7.2 Ingenieurbau
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The soil-foundation-structure interaction is always important when building vibrations due to train passages have to be considered. The frequency range for train vibrations is up to 100 Hz. Normally, soft surface soils are crucial so that the wavelength can be much smaller than the foundation dimensions. Three topics are of interest for the prediction and the under-standing of building vibrations. 1. The „kinematic interaction“ or the „added foundation ef-fect“, which is calculated either by the combined boundary-element finite-element method or by the wavenumber domain method, results in a reduction of the free-field vibration. The stiff-ness of the foundation resists the wave deformation, plates and walls for horizontally propa-gating waves or piles for vertically incident waves. 2. The „inertial interaction“ or the „added building effect“ yields an amplification around the vertical building resonance, which may be a rigid mode on the compliant soil or a flexible mode for high-rise buildings, and a reduction at higher frequencies. This has been analysed by detailed finite element models of apartment and office buildings. 3. Base isolation is a method to further reduce building vibrations. It is important to know the soil-foundation impedance for the possible reduction, as well as the correct building impedance. A high-rise building cannot be considered as a rigid mass model. It has a frequency-dependent behaviour with longitudinal waves travelling from the founda-tion to the top of the building which include the effect of floor vibrations. Experiences from building projects in Vienna, Frankfort and Berlin will give some additional results for the ex-citation from tunnel lines, the kinematic response of pile foundations, and the inertial re-sponse of the flexible multi-storey buildings.
The resonances of railway bridges have often been analysed for short bridges under periodical high-speed trains, for simply supported one-span bridges, for the fundamental bridge mode, and by time-domain analyses. Many time-consuming calculations have been performed to establish simplified rules for standards. In this contribution, the passage of different (existing, new and hypothetic) trains over different bridges will be analysed in frequency domain by using three separated spectra with the purpose to get a better physical insight in the phenomena. At first, the excitation spectrum of the modal forces is built by the mode shape and the passage time of the train over the bridge. The second spectrum is the frequency response function of the bridge which include the modal frequency, damping and mass. The third part is the spectrum of the axle sequence of an arbitrary train which is not limited to periodical or specific (conventional, articulated, regular or standard) trains and which does not include any bridge parameters. The final solution in frequency domain is obtained as the product of these three complex, strongly varying spectra for the dominating bridge mode or in general as the sum of these products over all relevant bridge modes. The time domain solution is obtained via the inverse Fourier transform, and the resulting time histories have been successfully compared with some measurement results. The method is applied to the vertical and torsional modes of a mid-long 1-span bridge on elastomeric bearings under standard train speeds, and to a long multi-span integral bridge under long periodical freight trains. Different resonance and cancellation effects have been found for systematically varied train speeds according to the axle sequence of the whole train which is dominated by the two locomotives in that case. To be more specific, the first torsional mode of the mid-span bridge is excited for a train speed of 100 km/h whereas the second bending mode is excited for a train speed of 160 km/h. In both cases, the other mode is suppressed by the minima of the axle-distance spectra. In addition, the case of the German high-speed train ICE4 and the very high-speed hyperloop case will be discussed briefly. In general, it is shown that resonance effects are also worth to be studied for freight and passenger trains with lower speeds.
Train-induced ground vibrations – The emission and transmission from tunnel and surface lines
(2023)
Train-induced ground vibrations are quite different for tunnel and surface lines. The excitation of the track and ground vibration by the vehicle-track-soil interaction maybe influenced by the stiffer track support of the tunnel invert. The excited waves are propagating on a different path compared to the surface line. The wave propagation in the interior of the soil is calculated by a wavenumber integral in a similar way as the propagation along the surface and a general reduction of < 0.5 has been found. An additional reduction has been found because of the missing Rayleigh wave. The different excitation of tunnel lines is analysed theoretically by the combined finite-element boundary-element method and some results about the influencing tunnel and soil parameters will be shown. Measurements have been made at the Mühlberg-Tunnel in Germany. The vibrations of the train, the track and the soil have been measured simultaneously at the tunnel and a nearby surface line. Spectra will be shown for different train speeds between 60 and 160 km/h. A clear reduction effect for the tunnel line compared to the surface line has been observed in a specific (train-speed-dependent) frequency range. This agrees well with the observations of other research institutes. The mid-frequency tunnel-surface reduction seems to be a consequence of the stiffer track structure which leads to a wider distribution of the axle loads. Therefore, the axle impulses due to the train passage are longer and have a lower frequency content. This will have an effect on the ground vibrations at some distance which are present in case of an irregular transmission path through a ballast and soil with varying stiffness. A similar reduction effect can also be found for other track forms where the axle impulses are distributed on a longer track segment, for example slab tracks, tracks with under ballast plates, under ballast mats or under sleeper pads.
