7.2 Ingenieurbau
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- Pile foundations (6)
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- 7.2 Ingenieurbau (170) (entfernen)
Due to the many possible applications, the uncomplicated production and the high application range, reinforced concrete is a widely used building material. This large range of physical material properties still poses an engineering challenge in determining all necessary requirements for predicting dynamic effects under impact load.
Many aspects of impact have already been examined and some correlations have been studied intensively. Examples are the work of Lastunen and Booker, who studied the influence of projectile properties on the impact form. Li has also investigated the local effects of an impact. The field of detailed damage analysis has not been in focus so far.
This presentation shows some studies in medium-velocity impact with the focus on post-impact damage evaluation. The impactor is modified so that the test plates show low penetration on the top and scabbing on the bottom. With the unique tomography lab test stand at BAM the plate is scanned after the impact and the damage is analyzed. Cracks and scabbing are made visible with a reconstruction. The comparison of simulation and tomography allows to create prognosis models for damage characterization.
This presentation deals with the phenomenology and design of pile foundations for offshore wind turbines, and is divided in 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.
The second lecture continues with the case of lateraly 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 cyclic pile fatigue and the so-called pile setup (i.e. the time effects on the axial pile capacity). The relevance of these two topics is illustrated with experimental results from a field testing campaign on real large-scale piles.
Remediation of Cracks Formed in Grouted Connections of Offshore Energy Structures under Static Loads
(2018)
The future energy demand necessitates the exploration of all potential energy sources both onshore and offshore. Global trend has shifted towards offshore energy, which can be obtained from either carbon intensive or renewable options, hence requiring structures such as rigs, platforms, and monopiles. Most of these structures adopt easily installable construction techniques, where lower foundation need to be connected with the super structure by mean of grouted composite joints. Generally, these composite connections have exterior sleeve, interior pile and infill grout. Being located in remote offshore conditions, connections can experience considerable adverse loading during their lifetimes. Degradations were reported inside similar connections, which were installed in last three decades. Besides, grouting in the offshore sites may often be proven difficult, which eventually leads to reduced capacity of connections in the long run. Thus, repair and rehabilitation of such connections should be planned ahead to minimize operational delays and costs in the future. This study aims at characterizing the nature of crack generation in grouted connections and thereby identifying the potential of repair using suitable repair material. Scaled grouted joints were manufactured using a novel mold, and connections were loaded under static load to visualize the main failure pattern. The failure mechanism and loading capacity are found compatible to previous results from earlier literature. Grouted connection was then repaired using cementitious injectable grout. The effectiveness of the repair system is also discussed.
Design challenges for offshore wind-farms. From foundation mechanics to wind-farm aerodynamics
(2018)
This talk provides a brief introduction on general engineering aspects of offshore wind energy production. Then some geomechanical issues for the foundation of OWTs into the seabed are introduced, while the results from experimental investigations and coupled computational analysis are discussed.
In the second part of the seminar, 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.
Concerning the geomechanical issues the talk shows that: i) The pile’s bearing capacity can degrade under cyclic loading (waves, wind, …). ii) The time effects can be relevant: Capacity improvement can be substantial, but also fragile. iii) There are cyclic PWP effects: Cyclic interaction with pore water may lead to soil softening and an uncoupled analysis (current design practice) is potentially unsafe.
And concerning the hydromechanical and aerodynamical design considerations, this seminar shows that: i) Numerical analysis of turbine’s interaction with wind/waves is useful and affordable. ii) Simplified models can provide insight into windfarm aerodynamics. iii) Turbulent wake analysis is very relevant for the windfarm layout.
Die Grundidee einer Schwingungsminderung ist es eine tiefe Eigenfrequenz der Struktur zu erreichen, so dass höhere Frequenzen abgemindert werden. Das gilt für die Minderung an der Quelle, zum Beispiel einem Eisenbahngleis, und für die Minderung am Empfänger, dem Gebäude. Die Eigenfrequenz ermittelt man aus dem Verhältnis der Auflagersteifigkeit und der Masse. Wie ist die Masse bei einem Gebäude zu wählen? Und wie ist die Untergrund-steifigkeit zu berücksichtigen? Als Referenzsituation ohne Minderungsma߬nahme? Der Beitrag bringt Rechenergebnisse zu abgefederten Gebäuden mit einfachen und komplexen (FE-) Modellen, Mess- und Rechenergebnisse zur Schwingungsübertragung von unabge-federten Gebäuden. Es wird der Einfluss der Abstimmfrequenz, der Bodensteifigkeit und der „starren“ Gebäudemasse untersucht. Die komplexen Gebäudemodelle erlauben, neben der Berechnung einer elastischen Gebäudelagerung, auch die Variation von Gebäudepara¬metern zur Reduktion der Deckenschwingungen. Den Ergebnissen bei der Erschütterungs-übertragung in Gebäude werden zwei ähnliche Beispiele zur elastischen Maschinenlagerung und zur elastischen Gleislagerung gegenübergestellt.
Explosion-induced ground vibrations have been measured at several places. Results about the wave propagation are shown in this contribution. The particle velocities of the soil have been measured at up to 1000 m distance from the explosion and are presented as time records (seismograms) and one-third octave band spectra (transfer functions). The results are compared with the results of hammer impacts. The seismograms clearly show different wave types, compressional waves of the air, the water and the soil, and the Rayleigh wave. The hammer impacts yield good results up to 100 m and incorporate higher frequencies at about 50 Hz, whereas the explosion results in a ground vibration with frequencies around 10 Hz and a longer range of influence. Explosion and hammer excitations are evaluated for the wave velocities of the soil by using the wavenumber and the spatial auto-correlation method. The attenuation of the ground vibration amplitudes A with distance r can well be presented by a power law A ~ r -q. This type of amplitude-distance law and the corresponding power q > 1 are substantiated in the contribution. The influence of the charge weight W is evaluated as an additional power law A ~ W -p for each measuring site. The power is found quite similarly around q 0.6 as all sites have a medium soft soil such as sand and clay. The obtained amplitude-charge-distance law can be used to predict the explosion-induced ground and building vibrations at other sites.
Use of DEM-LBM modeling to prove the relevance of free jet model for soil erosion by impinging jet
(2018)
The aim of this study is to provide a micromechanical insight into the mechanisms taking place during the erosion of a cohesive granular material driven by a fluid flow, the objectives are summarized as follows:
Perform numerical erosion tests.
Parallelization of the code (Gpu).
Extensive parametric analysis => rely micro parameters (eg. Cohesion) to macro parameters (eg. Soil erodibility, mechanical strengths).
This presentation deals with the phenomenology and design of pile foundations for offshore wind turbines, and is divided in 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.
The second lecture continues with the case of lateraly 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 cyclic pile fatigue and the so-called pile setup (i.e. the time effects on the axial pile capacity). The relevance of these two topics is illustrated with experimental results from a field testing campaign on real large-scale piles.