Fatigue behaviour of submerged axially loaded grouted connections

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Autoren

  • Alexander Raba

Organisationseinheiten

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Details

Titel in ÜbersetzungErmüdungsverhalten unter Wasser liegender axial beanspruchter Grout-Verbindungen
OriginalspracheEnglisch
QualifikationDoktor der Ingenieurwissenschaften
Gradverleihende Hochschule
Betreut von
  • Peter Schaumann, Betreuer*in
Datum der Verleihung des Grades13 Juli 2018
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 2018

Abstract

Die Umgestaltung der deutschen Energieversorgung zu vorwiegender Nutzung erneuerbarer Energiequellen erhöht den Bedarf an Offshore Wind Parks. Zur Installation von Windenergieanlagen in der deutschen Nordsee können aufgelöste Gründungsstrukturen verwendet werden. Diese Strukturen werden üblicherweise über Grout-Verbindungen mit ihren Gründungspfählen verbunden. Die Verbindung besteht dabei aus zwei ineinandergesteckten Rohren. Die Stahloberflächen im resultierenden Spalt werden mit Schubrippen ausgestattet und der Spalt wird mit Mörtel (Grout) gefüllt. Die Verbindung befindet sich auf Höhe des Meeresbodens und wird ohne Abdichtung gegen Wasser ausgeführt. Aufgrund des Tragverhaltens der Gründungsstruktur übertragen diese Verbindungen vorwiegend axiale Lasten. Alle derzeit verfügbaren Bemessungsverfahren für den Grenzzustand der Ermüdung dieser Ver-bindungen basieren auf in trockener Umgebung durchgeführten Versuchen. Unter Wasser ausgeführte Versuche zum Ermüdungsverhalten von Betonproben zeigen einen deutlich reduzierten Ermüdungswiderstand aufgrund zusätzlicher vom Wasser erzeugter Degradationsphänomene. Ähnliche Schadensmechanismen wurden ebenfalls an den Fundamenten von Onshore Windenergieanlagen festgestellt. Im Rahmen dieser Dissertation wird der Einfluss von Wasser auf das Ermüdungsverhalten von axial beanspruchten Grout-Verbindungen untersucht und ein Numerik basiertes Bemessungsverfahren für Ermüdungsbeanspruchung unter Wasser erarbeitet. Im ersten Schritt wurde ein Versuchsprogramm für kleinskalige Verbindungen in trockener und nasser Umgebung umgesetzt. Zusätzlich wurde der Einfluss von Spaltdicke, Grout-Material, Lastniveau und verschiedenen Belastungsfrequenzen untersucht. Insgesamt wurden 78 Ver-suchskörper ausgewertet. Die Ergebnisse zeigten eine signifikante Reduktion des Ermüdungswiderstands, bedingt durch Wechselwirkungen zwischen Verbindung und umgebendem Wasser. Im zweiten Schritt wurden großskalige Ermüdungsversuche in nasser Umgebung realisiert. Es wurden Ergebnisse an 4 Versuchskörpern mit unterschiedlichen Spaltdicken und zwei Grout-Materialien sowie unter alternierenden und Druckschwelllasten erzielt und ausgewertet. Die Gegenüberstellung dieser Ergebnisse mit vergleichbaren publizierten Versuchen in trockener Umgebung bestätigte den zuvor beobachteten Wassereinfluss für großskalige Verbindungen. In einem dritten Schritt wurden die Versuche durch numerische Simulationen ergänzt. Ein detaillierter Modellierungsansatz mit diskreten Schubrippen wurde beschrieben. Dabei kam ein nichtlineares Materialgesetz mit Zugentfestigung für die Grout-Schicht zum Einsatz. Darüber hinaus wurde ein Bemessungsverfahren für den Grenzzustand der Ermüdung unter Verwendung existierender Ermüdungskurven für Beton vorgestellt. Die Simulationen zeigten gute Übereinstimmung mit den Versuchsergebnissen. Zusammengefasst konnte eine signifikante Reduktion des Ermüdungswiderstands von axial beanspruchten Grout-Verbindungen aufgrund von Wechselwirkungen mit Wasser nachgewiesen und die maßgebenden Einflussparameter bestimmt werden. Zusätzlich wurde ein numerisches Verfahren zur Bemessung von Grout-Verbindungen für den Einsatz unter Wasser vorgestellt.

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Fatigue behaviour of submerged axially loaded grouted connections. / Raba, Alexander.
Hannover, 2018. 248 S.