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.
The contribution shows measurement examples of cars, floors, foundations, railway tracks, a footbridge, and a railbridge. Vibrations may include modes and waves. Namely in soil-structure interaction, modes are damped, shifted and prevented so that alternatives for the modal analysis are necessary: The approximation of the whole spectrum (flexibility function) and of the whole train passage (moving-load response).
Die Prognose und Minderung von Bahnerschütterungen haben eine lange Tradition in der Bundesanstalt für Materialforschung und -prüfung. Im Jahr 2006 wurde eine Prognose-Software fertiggestellt, die viele Forschungs- und Messergebnisse zusammenfasst. Sie umfasst die Teilbereiche Emission (die Anregung durch die Fahrzeug-Fahrweg-Untergrund-Wechselwirkung), die Transmission (die Ausbreitung durch den Boden) und die Immission (die Übertragung vom Freifeld in ein Gebäude). Die Prognose geschieht in allen Teilen mit einfachen Formeln, die veröffentlicht sind und zur Anwendung für Jedermann zur Verfügung stehen. Es werden Beispiele zur Emission und zur Transmission gezeigt.
Im Bereich Transmissionsprognose werden zu den Anregungskräften (aus dem Emissionsteil) die Bodenerschütterungen als Schwinggeschwindigkeitsterzspektren berechnet. Das Ergebnis hängt stark von der Bodensteifigkeit, -dämpfung und -schichtung ab. Dies wurde später mit einer Messkampagne in der Schweiz an 10 Messorten bestätigt (Bild 1). Die Berechnung erfolgt näherungsweise für einen geschichteten Boden mit einer frequenzabhängigen Wellengeschwindigkeit (Dispersion) oder einem tiefenabhängigen Wellengeschwindigkeitsprofil.
Die Anregungskräfte werden im Prognosebereich Emission mit einem 2-dimensionalen Gleismodell berechnet (Bild 2). 1-dimensionale Modelle liefern meist falsche Ergebnisse und 3-dimensionale Modelle (zum Beispiel mit der kombinierten Finite-Element-Randelement-Methode) sind für eine Erschütterungs¬prognose sicherlich zu aufwändig. Das 2-dimensionale Modell wurde an 3-dimensionale Ergebnisse so angepasst, dass die Ergebnisse für viele Gleise und Böden annähernd zutreffen. Auch Minderungs¬maßnahmen am Gleis können mit diesem Modell sehr gut berechnet werden.
Die Prognoseverfahren wurden in den folgenden Jahren weiter verfeinert. Es wurde die quasi-statische Anregung durch die bewegten statischen Zuglasten mit einer Näherungsformel ergänzt, so dass auch das tieffrequente Nahfeld realistisch erfasst werden kann. Mit der Berücksichtigung der Achsfolge (insbesondere zwischen den Achsen im Drehgestell) ergeben sich zwei typische Minima in den Erschütterungsspektren, die oft auch in den Messungen beobachtet werden. Der Amplitudenanteil zwischen diesen beiden Minima ist oft stärker angehoben, so dass hier eine zusätzliche Erschütterungsanregung vermutet wird. Dieser Anteil kann rein empirisch prognostiziert werden, so wie das in den englischen Prognosen (zuletzt für das Highspeed2-Projekt) enthalten ist. Die Begründung dieses Anteils ist allerdings nicht die Achsfolge, sondern die Zerstreuung der statischen Achslastimpulse durch einen unregelmäßigen Gleisuntergrund und Boden.
