM
- 7.2 Ingenieurbau (44) (entfernen)
Eingeladener Vortrag
- nein (28)
Dieser Kurzvortragg erläutert nichtlineare Phänomene die angesichts der aktuell wachsenden Dimensionen von Monopfahlgründungen für Offshorewindenergieanlagen zunehmend an Bedeutung gewinnen. Insbesondere wird dabei auf das Pfahlfußbeulen sowie das Schalenbeulen des bereits installierten Pfahles eingegangen.
Lehmmauerwerk bietet sich aufgrund seiner zahlreichen ökologischen Vorteile für die Errichtung klimafreundlicher und ressourcenschonender Gebäude an. Um den Anwendungsbereich tragenden Lehmmauerwerks durch eine zeitgemäße Nachweisführung zu erweitern, werden in diesem Beitrag Grundlagen für die Entwicklung eines eurocodekonformen Bemessungskonzepts erarbeitet. Hierzu werden die Ergebnisse umfangreicher experimenteller Untersuchungen an Lehmmauerwerk sowie Lehmsteinen und -mörteln nach Konditionierung bei unterschiedlichen Klimata vorgestellt. Darauf aufbauend erfolgt eine Traglastanalyse druckbeanspruchter Lehmmauerwerkswände mittels numerischer und analytischer Methoden. Die daraus gewonnenen Erkenntnisse werden abschließend in einen an DIN~EN~1996-3/NA angelehnten Bemessungsvorschlag überführt, welcher die materialspezifischen Besonderheiten von Lehmmauerwerk berücksichtigt und eine fundierte Grundlage für eine wirtschaftliche und zuverlässige Nachweisführung darstellt.
The research project Verification of Buckling Assessment and Behaviour in Large Monopiles (VERBATIM) focuses on challenges arising due to the ongoing increase of dimensions of monopiles as foundation for offshore wind turbines. This project is focused on two main topics:
- Monopile tip buckling during pile installation
- Local buckling of embedded piles during operation
It is known from previous investigations and experiences in practice that large deformations of a monopile tip during offshore installation works can occur. These large deformations initiated at the tip of the monopile are commonly referred to as “pile tip buckling”. Own research focuses on optimising monopile dimensions to reduce the cost of monopile foundations for offshore wind turbines while preventing pile tip buckling.
Buckling of embedded cylindrical shells for offshore structures is a common engineering task. Structures can be analysed using standard software and have been done so in recent studies e.g., Gottschalk. However, the trend towards larger monopile and optimised structures has led to a fundamental need for better and verified models. A main challenge is the submodelling of the structure-soil-interaction. Developing such complex models is one main goal of the VERBATIM project.
For both main topics model tests were performed at the laboratories of BAM and TU Berlin. These experimental results were used to verify related numerical models and simulations.
The new crack luminescence method offers the possibility of making fatigue surface cracks in metallic materials more visible during inspections through a special coating system. This coating system consists of two layers, whereby the first layer has fluorescent properties and emits visible light as soon as it is irradiated by UV light. The top layer is black and is designed to prevent the fluorescent layer from emitting if no crack develops in the underlying material.
The technique proved particularly useful in a wide variety of fatigue tests of steel components under laboratory conditions. Moreover, it has the potential to be used in various industrial applications. To enable industrial deployment and integration into maintenance strategies, a concept study is developed in this contribution, resulting in a qualification framework that can serve as a foundation for determining the reliability of the crack luminescence system in terms of a probability of detection curve. Within this study, factors causing measurement variability and uncertainty are being determined and their influences assessed. Due to the extension of the system by a moving computer vision system for automated crack detection using artificial intelligence, additional long-term effects associated with structural health monitoring systems need to be incorporated into an extended probability of detection study as part of the technical justification.
Finally, important aspects and findings related to design of experiments are discussed, and a framework for reliability assessment of a new optical crack monitoring method is presented, emphasizing the influence of various uncertainty parameters, including long-term effects such as system ageing.
