Fatigue assessment of large-size bolting assemblies for wind turbine support structures

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Autoren

  • Rasmus Eichstädt

Organisationseinheiten

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Details

Titel in ÜbersetzungErmüdungsbewertung sehr großer Schraubenverbindungen für Tragstrukturen von Windenergieanlagen
OriginalspracheEnglisch
QualifikationDoktor der Ingenieurwissenschaften
Gradverleihende Hochschule
Betreut von
  • Peter Schaumann, Betreuer*in
Datum der Verleihung des Grades28 Juni 2019
ErscheinungsortHannover
PublikationsstatusVeröffentlicht - 2019

Abstract

Hochfeste Schraubengarnituren des Systems HV mit Durchmessern M36 und größer kommen bevorzugt in Ringflanschverbindungen von Tragstrukturen von Windenergieanlagen zum Einsatz. Insbesondere an unteren Turmsektionen wird bedingt durch die auftretenden Belastungen häufig die Verwendung sehr großer Durchmesser M64 oder M72 erforderlich. Die HV-Schrauben sind hohen zyklischen Lasten mit variablen Amplituden ausgesetzt. Zur Begrenzung von Ermüdungsbeanspruchung werden die Schrauben daher auf hohe Vorspannungsniveaus angezogen. Ein zuverlässiger Schutz gegen Korrosion wird in der Regel durch Feuerverzinken sichergestellt. Es ist bekannt, dass die dabei thermisch hergestellte Zinkoberfläche die zyklische Beanspruchbarkeit stählerner Bauteile beeinträchtigt. Zudem hat auch das durch die Vorspannung erzeugte hohe Mittelspannungsniveau einen Einfluss auf die Ermüdungseigenschaften der Schrauben. Die Durchführung von Ermüdungsversuchen an großen HV-Garnituren, insbesondere unter repräsentativer Mittelspannung, ist mit hohen Anforderungen an die verwendete Prüfeinrichtung verbunden. Bemessungswöhlerlinien normativer Regelwerke, mit besonderer praktischer Relevanz der EN 1993-1-9, sind aus diesem Grund nur begrenzt für große Schraubendurchmesser validiert. Zudem ist der quantitative Einfluss der Feuerverzinkung auf die Ermüdungsfestigkeit hochfester großer Schrauben bislang nicht abschließend untersucht. Ergänzend zu kostspieligen Ermüdungsversuchen können mit analytischen Methoden spezifische ermüdungsrelevante Einflussfaktoren isoliert bewertet werden. Allerdings sind hierzu geeignete Verfahren noch für die Anwendung auf große HV-Garnituren anzupassen und zu validieren. Außerdem bedarf es einer geeigneten Möglichkeit zur Berücksichtigung des Einflusses der Feuerverzinkung. Diese Dissertation beinhaltet umfangreiche, systematische Untersuchungen zum Ermüdungsverhalten großer HV-Schraubengarnituren mit experimentellen und analytischen Methoden. Die durchgeführten Ermüdungsversuche erweitern die experimentelle Validierung normativer Regelwerke erstmalig bis zum Nenndurchmesser M64. Die Anwendbarkeit des relevanten Kerbfalls 50 aus dem Eurocode 3 kann dabei bestätigt werden. Der Vergleich der erzielten Versuchsergebnisse an feuerverzinkten HV-Garnituren mit Durchmessern M36 und M64 sowie weiterführende analytische Untersuchungen zeigen für diese Schraubengrößen einen geringen Einfluss des Durchmessers. Die im Eurocode 3 berücksichtigte durchmesserabhängige Reduzierung führt darum tendenziell zu einer Unterschätzung der Ermüdungsfestigkeit. Versuche mit variablen Amplituden deuten darüber hinaus darauf hin, dass die verwendete Hypothese zur Schädigungsakkumulation zu einer konservativen Bemessung führt. Bezüglich des Unterschieds der Ermüdungsfestigkeit bei unbeschichteten und feuerverzinkten Garnituren weisen die Versuche an M36 und M64 Schrauben uneinheitliche Ergebnisse auf, was eine mögliche Besserstellung schwarzer Schrauben in Frage stellt. Das für die Anwendung auf große HV-Schrauben weiterentwickelte analytische Bewertungsverfahren der Ermüdungsfestigkeit liefert Ergebnisse in guter Näherung mit Versuchen unterschiedlicher Durchmesser und Lastverhältnisse. Ein vorgeschlagenes Ingenieurmodell ermöglicht dabei ebenfalls die Ermüdungsberechnung feuerverzinkter Schrauben.

Zitieren

Fatigue assessment of large-size bolting assemblies for wind turbine support structures. / Eichstädt, Rasmus.
Hannover, 2019. 214 S.

