TY - JOUR A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Georgi, Steven A1 - Rücker, Werner ED - Triantafyllidis, T. T1 - Special issues for the coupled transient simulation of laterally loaded offshore piles and novel experimental findings T2 - Workshop Gründung von Offshore-Windenergieanlagen CY - Karlsruhe, Germany KW - Offshore pile foundation KW - Cyclic lateral load KW - Pore pressure accumulation KW - Model testing PY - 2010 SN - 0453-3267 IS - 172 SP - 117 EP - 138 CY - Karlsruhe AN - OPUS4-24496 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Baeßler, Matthias A1 - Rücker, Werner A1 - Cuéllar, Pablo A1 - Georgi, Steven A1 - Karabeliov, Krassimire T1 - Large-scale testing facility for cyclic axially loaded piles N2 - Offshore piles have to withstand predominantly cyclic axial loads when they are installed in multi-pile configurations, as in jacket foundations. The dimensions of the pile are governed by both the internal capacity and the fatigue behaviour of the steel cross-section as well as by its external capacity in the pile-soil interaction. Owing to the large numbers of piled foundations required for current and future offshore wind farms, there is an urgent need to optimize the dimensions and related costs of single piles. With regard to the pile capacity, two major topics of research are the determination of possible capacity gains due to pile ageing effects and proper consideration of cyclic degradation. In order to investigate both effects, a large-scale testing facility has been constructed at the BAM TTS site in Horstwalde near Berlin. This open-air facility allows large tubular driven piles to be loaded cyclically in both tension and compression while studying the ageing effects by introducing delays between the testing campaigns. First results already show a moderate increase in pile capacity over time. Concerning the anticipated capacity degradation of cyclically loaded piles, preliminary results show an unexpected behaviour. Additional tests are currently being conducted for further clarification. KW - Steel driven piles KW - Offshore foundations KW - Cyclic axial loading KW - Pile ageing KW - Large-scale field testing PY - 2013 U6 - https://doi.org/10.1002/stco.201310028 SN - 1867-0520 SN - 1867-0539 VL - 6 IS - 3 SP - 200 EP - 206 PB - Ernst & Sohn CY - Berlin AN - OPUS4-29535 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rücker, Werner A1 - Karabeliov, Krassimire A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Georgi, Steven T1 - Großversuche an Rammpfählen zur Ermittlung der Tragfähigkeit unter zyklischer Belastung und Standzeit N2 - Im Rahmen mehrerer vom Bundesumweltministerium geförderter Forschungsvorhaben untersucht die BAM Bundesanstalt für Materialforschung und -prüfung zusammen mit Partnern aus Industrie und Wissenschaft das Tragverhalten von zyklisch lateral und axial belasteten Rammpfählen für Offshore-Windkraftanlagen. Neben Modellversuchen im Labor werden hierbei auch Großversuche durchgeführt. In diesem Beitrag wird das neu erstellte Testfeld der BAM zur Prüfung von Pfählen in Horstwalde vorgestellt. In den laufenden Großversuchen werden Parameter wie Tragfähigkeitsminderung infolge zyklisch-axialer Lasten im Druck- und Zugbereich sowie die Zunahme von Tragfähigkeiten durch sogenannte Anwachseffekte untersucht. Bezüglich der zyklischen Belastungen werden insbesondere als unsicher anzunehmende Wertepaare in den derzeit verwendeten Interaktionsdiagrammen betrachtet, wobei hier das Hauptaugenmerk aber nicht nur auf dem Versagen des Pfahls, sondern auch auf der Ermittlung der Resttragfähigkeit nach definierten Zyklenzahlen liegt. Im Beitrag werden erste Ergebnisse zu den Anwachseffekten präsentiert und mit Ergebnissen aus der Literatur verglichen. Des Weiteren werden das Versuchsprogramm zu den zyklisch axial belasteten Pfählen vorgestellt und erste Ergebnisse gezeigt. In einem Ausblick werden weitere Ziele des Forschungsvorhabens beschrieben. Hierzu gehören die Validierung und Kalibrierung eines existierenden Modells zur Ermittlung der Tragfähigkeit unter zyklischer Belastung auf der Grundlage aktueller Messdaten am Pfahl.