Axially loaded grouted connections in offshore conditions using ordinary portland cement

[EN] A grouted connection (GC) is a hybrid connection which joins two telescoped steel tubes by filling the annulus between the steel tubes with grout. GCs are frequently used to enable a force fitted connection between piles and substructure of offshore wind turbines. At latticed substructures this connection is located at mudline level in wet ambient conditions (AC). Nowadays special grout materials are used to achieve not only best mechanical properties but also a good performance during grouting in offshore conditions.To reduce production costs the use of ordinary portland cement (OPC) is investigated as an alternative filling material within this paper. OPC has a much lower tendency to segregate, as there are no aggregates added. This leads to more simplified, stable and cheaper production processes offshore. Further focus is put on the failure mode of OPC filled GCs in submerged condtions.For an appropriate use of OPC offshore a feasible mechanical performance needs to be ensured. Investigating this, small and large-scale laboratory tests were performed at Leibniz Universität Hannover. Using the experimental test setup of previous investigations for special high performance grouts (HPG) [1, 2], enables a direct comparison of HPG and OPC. Documenting liquid and solid OPC properties, like slump flow and compressive strength confirms a stable material quality. Small-scale ULS-tests showed significantly lower ULS-capacities and a more brittle failing process compared to HPG. Lagre-scale tests confirmed the observed failure mechanisms of Schaumann and Raba for OPC filled GCs in submerged conditions [3]. Carried out tests showed significant influence of grout material and confirmed influence of grout annulus size on fatigue capacity.The presented results were achieved within the research project ‘GROWup - Grouted Joints for Offshore Wind Energy Converters under reversed axial loadings and upscaled thicknesses’ funded by the German Federal Ministry for Economic Affairs and Energy (BMWi, funding sign: 0325290). The research partners were Institute for Steel Construction and Institute of Buildung Material Science, both at Leibniz Universität Hannover, Germany. The authors thank the BMWi for funding and all accompanying industry project partners (DNV GL, Senvion SE, Siemens Wind Power, Wilke & Schiele Consulting GmbH) for their support. Additionally the authors thank the material manufacturers for their support. Concluding thanks goes to Prof. Lohaus and his team from the Institute of Building Material Science for an excellent project collaboration.Schaumann, P.; Henneberg, J.; Raba, A. (2018). Axially loaded grouted connections in offshore conditions using ordinary portland cement. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 541-547. https://doi.org/10.4995/ASCCS2018.2018.6944OCS54154

Ermüdungsverhalten unter Wasser liegender axial beanspruchter Grout-Verbindungen

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.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

Characterization of the Pseudomonas aeruginosa NQR Complex, a Novel Form of Bacterial Proton Pump, and the Ubiquinone Binding Site

The proton/sodium pumping NADH:Ubiquinone oxidoreductase enzyme complex (NQR) plays a key role in the energy metabolism of a diverse range of bacteria, including pathogenic species such as Vibrio cholera, Pseudomonas aeruginosa, Chlamydia trachomatis, as well as others. Residing in the cytoplasmic membrane of these bacteria, the enzyme couples the transfer of electrons to the pumping of cations across the cell membrane. In all previously studied homologues, the enzyme generates a sodium gradient through its pumping activity that can be utilized by the cell to power essential homeostatic processes. Furthermore, the electrochemical gradient generated by this enzyme has been shown to regulate the production of virulent factors and the efficacy of antibiotic extrusion and elimination. Although certain homologues have been investigated, particularly that of V. cholerae (Vc-NQR), the NQR homologues belonging to important pathogenic species have not been well studied. In the research detailed in this thesis, the first characterization of the NQR of P. aeruginosa (Pa-NQR) is described which identified this homologue as a new form of bacterial proton pump, differentiating it from all other studied homologues of NQR. Additionally, as part of this study our research group characterized the mechanism of inhibition of Pa-NQR by the molecule HQNO which is produced by P. aeruginosa and is known to be a strong inhibitor of Vc-NQR. Our results show that Pa-NQR possesses resistance to inhibition by this molecule compared to Vc-NQR, pinpointing residue F155 of subunit D as being important to resistance and the type of inhibition to be partial-mixed. Moreover, in further developing the understanding of the NQR of V. cholerae, we investigated the binding site of ubiquinone, the final electron acceptor of NQR’s electron transfer process, determining residues P185, L190, and F193 to be important for maintaining the structural composition of the ubiquinone pocket, ensuring efficient substrate binding and catalysis

