Systematic Testing of the Fatigue Performance of Submerged Small-Scale Grouted Joints

Abstract

With an increasing demand for renewable energy, offshore wind farms become more and more important. Within the next 15 years the German government intends to realize offshore wind farms with a capacity of 15 GW of electrical energy. This corresponds to approximately 3000 to 4000 new turbines. The grouted joint is a common structural detail for the connection between substructure and foundation piles in offshore wind turbine structures. For lattice substructures such as jackets, the connection is located just above the seabed and is permanently surrounded by water. Prior investigations by Schaumann et al. showed that the surrounding water may have an impact on the fatigue performance of grouted joint specimens. Thus far, very few results of submerged fatigue tests on grouted joint specimens are published and their statistical reliability is insecure. Within this paper, 24 individual test results are presented. Regarding test parameters, the focus is set on two different applied load levels, two different loading frequencies and two different grout materials. All parameters are varied in a factorial experiment and are statistically evaluated. The evaluation shows that load level and loading frequency have a significant effect on the fatigue performance of the connection. Moreover, both effects are significantly correlated. For the used grout materials no significant impact is visible, which can be explained by their similarity regarding mechanical properties and micro structure. Furthermore, the mean displacement and the stiffness degradation of the specimens during fatigue tests are discussed in detail in the paper. In conclusion, previously published results on the fatigue performance of submerged small scale grouted joint specimens can be confirmed. Load level as well as loading frequency can be stated as most relevant parameters for the fatigue performance.

Impact of Water on the Fatigue Performance of Large-Scale Grouted Connection Tests

“…First off all, these results confirm the findings of the smallscale fatigue tests regarding the influence of water reducing the number of endurable load cycles [20,21]. And secondly, the influence of the grout layer thickness reducing the fatigue performance [27] is also valid for tests in wet AC.…”

“…Both specimens tested in wet AC are loaded at a constant frequency of 1 Hz to exclude effects of the known loading frequency effect for submerged grout connection tests (cf. [22]).…”

“…The small-scale fatigue tests were carried out in dry and wet ambient conditions (AC) and revealed a significant impact of the AC (cf. [20,21]). Submerged specimens endured a lower amount of load cycles compared to specimens tested in dry AC.…”

“…Moreover, for tests in wet AC a loading frequency dependent fatigue behaviour was identified (cf. [22]) leading to less endurable load cycles at higher loading frequencies. The investigated frequencies were in the range of 0.3 Hz to 10 Hz.…”

Zum Ermüdungsverhalten von Grout‐Verbindungen bei unterschiedlichen Umgebungsbedingungen

“…Insgesamt wurden sechs Versuche für trockene sowie 26 für nasse Umgebungsbedingungen durchgeführt und ausgewertet. Begleitende Materialuntersuchungen [10] zeigten signifikante Unterschiede zwischen den Festigkeitsangaben der Hersteller und den tatsächlichen Werten. Die realen Festigkeitsunterschiede zwischen den beiden Materialien waren statistisch nicht signifikant, so dass eine Vernachlässigung des Materialeinflusses in der Auswertung zulässig ist.…”