----------------------------------------------------------------------------------------------- Large-scale tests on driven piles for the investigation of pile capacity under cyclic loading and ageing effects. The cyclic behaviour of axially and laterally loaded piles for the foundation of offshore wind turbines is being investigated by the Federal Institute for Materials Research and Testing (BAM) in the frame of several research projects funded by the German Federal Ministry for the Environment and carried out in cooperation with industrial and academic partners. To this end, physical model tests in reduced scale as well as large scale field tests are being performed. This paper presents the new pile testing facility in the BAM's testing site at Horstwalde. The large-scale tests being performed there are aiming at the pile capacity degradation due to cyclic axial loading (both in tension and compression) as well as at the investigation of the capacity gains due to ageing effects (pile setup). Concerning the cyclic loading, the investigations have been mainly focused on special load combinations where there is little experience and where current interaction diagrams are loosely defined. However, the aim of the tests was not the cyclic failure, but rather the assessment of the post-cyclic capacity after the application of a pre-defined number of load cycles. Here, the testing program is summarised and some key results from the first testing campaign are discussed. The paper also presents some preliminary results concerning the capacity gains through ageing and compares them to previous experience from the literature. Finally, the paper gives an outlook on further goals of the current research projects, including the validation and calibration of a design model for the cyclic capacity of piles based on measured data from real piles. PY - 2013 U6 - https://doi.org/10.1002/gete.201200021 SN - 0172-6145 SN - 1865-7362 SN - 2190-6653 VL - 36 IS - 2 SP - 77 EP - 89 PB - VGE Verl. GmbH CY - Essen AN - OPUS4-29517 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Georgi, Steven A1 - Rücker, Werner T1 - Porenwasserdruckaufbau und Bodenentfestigung um Pfahlgründungen von Offshore-Windenergieanlagen N2 - Die Gründung von Offshore-Windenergieanlagen erfordert oft die Installation von Stahl-Pfählen mit großem Durchmesser, entweder als Monopile- oder Mehrpfahl-Konfiguration (Jacket, Tripod, usw.). In dieser Veröffentlichung werden die Auswirkungen einer zyklischen lateralen Belastung auf Offshore-Pfahlgründungen untersucht. Hierbei wird besonderes Augenmerk auf die Entwicklung des Porenwasserdrucks im umgebenden gesättigten Boden gelegt. Es wird gezeigt, dass der progressive Aufbau von Porenwasserdruck zu erheblichen Veränderungen des Verhaltens der Gründung unter externer Belastung führen kann, die die Stabilität bzw. Gebrauchstauglichkeit der Anlage potenziell gefährden. Dazu werden auch einige Effekte, die während eines realistischen Sturms von moderater Stärke entstehen, untersucht. Die transiente Abminderung der Gründungssteifigkeit wird hierbei thematisiert. Die genannten Aspekte wurden von den Autoren mittels eines gekoppelten zweiphasigen numerischen Modells der Offshore-Gründung untersucht. Das verwendete Stoffgesetz für den Boden, im Rahmen der Theorie der verallgemeinerten Plastizität, kann wichtige Merkmale von zyklischem Bodenverhalten reproduzieren, wie z. B. die Tendenz zu einer fortschreitenden Verdichtung unter zyklischer Belastung, die für Verflüssigungsphänomene unter undränierten Bedingungen verantwortlich ist. Die Notwendigkeit der Verwendung eines solchen Ansatzes wird hier anhand von Vergleichsberechnungen mit einem einfacheren Stoffmodell bzw. mit einem ungekoppelten Modell erörtet. Abschließend werden einige Implikationen der untersuchten Fragenstellungen für die praktische Bemessung von Offshore-Monopiles diskutiert und spezifische Empfehlungen gegeben.