Publikation: Qualifikations-/Studienabschlussarbeit › Dissertation

Eichstädt, R 2019, 'Fatigue assessment of large-size bolting assemblies for wind turbine support structures', Doktor der Ingenieurwissenschaften, Gottfried Wilhelm Leibniz Universität Hannover, Hannover. https://doi.org/10.15488/5157
Eichstädt, R. (2019). Fatigue assessment of large-size bolting assemblies for wind turbine support structures. [Dissertation, Gottfried Wilhelm Leibniz Universität Hannover]. https://doi.org/10.15488/5157
Eichstädt R. Fatigue assessment of large-size bolting assemblies for wind turbine support structures. Hannover, 2019. 214 S. doi: 10.15488/5157
Download
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title = "Fatigue assessment of large-size bolting assemblies for wind turbine support structures",
abstract = "High-strength {\textquoteleft}System HV{\textquoteright} bolting assemblies with large bolt diameters of M36 and bigger are frequently used in ring-flange connections in steel support structures for on- and offshore wind turbines. At the bottom parts of the supporting steel towers the magnitude of the acting loads usually requires the application of very large bolt diameters M64 or M72. The bolts are subjected to high cyclic loads with considerable numbers of load cycles and variable amplitudes. Thus, for reduction of fatigue loads, preloading of bolts with high forces is mandatory. Reliable protection against corrosion is commonly achieved by hot-dip galvanizing. It is known that the zinc coating has an impact on the fatigue strength of structural steel components. Moreover, the high mean stress level affects the bolts{\textquoteright} fatigue behaviour and thus needs to be appropriately considered in experimental as well as analytical fatigue analyses. Fatigue testing of HV-bolts with large diameters under a representative mean stress level imposes challenges to the required testing equipment. Hence, S-N curves in applicable design standards, in particular EN 1993-1-9, are mostly validated on tests with smaller bolts and the influence of an increased diameter is yet to be verified. Moreover, the quantitative effect of hot-dip galvanizing on the fatigue strength of large-size HV-bolts is still under investigation. Analytical fatigue assessment procedures provide valuable potentials to supplement expensive experimental test series and to discretely investigate specific impact factors with relevance to the fatigue strength. However, to this end suitable assessment methodologies need to be adapted and validated for the application to HV-bolts with large diameters as well as for an appropriate consideration of the effect of hot-dip galvanizing. This dissertation presents comprehensive research work on the experimental and analytical fatigue assessment of large-size HV-bolts. The performed fatigue tests extend the range of the experimental validation of normative regulations to a bolt diameter of M64, representative for the upper end of bolt sizes applied in today{\textquoteright}s modern wind turbine support structures. Thereby, the safe applicability of the relevant fatigue class FAT 50 of the Eurocode 3 is confirmed. The comparison of performed tests on hot-dip galvanized bolts of diameters M36 and M64, as well as further analytical analyses, indicate a minor impact of the bolt size in the considered large diameter range. The corresponding reduction function of the Eurocode 3 thus tends to overestimate the diameter related effect. Moreover, the results of tests with variable amplitude loading suggest a rather conservative hypothesis of damage accumulation, considered in the Eurocode. Regarding the discrepancy of fatigue strength between uncoated and hot-dip galvanized HV-bolts ambiguous results are obtained for bolt sizes M36 and M64. Thus, the results put into question a superior fatigue classification of uncoated, black large-size HV-bolts, as for instance suggested in the VDI Guideline 2230. The systematically elaborated analytical fatigue assessment methodology, specifically refined for the application to large size HV-bolts, yields calculations in good agreement with experimental results for different bolt sizes and loading conditions. Thereby, an introduced engineering model also enables the calculation of the fatigue life for hot-dip galvanized bolts.",
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Download

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T1 - Fatigue assessment of large-size bolting assemblies for wind turbine support structures