Characterization of the Pseudomonas aeruginosa NQR Complex, a Novel Form of Bacterial Proton Pump, and the Ubiquinone Binding Site

The proton/sodium pumping NADH:Ubiquinone oxidoreductase enzyme complex (NQR) plays a key role in the energy metabolism of a diverse range of bacteria, including pathogenic species such as Vibrio cholera, Pseudomonas aeruginosa, Chlamydia trachomatis, as well as others. Residing in the cytoplasmic membrane of these bacteria, the enzyme couples the transfer of electrons to the pumping of cations across the cell membrane. In all previously studied homologues, the enzyme generates a sodium gradient through its pumping activity that can be utilized by the cell to power essential homeostatic processes. Furthermore, the electrochemical gradient generated by this enzyme has been shown to regulate the production of virulent factors and the efficacy of antibiotic extrusion and elimination. Although certain homologues have been investigated, particularly that of V. cholerae (Vc-NQR), the NQR homologues belonging to important pathogenic species have not been well studied. In the research detailed in this thesis, the first characterization of the NQR of P. aeruginosa (Pa-NQR) is described which identified this homologue as a new form of bacterial proton pump, differentiating it from all other studied homologues of NQR. Additionally, as part of this study our research group characterized the mechanism of inhibition of Pa-NQR by the molecule HQNO which is produced by P. aeruginosa and is known to be a strong inhibitor of Vc-NQR. Our results show that Pa-NQR possesses resistance to inhibition by this molecule compared to Vc-NQR, pinpointing residue F155 of subunit D as being important to resistance and the type of inhibition to be partial-mixed. Moreover, in further developing the understanding of the NQR of V. cholerae, we investigated the binding site of ubiquinone, the final electron acceptor of NQR’s electron transfer process, determining residues P185, L190, and F193 to be important for maintaining the structural composition of the ubiquinone pocket, ensuring efficient substrate binding and catalysis

Fatigue behaviour of grouted connections at different ambient conditions and loading scenarios

Grouted connections are frequently used as structural detail of offshore wind turbines and platforms for the load transferring connection between piles and support structure. At latticed substructures this connection is commonly located at mudline. However, a potential influence of the surrounding water on the connection's fatigue behaviour was neglected in earlier tests and consequential design methods. Herein described experimental investigations at small and large-scale fatigue tests in submerged conditions showed a significant reduction of endurable load cycles. In addition, the water impact caused varied damage mechanism in the connection. © 2017 The Author(s)

Kinetic characterization of Vibrio cholerae ApbE: Substrate specificity and regulatory mechanisms.

ApbE is a member of a novel family of flavin transferases that incorporates flavin mononucleotide (FMN) to subunits of diverse respiratory complexes, which fulfill important homeostatic functions. In this work a detailed characterization of Vibrio cholerae ApbE physiologic activity, substrate specificity and pH dependency was carried out. The data obtained show novel characteristics of the regulation and function of this family. For instance, our experiments indicate that divalent cations are essential for ApbE function, and that the selectivity depends largely on size and the coordination sphere of the cation. Our data also show that ApbE regulation by pH, ADP and potassium is an important mechanism that enhances the adaptation, survival and colonization of V. cholerae in the small intestine. Moreover, studies of the pH-dependency of the activity show that the reaction is favored under alkaline conditions, with a pKa of 8.4. These studies, together with sequence and structure analysis allowed us to identify His257, which is absolutely conserved in the family, as a candidate for the residue whose deprotonation controls the activity. Remarkably, the mutant H257G abolished the flavin transfer activity, strongly indicating that this residue plays an important role in the catalytic mechanism of ApbE

Substrate titration of ApbE.

<p>A and B) FAD and NqrC titrations on the steady state activity of ApbE, respectively. The titrations were performed by varying the concentration of one substrate at a fixed concentration of the other (FAD 1 mM, NqrC 100 μM). Inset shows the double reciprocal plots. The kinetic parameters were obtained by fitting the data to the Michaelis-Menten equation.</p

Kinetic parameters of <i>V</i>. <i>cholerae</i> ApbE.

<p>Kinetic parameters of <i>V</i>. <i>cholerae</i> ApbE.</p