Details
| Translated title of the contribution | Ermüdungsbewertung sehr großer Schraubenverbindungen für Tragstrukturen von Windenergieanlagen |
|---|---|
| Original language | English |
| Qualification | Doctor of Engineering |
| Awarding Institution | |
| Supervised by |
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| Date of Award | 28 Jun 2019 |
| Place of Publication | Hannover |
| Publication status | Published - 2019 |
Abstract
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Hannover, 2019. 214 p.
Research output: Thesis › Doctoral thesis
}
TY - BOOK
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.
U2 - 10.15488/5157
DO - 10.15488/5157
M3 - Doctoral thesis
CY - Hannover
ER -