AU - Eichstädt, Rasmus

PY - 2019

Y1 - 2019

N2 - High-strength ‘System HV’ bolting assemblies with large bolt diameters of M36 and bigger are frequently used in ring-flange connections in steel support structures for on- and offshore wind turbines. At the bottom parts of the supporting steel towers the magnitude of the acting loads usually requires the application of very large bolt diameters M64 or M72. The bolts are subjected to high cyclic loads with considerable numbers of load cycles and variable amplitudes. Thus, for reduction of fatigue loads, preloading of bolts with high forces is mandatory. Reliable protection against corrosion is commonly achieved by hot-dip galvanizing. It is known that the zinc coating has an impact on the fatigue strength of structural steel components. Moreover, the high mean stress level affects the bolts’ fatigue behaviour and thus needs to be appropriately considered in experimental as well as analytical fatigue analyses. Fatigue testing of HV-bolts with large diameters under a representative mean stress level imposes challenges to the required testing equipment. Hence, S-N curves in applicable design standards, in particular EN 1993-1-9, are mostly validated on tests with smaller bolts and the influence of an increased diameter is yet to be verified. Moreover, the quantitative effect of hot-dip galvanizing on the fatigue strength of large-size HV-bolts is still under investigation. Analytical fatigue assessment procedures provide valuable potentials to supplement expensive experimental test series and to discretely investigate specific impact factors with relevance to the fatigue strength. However, to this end suitable assessment methodologies need to be adapted and validated for the application to HV-bolts with large diameters as well as for an appropriate consideration of the effect of hot-dip galvanizing. This dissertation presents comprehensive research work on the experimental and analytical fatigue assessment of large-size HV-bolts. The performed fatigue tests extend the range of the experimental validation of normative regulations to a bolt diameter of M64, representative for the upper end of bolt sizes applied in today’s modern wind turbine support structures. Thereby, the safe applicability of the relevant fatigue class FAT 50 of the Eurocode 3 is confirmed. The comparison of performed tests on hot-dip galvanized bolts of diameters M36 and M64, as well as further analytical analyses, indicate a minor impact of the bolt size in the considered large diameter range. The corresponding reduction function of the Eurocode 3 thus tends to overestimate the diameter related effect. Moreover, the results of tests with variable amplitude loading suggest a rather conservative hypothesis of damage accumulation, considered in the Eurocode. Regarding the discrepancy of fatigue strength between uncoated and hot-dip galvanized HV-bolts ambiguous results are obtained for bolt sizes M36 and M64. Thus, the results put into question a superior fatigue classification of uncoated, black large-size HV-bolts, as for instance suggested in the VDI Guideline 2230. The systematically elaborated analytical fatigue assessment methodology, specifically refined for the application to large size HV-bolts, yields calculations in good agreement with experimental results for different bolt sizes and loading conditions. Thereby, an introduced engineering model also enables the calculation of the fatigue life for hot-dip galvanized bolts.

AB - High-strength ‘System HV’ bolting assemblies with large bolt diameters of M36 and bigger are frequently used in ring-flange connections in steel support structures for on- and offshore wind turbines. At the bottom parts of the supporting steel towers the magnitude of the acting loads usually requires the application of very large bolt diameters M64 or M72. The bolts are subjected to high cyclic loads with considerable numbers of load cycles and variable amplitudes. Thus, for reduction of fatigue loads, preloading of bolts with high forces is mandatory. Reliable protection against corrosion is commonly achieved by hot-dip galvanizing. It is known that the zinc coating has an impact on the fatigue strength of structural steel components. Moreover, the high mean stress level affects the bolts’ fatigue behaviour and thus needs to be appropriately considered in experimental as well as analytical fatigue analyses. Fatigue testing of HV-bolts with large diameters under a representative mean stress level imposes challenges to the required testing equipment. Hence, S-N curves in applicable design standards, in particular EN 1993-1-9, are mostly validated on tests with smaller bolts and the influence of an increased diameter is yet to be verified. Moreover, the quantitative effect of hot-dip galvanizing on the fatigue strength of large-size HV-bolts is still under investigation. Analytical fatigue assessment procedures provide valuable potentials to supplement expensive experimental test series and to discretely investigate specific impact factors with relevance to the fatigue strength. However, to this end suitable assessment methodologies need to be adapted and validated for the application to HV-bolts with large diameters as well as for an appropriate consideration of the effect of hot-dip galvanizing. This dissertation presents comprehensive research work on the experimental and analytical fatigue assessment of large-size HV-bolts. The performed fatigue tests extend the range of the experimental validation of normative regulations to a bolt diameter of M64, representative for the upper end of bolt sizes applied in today’s modern wind turbine support structures. Thereby, the safe applicability of the relevant fatigue class FAT 50 of the Eurocode 3 is confirmed. The comparison of performed tests on hot-dip galvanized bolts of diameters M36 and M64, as well as further analytical analyses, indicate a minor impact of the bolt size in the considered large diameter range. The corresponding reduction function of the Eurocode 3 thus tends to overestimate the diameter related effect. Moreover, the results of tests with variable amplitude loading suggest a rather conservative hypothesis of damage accumulation, considered in the Eurocode. Regarding the discrepancy of fatigue strength between uncoated and hot-dip galvanized HV-bolts ambiguous results are obtained for bolt sizes M36 and M64. Thus, the results put into question a superior fatigue classification of uncoated, black large-size HV-bolts, as for instance suggested in the VDI Guideline 2230. The systematically elaborated analytical fatigue assessment methodology, specifically refined for the application to large size HV-bolts, yields calculations in good agreement with experimental results for different bolt sizes and loading conditions. Thereby, an introduced engineering model also enables the calculation of the fatigue life for hot-dip galvanized bolts.

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