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Raba, A 2018, 'Fatigue behaviour of submerged axially loaded grouted connections', Doktor der Ingenieurwissenschaften, Gottfried Wilhelm Leibniz Universität Hannover, Hannover. https://doi.org/10.15488/3668
Raba, A. (2018). Fatigue behaviour of submerged axially loaded grouted connections. [Dissertation, Gottfried Wilhelm Leibniz Universität Hannover]. https://doi.org/10.15488/3668
Raba A. Fatigue behaviour of submerged axially loaded grouted connections. Hannover, 2018. 248 S. doi: 10.15488/3668
Raba, Alexander. / Fatigue behaviour of submerged axially loaded grouted connections. Hannover, 2018. 248 S.
Download
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title = "Fatigue behaviour of submerged axially loaded grouted connections",
abstract = "With conversion of the German supply system for electrical energy towards renewable resources, the demand for offshore wind farms significantly increases. For installation of wind turbines in the German North Sea, lattice substructures such as jackets are a possible design choice. These structures are usually fixed to their steel foundation piles via grouted connections, a structural detail consisting of one steel tube inserted into a second steel tube with larger diameter. The steel surfaces located inside the resulting annulus are equipped with shear keys and the annulus is filled with a grout material. The connection is located at mudline level in submerged conditions and is manufactured without sealing against water ingress. Due to the load bearing behaviour of the substructure, these grouted connections are predominantly axially loaded. All currently available design approaches for the Fatigue Limit State of grouted connections are based on experimental tests which were carried out in dry ambient conditions. However, experimental investigations on the fatigue behaviour of concrete specimens in submerged conditions show an obvious reduction of fatigue capacity caused by interactions between specimens and the surrounding water. Corresponding degradation phenomena were also observed at foundations of onshore wind turbines. Objective of this thesis is to investigate the influence of water on the fatigue behaviour of predominantly axially loaded grouted connections. In a first step, a set-up of tests on small-scale grouted connections in both, dry and wet ambient conditions, was realised. Besides the ambient condition, the influences of different grout layer thicknesses, different grout materials, the loading level as well as varied loading frequencies were investigated. In total, results from 78 small-scale specimens were evaluated. The tests showed a significant reduction of fatigue capacity caused by the interaction between connection and sur-rounding water. This effect was also influenced by the loading frequency. In order to reassess these results for larger grouted connections, in a second step a test set-up of large-scale specimens for fatigue tests in submerged conditions was developed and implemented. The results of 4 large-scale specimens with two different grout layer thicknesses, two comparable grout materials as well as alternating and compression-compression loading were evaluated. Via comparison of the results to published experiments of comparable specimens tested in dry ambient conditions, the previously observed influence of water was confirmed for the larger scale. In a third step, the experimental results were supplemented by numerical investigations. A modelling approach including detailed models with discrete shear keys was implemented. For the grout layer a non-linear material model, capable of tensile cracking by means of large plastic strains, was used. Furthermore, a fatigue design verification approach based on existing S-N curves for concrete was developed. The obtained results showed good agreement with the experiments. In summary, a significant reduction of the fatigue capacity of axially loaded grouted connections caused by interaction with surrounding water was ascertained and the relevant parameters were identified. In addition, a numerical fatigue verification approach for the design of reliable grouted connections for application in submerged conditions was introduced.",
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Download

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N2 - With conversion of the German supply system for electrical energy towards renewable resources, the demand for offshore wind farms significantly increases. For installation of wind turbines in the German North Sea, lattice substructures such as jackets are a possible design choice. These structures are usually fixed to their steel foundation piles via grouted connections, a structural detail consisting of one steel tube inserted into a second steel tube with larger diameter. The steel surfaces located inside the resulting annulus are equipped with shear keys and the annulus is filled with a grout material. The connection is located at mudline level in submerged conditions and is manufactured without sealing against water ingress. Due to the load bearing behaviour of the substructure, these grouted connections are predominantly axially loaded. All currently available design approaches for the Fatigue Limit State of grouted connections are based on experimental tests which were carried out in dry ambient conditions. However, experimental investigations on the fatigue behaviour of concrete specimens in submerged conditions show an obvious reduction of fatigue capacity caused by interactions between specimens and the surrounding water. Corresponding degradation phenomena were also observed at foundations of onshore wind turbines. Objective of this thesis is to investigate the influence of water on the fatigue behaviour of predominantly axially loaded grouted connections. In a first step, a set-up of tests on small-scale grouted connections in both, dry and wet ambient conditions, was realised. Besides the ambient condition, the influences of different grout layer thicknesses, different grout materials, the loading level as well as varied loading frequencies were investigated. In total, results from 78 small-scale specimens were evaluated. The tests showed a significant reduction of fatigue capacity caused by the interaction between connection and sur-rounding water. This effect was also influenced by the loading frequency. In order to reassess these results for larger grouted connections, in a second step a test set-up of large-scale specimens for fatigue tests in submerged conditions was developed and implemented. The results of 4 large-scale specimens with two different grout layer thicknesses, two comparable grout materials as well as alternating and compression-compression loading were evaluated. Via comparison of the results to published experiments of comparable specimens tested in dry ambient conditions, the previously observed influence of water was confirmed for the larger scale. In a third step, the experimental results were supplemented by numerical investigations. A modelling approach including detailed models with discrete shear keys was implemented. For the grout layer a non-linear material model, capable of tensile cracking by means of large plastic strains, was used. Furthermore, a fatigue design verification approach based on existing S-N curves for concrete was developed. The obtained results showed good agreement with the experiments. In summary, a significant reduction of the fatigue capacity of axially loaded grouted connections caused by interaction with surrounding water was ascertained and the relevant parameters were identified. In addition, a numerical fatigue verification approach for the design of reliable grouted connections for application in submerged conditions was introduced.

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