Die messtechnische Ermittlung eines Minderungseffektes ist komplizierter als allgemein angenommen. Es reicht nicht aus, jeweils an einem Messpunkt in der Nähe eines Gleises mit und ohne Minderungs¬maßnahme die Erschütterungen zu messen und aus dem Verhältnis der Amplituden (beziehungsweise aus der Differenz der Pegel) „die Einfügedämmung“ zu ermitteln. Es wird an Beispielen gezeigt, wie man hier sinnvoller vorgehen kann.
1. Zunächst ist es wichtig, nicht nur die Einfügedämmung sondern auch die Originalspektren mit und ohne Minderung zu dokumentieren und zu veröffentlichen, damit man kontrollieren kann, ob wesentliche Amplituden und Frequenzbereiche reduziert sind oder ob es sich um eher zufällige Minderungen oder Verstärkungen handelt. (Beispiel Unterschottermatte/Raron, Müller/SBB)
2. Der Messpunkt sollte nicht im Nahbereich des Gleises liegen, da ansonsten eine zu günstige, falsche Einfügedämmung bestimmt wird. (Beispiel Tunnel/ Leipzig/Breitsamter)
3. Um Zufälligkeiten zu vermeiden, sollte man an mehr als einem Punkt messen. (Beispiel Unterschotterplatte/Altheim/Auersch)
4. Man sollte eigentlich immer auch die Bodenkennwerte (Steifigkeit, Dämpfung, Amplituden-abnahme, Übertagungsfunktion) messen. Selbst bei nahegelegene Messquerschnitten kann man Überraschungen erleben. (Beispiel erste ICE-Messungen/bei Würzburg/Auersch)
5. Bei verschiedenen Bodenkennwerten kann man eine Korrektur durchführen. (Beispiel Gleis-tröge/Mistler) Am besten bestimmt man ein äquivalentes Kraftspektrum zu jedem Messort und jedem Messzug (Beispiel Feste Fahrbahn/Gardelegen/Auersch)
6. Prinzipiell gibt es nicht die Einfügedämmung einer Maßnahme. Die Einfügedämmung ist immer boden- und referenzsystemabhängig. Die „beste“ Einfügungsdämmung erhält man mit einem steifen Untergrund (Beispiel Unterschottermatte/Tunnel/München Gasteig/Wettschureck) Das heißt aber nicht, dass die Maßnahme durch einen künstlich versteiften Untergrund besser wird (Beispiel Unterschottermatten/RRT2006/Auersch)
Es werden Messbeispiele gezeigt, die alle neben einer hochfrequenten dynamischen Minderung auch eine mittelfrequente quasi-statische Minderung aufweisen. Dabei wird der mittelfrequente Zerstreuanteil der statischen Achslastimpulse durch die breitere Lastverteilung und damit die Impulsdehnung der Achslastimpulse reduziert. Diese Impulsdehnung lässt sich mit dem 2-dimensionalen Gleismodell berechnen. Die Minderungswirkung hängt aber wiederum vom Referenzsystem und dessen unregel¬mäßiger Steifigkeitsverteilung ab. Je unregelmäßiger der Boden und Gleisuntergrund des Referenz¬systems, desto stärker ist die Minderungswirkung.
The Federal Institute of Material Research and Testing has performed many impact tests from very small laboratory tests to very big “free-field” tests with heavy containers on stiff foundations. The first measurements have been done on a big foundation where it should be guaranteed that the foundation is rigid and the container is tested properly. Later on, a smaller drop test facility has been built on the ground inside an existing building. It had to be controlled by prediction and measurements that the drop test will not damage the building. Tests from different heights on soft, medium, and stiff targets have been done to find out rules which allow to identify acceptable and unacceptable drop tests. Later on, the biggest drop test facility has been built for masses up to 200 t. It was necessary for the design of the foundation to estimate the forces which oc-cur during the drop tests. In addititon, the acceptable tests should be selected and controlled by measurements where the impact duration is important. Dif-ferent sensors, accelerometers, accelerometers with mechanical filters, geo-phones (velocity transducers), strain gauges, and pressure cells have been ap-plied for these tasks. Signal transformations and model calculations have been used to check and understand the dynamic measurements. The simplest law is the conservation of the momentum which is a good approximation if the impact is short. If the soil under the foundation has an influence on the deceleration of the container, the maximum foundation velocity is lower than the simple esti-mation.