The long-term preservation of our infrastructure requires not only intelligent sensor technology and highly developed monitoring procedures, but also innovative digital tools for analyzing, evaluating and utilizing the results. This includes mathematical and, in particular, probabilistic methods for damage detection and tracking as well as for calculating service life and maintenance cycles and data management. The example project Maintal Bridge Gemuenden as part of the AISTEC project shows the workflow for the implementation of structural health monitoring and experimental tests with a train of Deutsche Bahn. The influence lines, as one possible way for damage detection, were measured with a highly accurate GNSS System to locate the trains position when crossing the bridge. The results were compared to measurements from 1987 just before the bridge went in operation.
This presentation deals with the phenomenology and design of pile foundations for offshore wind turbines, and is divided into two lectures.
The second lecture continues with the case of laterally loaded offshore piles, which bears most relevance for the case of the monopile foundations. Here again, a clear separation between physical reality and design methods is intended.
Finally, the last part of the second lecture introduces several advanced topics which lie outside the classical design approaches, namely the hydromechanical coupling effects (i.e. the excess pore-pressure generation around the monopiles), the cyclic pile fatigue and the so-called pile setup (i.e. the time effects on the axial pile capacity). The relevance of the latter two topics is illustrated with experimental results from a field testing campaign on real large-scale piles.
This presentation deals with the phenomenology and design of pile foundations for offshore wind turbines, and is divided into two lectures.
The first lecture presents a brief introduction to the context and peculiarities of such foundations, and then focuses on the particular case of axially loaded piles. This part is most relevant for the relatively slender piles of the multi-pile substructures (i.e. jackets and tripods). A clear distinction between physical phenomenology and practical design is drawn here.
Almost all building materials in civil engineering have an open porosity and interact with or are affected by the environmental conditions. Structures might suffer from effects such as moisture adsorption, carbonation, corrosion, penetration of salt ions and chemical substances, etc. In the hygroscopic range, these processes are mostly driven by diffusion. Due to the confinement of small pores (< 1 µm), the Knudsen effect reduces the molecular diffusion. This reduction can become more significant in case of temporal changing pore systems because of physisorption of water vapor, carbonation, or chemisorption.
In this study, unstabilised earth blocks and earth masonry are investigated. In a first step, the pore size distribution of the blocks is measured and sorption isotherms are recorded in experiments. Besides the ordinary physisorption, the involved clay minerals undergo swelling or shrinking due to chemisorption. The following two effects must be considered: first, the reduction of the available pore space by the adsorbed water layer. For this, the Hillerborg sorption theory is used, which is a combination of the well-known Brunauer-Emmett-Teller sorption theory and the Kelvin equation. This allows the computation of adsorbed water layers even in curved pore geometries. Second, the variation of the initial pore size distribution due to chemisorption needs to be modelled. Based on these two models, the effective diffusion coefficient can be predicted. For validation, arrays of relative humidity sensors were embedded into a free-standing earth masonry wall. This monitoring was carried out over more than a year to have a broad variety of environmental conditions and was located in Berlin, Germany.
The prediction of the effective diffusion coefficient can also be transferred to other processes and allows the investigation of materials having temporarily changing pore systems. Examples are the carbonation of cementitious materials, alkali silica reaction, calcium leaching of long-lasting structures, etc. This effect becomes most prominent in the meso-pore range and might alter the effective diffusion coefficient by more than 100 %.
Almost all building materials in civil engineering have an open porosity and interact with or are affected by the environmental conditions. Structures might suffer from effects such as moisture adsorption, carbonation, corrosion, penetration of salt ions and chemical substances, etc. In the hygroscopic range, these processes are mostly driven by diffusion. Due to the confinement of small pores ( 1 m), the Knudsen effect reduces the molecular diffusion. This reduction can become more significant in case of temporal changing pore systems because of physisorption of water vapor, carbonation, or chemisorption.