--------------------------------------------------------------------------------------------------------------------------- For the installation of wind turbines in the offshore environment and their foundation in the seabed it is customary to employ large-diameter steel piles, either in monopile or multi-pile configurations (jacket, tripod, etc. ...). The effects of cyclic lateral loading on the offshore piles and particularly the possibility of a progressive accumulation of residual pore water pressure within the saturated embedding soil are discussed in this article. Here it is shown that this can lead to significant changes of their behaviour under external loading, which can potentially compromise the foundation's stability or serviceability. Furthermore, some of the singular effects arising during a realistic storm of moderate magnitude as well as their potential for transient damages to the foundation's stiffness are addressed in the paper. For the investigation of these phenomena the authors have employed a coupled bi-phasic analytical model of the offshore foundation. The constitutive model employed for the seabed, in the frame of the theory of Generalized Plasticity, can reproduce some complex features of cyclic soil behaviour such as the tendency for a progressive densification under cyclic loading, which is responsible for the soil liquefaction phenomena in undrained conditions. Finally, some implications and specific recommendations for the design of offshore monopiles in the frame of the limit states are provided. KW - Porenwasserdruckaufbau KW - Offshore-Pfahlgründung KW - Belastung KW - Zyklische KW - Pore pressure build-up KW - Offshore pile foundation KW - Cyclic loading PY - 2012 U6 - https://doi.org/10.1002/bate.201200031 SN - 0932-8351 SN - 1437-0999 SN - 0005-6820 SN - 0341-1052 SN - 0932-6359 SN - 0932-8351 VL - 89 IS - 9 SP - 585 EP - 593 PB - Ernst & Sohn CY - Berlin AN - OPUS4-26981 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cuéllar, Pablo A1 - Georgi, Steven A1 - Baeßler, Matthias A1 - Rücker, Werner T1 - On the quasi-static granular convective flow and sand densification around pile foundations under cyclic lateral loading N2 - The saturated sand surrounding an offshore pile foundation under quasi-static cyclic lateral load can show the physical phenomena of macromechanical densification and convective granular flow. Based on the results from physical model tests at different geometrical scales, this paper provides a certain quantification of such phenomena and discusses their causes and consequences. The progressive sand densification leads to subsidence of the soil surface and a significant stiffening of the pile behaviour. Conversely, the ratcheting convective motion of two closed cells of soil beneath the pile-head is responsible for an endless grain migration at the soil surface, the inverse grading of the convected material and a direct shear of the sand at the distinct boundary of the revolving soil domain. In this respect, and from a macromechanical perspective considering the soil as a continuum, it appears that the convecting material tends to follow gradient lines of shear stress during its ratcheting motion. Concluding the paper, the practical relevance of these phenomena and their extrapolation to other conditions are briefly discussed. KW - Offshore pile foundation KW - Cyclic loading KW - Ratcheting KW - Granular convection KW - Densification PY - 2012 U6 - https://doi.org/10.1007/s10035-011-0305-0 SN - 1434-5021 SN - 1434-7636 VL - 14 IS - 1 SP - 11 EP - 25 PB - Springer CY - Berlin ; Heidelberg AN - OPUS4-25405 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Karabeliov, Krassimire A1 - Baeßler, Matthias A1 - Cuéllar, Pablo A1 - Rücker, Werner T1 - A method for system identification of a structure supported by nonlinear springs using evolutionary computing N2 - A mechanical structure supported by nonlinear springs subjected to an external load is considered. If all mechanical parameters of the system were known, the displacement of the system subjected to this load could be easily calculated. If not all of the parameters are known, but the load and the displacement are measured at one location, an inverse problem exists. In the presented problem the nonlinear springs are unknown and have to be determined. At first glance a problem needs to be solved, which is underdetermined due to