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.
A significant number of new wind farms has to be installed and, at the same time, existing wind farms reaching the end of their planned life need to be reused efficiently to ensure that the ambitous goals for deploying offshore wind are met. Some relevant reuse alternatives for offshore wind farms are lifetime extension, repowering utilizing existing substructures and full replacement. In this presentation - starting from experience gained from extending the lifetime of the of the U1 metro viaduct in Berlin - we discuss end-of-life decision making in offshore wind. We focus particularly on issues concerning substructures and highlight existing challenges and opprtunities in research and development.
Monopile-Gründungen sind die mit Abstand am häufigsten verwendete Gründungskonstruktion für Offshore-Windenergieanlagen. Ein wesentliches Problem bei der Bemessung ist das lokale Beulen des Gründungspfahls, welches typischerweise im Bereich der Bettung auftritt. Aufgrund der Nichtlinearität der Bettungsrandbedingung sind klassische Bemessungsansätze nicht anwendbar, so dass der Bemessungsingenieur auf eine vollständig numerische Berechnung zurückgreifen muss. In diesem Vortrag wird eine experimentelle Versuchskampagne zur Erzeugung von Kalibrierungsdaten für solche numerischen Modelle vorgestellt. Eine ausführlichere Darstellung findet sich im gleichnamigen Artikel.
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.
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.
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.
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.
One crucial metric of interest to wind farm operators is the remaining useful life (RUL) of single components, wind turbines, or even entire wind farms. Occasionally, questions arise regarding how to operate a turbine, even in the presence of manufacturing or design errors, which from a computational design standpoint reduce the remaining lifetime below the intended service life. A typical measure involves adapting the monitoring and inspection plan. Using such a maintenance plan, the author intends to simulate the lifetime of jacket-type structure in a fatigue test. The objective of the experiment is to demostrate that systems like three-dimensional jackets possess redundancies that enable reliable continued operation, despite the reduced fatigue life of individual components due to technical flaws, if an appropriate maintenance concept is in place. This presentation discusses the steps leading to the procedure of the experiment including the design process and the maintenance planning.
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.
As many wind turbines approach the end of their design lifetime, from a technical point of view, comprehensive fatigue analysis of all critical parts is necessary to decide what comes after – continued operation, repowering, or decommissioning. Typically, it is a two-stage evaluation process consisting of a physical inspection of the structure and an analytical part to compare the design and actually experienced loading conditions. Structural health monitoring helps to reduce the uncertainties in the estimations by providing insight into deviations between the designed and the built structure. Furthermore, it allows the evaluation of the consumed fatigue lifetime by analyzing the strain measurements that mirror the actual structural response to experienced environmental and operational conditions. However, the measurement values are limited to a sparse number of instrumented spots on the structure, and further extrapolation to the non-instrumented (critical) sections is required to perform a complete fatigue assessment. One known approach is the external force reconstruction, which has only scarcely been considered for application in offshore wind turbines. In order to extend the previously developed thrust force reconstruction framework, this work discusses the possibilities and challenges of wind and wave loading reconstruction in offshore wind turbine support structures.
Wir zeigen, dass bei homogenen ausgeprägt sandartigen Böden mit statistisch ermittelten Korrelationen die dynamischen Bodensteifigkeiten mit einer Genauigkeit abgeschätzt werden können, die mit der Ungenauigkeit der seismischen Verfahren übereinstimmt. Mit zunehmenden Feinkornanteil werden die Unsicherheiten der statistischen Korrelationen größer. Bei stark überkonsolidierten glazialen Böden sollte von der Anwendung empirischer Korrelationen Abstand genommen werden.