In this study, unstabilised earth blocks and earth masonry are investigated. In a first step, the pore size distribution of the blocks is measured and sorption isotherms are recorded in experiments. Besides the ordinary physisorption, the involved clay minerals undergo swelling or shrinking due to chemisorption. The following two effects must be considered: first, the reduction of the available pore space by the adsorbed water layer. For this, the Hillerborg sorption theory is used, which is a combination of the well-known Brunauer-Emmett-Teller sorption theory and the Kelvin equation. This allows the computation of adsorbed water layers even in curved pore geometries. Second, the variation of the initial pore size distribution due to chemisorption needs to be modelled. Based on these two models, the effective diffusion coefficient can be predicted. For validation, arrays of relative humidity sensors were embedded into a free-standing earth masonry wall. This monitoring was carried out over more than a year to have a broad variety of environmental conditions and was located in Berlin, Germany.
The prediction of the effective diffusion coefficient can also be transferred to other processes and allows the investigation of materials having temporarily changing pore systems. Examples are the carbonation of cementitious materials, alkali silica reaction, calcium leaching of long-lasting structures, etc. This effect becomes most prominent in the meso-pore range and might alter the effective diffusion coefficient by more than 100 %.
Ground vibrations near railway lines are generated by the forces that are acting between wheel and rail. It seems to be a straight forward assumption that the vehicle dynamics are important for the level and the frequencies of the excitation forces. Different vehicle dynamics phenomena are analysed for their role in the excitation of ground vibrations: rigid body modes of the bogies, elastic (bending) modes of the car body, and elastic modes of the wheelset. The theoretical analyses use rigid body models, simplified elastic models, and detailed elastic models. Some of these problems are vehicle–track interaction problems where 3D finite‑element boundary‑element models have been used for the track and soil. It is shown that the rigid or flexible vehicle modes are well in the frequency range of ground vibrations (4 to 100 Hz). They have an influence on the excitation force but the additional forces are rather small and can be neglected in ground vibration prediction. The theoretical results are checked by experimental results of a simultaneous measurement of vehicle,
track, and ground vibrations.
Die VDI Richtlinie 3837 enthält detaillierte Angaben zur Erschütterungsemission. Die DIN 45672-3 enthält nur den Tunnel- oder einen Bodenmesspunkt als Ausgangspunkt der Prognose. Die Erschütterungsanregung durch die Fahrzeug-Fahrweg-Wechselwirkung wird beschrieben. Die ERgebnisse der BAM stimmen sehr gut mit dem Prognosekonzept von Highspeed 2 überein. Dies wird an den Punkten 1. Störgrößen, 2. Achsimpulse, 3. Tunnelstrecken aufgezeigt.
Design challenges for Offshore wind-farms. From foundation mechanics to wind-farm aerodynamics
(2023)
This talk provides a brief introduction on general engineering design challenges for the offshore wind energy production. Some general features of the offshore wind-energy field from a civil engineering perspective are firstly presented, followed by a brief discussion of some of the main geomechanical issues for the foundation of the offshore turbines into the seabed.
In the following part, an overview of relevant fluid-structure interactions and some options for an efficient numerical analysis are provided, where the hydromechanical Wave–Tower interaction is firstly discussed. Then, some general aspects of the windfarm aerodynamics are introduced. On the one hand, some modelling possibilities for the wake analysis of single turbines and turbine groups are discussed. And on the other hand the relevance of such analyses for a proper windfarm layout optimization is pointed out.
In particular, this talk shows that: i) The performance and behavior of the turbine's foundation is often conditioned by the appearance of large deformations, fluid couplings and grain-scale phenomena, whereby specific physical testing (both in field and lab conditions) and ad-hoc simulation techniques can provide useful insights for design; ii) Numerical analysis of a turbine’s interaction with wind/waves is already affordable in engineering scales, while simplified models can already provide a useful insight into the windfarm aerodynamics. iii) Turbulent wake analysis is very relevant for the windfarm layout.
The attenuation of wave amplitudes is ruled by the planar, cylindrical or spherical geometry of the wave front (the geometric or power-law attenuation) but also by the damping of the soil (an exponential attenuation). Several low- and high-frequency filter effects are derived for the layering and the damping of the soil, for the moving static and the distributed train loads and for a homogeneous or randomly heterogeneous soil. Measurements of hammer- and train-induced vibrations at five sites have been analysed for these attenuation and filter effects. The measured attenuation with distance can be discribed by generalised power laws and some reasons will be discussed. The theoretical filter effects can well be found in the measurements.