the number of unknown variables. However, evolutionary computing can be applied to solve this inverse, nonlinear and multimodal problem. Sometimes a prior knowledge exists on certain system properties, which is difficult to implement into analytical or numerical solver. This knowledge can play a decisive role in identifying the system properties and it can be easily included as boundary condition when applying evolutionary algorithm. This article examines how and under what conditions the spring resistances can be identified. The procedure is exemplified at a mechanical system of a pile foundation. T2 - 2nd International conference on mathematical modeling in physical sciences 2013 CY - Prague, Czech Republic DA - 01.09.2013 PY - 2014 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-304531 UR - http://iopscience.iop.org/1742-6596/490/1/012095/pdf/1742-6596_490_1_012095.pdf SN - 1742-6588 SN - 1742-6596 VL - 490 IS - 012095 SP - 1 EP - 4 PB - IOP Publ. CY - Bristol, UK AN - OPUS4-30453 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cuéllar, Pablo A1 - Mira, P. A1 - Pastor, M. A1 - Merodo, J.A.F. A1 - Baeßler, Matthias A1 - Rücker, Werner T1 - A numerical model for the transient analysis of offshore foundations under cyclic loading N2 - A comprehensive numerical model for the analysis of offshore foundations under a general transient loading is presented here. The theoretical basis of the model lies on the Swansea formulation of Biot's equations of dynamic poroelasticity combined with a constitutive model that reproduces key aspects of cyclic soil behaviour in the frame of the theory of generalised plasticity. On the practical side, the adoption of appropriate finite element formulations may prevent the appearance of spurious numerical instabilities of the pore pressure field. In this respect, the use of a coupled enhanced-strain element is here proposed. On the other hand, the practicality of the presented model depends ultimately on its computational efficiency. Some practical recommendations concerning the solution strategies, the matrix storage/handling procedures and the parallel multi-processor computation are here provided. Finally, the performance of the model with a benchmark study case and its practical application to analyse the soil–structure interaction of an offshore monopile under a realistic transient storm loading are discussed. KW - Offshore foundations KW - Cyclic loading KW - Numerical model KW - Pore pressure accumulation KW - Liquefaction analysis PY - 2014 U6 - https://doi.org/10.1016/j.compgeo.2014.02.005 SN - 0266-352x VL - 59 SP - 75 EP - 86 PB - Elsevier Ltd. CY - Barking AN - OPUS4-30490 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Baeßler, Matthias A1 - Rücker, Werner A1 - Cuéllar, Pablo A1 - Georgi, Steven A1 - Karabeliov, Krassimire T1 - Großmaßstäblicher Versuchsstand für zyklisch axial belastete Pfähle N2 - Offshore-Pfähle in Mehrpfahlgründungsstrukturen wie Jacket-Gründungen müssen nach der Rammung überwiegend zyklisch axialen Belastungen widerstehen. Die Abmessungen der Pfähle werden sowohl von der inneren Tragfähigkeit und dem Ermüdungsverhalten des Stahlquerschnittes als auch von der äußeren Tragfähigkeit und der Pfahl-Boden-Interaktion bestimmt. Aufgrund der großen Zahl von Pfahlgründungen, die für aktuelle und zukünftige Windparkprojekte benötigt werden, besteht ein dringender Bedarf, die Dimensionierung und die damit verbundenen Kosten des Einzelpfahles zu optimieren. Bezüglich der Pfahltragfähigkeit sind wichtige aktuelle Forschungsthemen eine mögliche Traglaststeigerung durch Anwachsen und die geeignete Abschätzung der zyklischen Degradation. Zur Untersuchung beider Effekte wurde eine großmaßstäbliche Versuchsanlage auf dem Testgelände BAM TTS in Horstwalde nahe Berlin errichtet. Auf diesem Versuchsfeld können große Stahlrohrammpfähle zyklisch druck- und zugbelastet werden. Zudem kann die Untersuchung von Alterungseffekten durch zeitlichen Versatz zwischen den Messkampagnen untersucht werden. Erste Ergebnisse zeigen einen Anstieg der Pfahltragfähigkeit bis zu ca. 60 % nach einer Standzeit von ca. 18 Monaten. Für die Degradation der Tragfähigkeit der zyklisch belasteten Pfähle zeigen die ersten vorläufigen Ergebnisse ein zum Teil unerwartetes Verhalten. Zusätzliche Untersuchungen werden derzeit zur weiteren Abklärung durchgeführt. KW - Stahlpfahl, gerammt KW - Offshore-Gründung KW - Anwachsen KW - Feldversuch KW - Tragfähigkeit KW - Rammung KW - Offshore foundation KW - Increase KW - Field test KW - Bearing capacitiy KW - Driving Versuche - Experimental set-ups KW - Berechnungs- und Bemessungsverfahren - Analysis and calculation KW - Stahlhochbau - Steel buildings KW - Mast- und Turmbau - Masts and towers KW - Stahlwasserbau - Steel structures for hydraulic engineering KW - Steel pile, driven in PY - 2014 U6 - https://doi.org/10.1002/stab.201430005 SN - 0038-9145 SN - 1437-1049 SN - 0932-6375 VL - 83 IS - Suppl. 1 (Erneuerbare Energien) SP - 26 EP - 32 PB - Ernst CY - Berlin AN - OPUS4-30898 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Rücker, Werner T1 - Ratcheting convective cells of sand grains around offshore piles under cyclic lateral loads N2 - Sand densification around the pile has traditionally been regarded as an explanation for the grain migration and soil subsidence that often occur around cyclic laterally loaded piles embedded in sand. Supported by new empirical evidence, this paper proposes that, additionally to some soil densification around the pile, the main cause for the continuous "steady-state" grain migration is a convective cell flow of sand grains in the vicinities of the pile head. Such convective flow would be caused by a ratcheting mechanism triggered by the cyclic low-frequency lateral displacements of the pile. Furthermore, the experimental results suggest that the limit between the convective cell and the static soil is marked by a distinct direct shear surface. This might shed some light into the complex phenomena related to the pile-soil interaction in the upper layers of the bedding, which are normally the main contributor for the lateral load-bearing capacity of piles. KW - Grain migration KW - Pile foundation KW - Cyclic lateral load KW - Ratcheting KW - Convection KW - Densification PY - 2009 U6 - https://doi.org/10.1007/s10035-009-0153-3 SN - 1434-5021 SN - 1434-7636 SP - 1 EP - 12(?) PB - Springer CY - Berlin ; Heidelberg AN - OPUS4-20104 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Karabeliov, Krassimire A1 - Cuéllar, Pablo A1 - Baeßler, Matthias A1 - Rücker, Werner T1 - System identification of inverse, multimodal and nonlinear problems using evolutionary computing - Application to a pile structure supported on nonlinear springs N2 - This paper deals with the system identification of a mechanical structure supported by nonlinear springs subjected to an external load. If all mechanical parameters of the system were known, the displacement of the system subjected to this load could be easily calculated. However, the monitoring applications often deal with the inverse problem. The loads and displacements of the system are known and certain mechanical Parameters of the system are sought. The solution of such inverse problems can be difficult, especially when they have a nonlinear and multimodal character, which often makes them appear intractable at first sight. However, evolutionary computing can be applied to solve this inverse, nonlinear and multimodal problem. Sometimes a prior knowledge exists on certain system properties, which is difficult to implement into analytical or numerical solvers. This knowledge can play a decisive role in identifying the System properties and it can be easily included as a boundary condition when applying evolutionary algorithms. This article discusses how and under what conditions the unknown spring resistances can be identified. The practical application of this procedure is exemplified here with the mechanical system of a pile foundation. KW - Evolutionary computing KW - Inverse problem KW - Multimodal solution KW - System identification KW - Pile monitoring PY - 2015 U6 - https://doi.org/10.1016/j.engstruct.2015.07.034 SN - 0141-0296 SN - 1873-7323 VL - 101 SP - 609 EP - 620 AN - OPUS4-39310 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -