Seismic response of large-scale prestressed concrete bucket foundation for offshore wind turbines

Abstract

Sandy ocean soil is vulnerable to liquefaction under seismic action. This paper describes the structural design of a new large-scale prestressed concrete bucket foundation (LSPCBF) for offshore wind turbines that take the seismic response of the foundation into consideration. Using an integrated finite element model of the soil, bucket foundation, and upper structure that incorporates infinite elements for the soil boundary, the dynamic responses of the upper structure, the bucket foundation, and the soil surrounding the bucket foundation to three types of seismic wave acceleration time histories were determined using time history analysis. The Shanghai artificial seismic wave was used as an example. This wave causes the most intense seismic response of the seismic waves considered, based on the anti-liquefaction shear stress approach to estimating the area of soil liquefaction. The results showed that 88% of the soil outside the bucket in the range of the bucket depth is liquefied. In contrast, only 9% of the soil inside the bucket is liquefied. As the soil depth increases, the liquefaction range decreases substantially. The simulation results show that the LSPCBF can improve the liquefaction resistance of soil inside and directly below the bucket under seismic loading. Finally, the foundation stabilities under an ultimate load before and after an earthquake were compared. The horizontal displacement of the liquefied foundation increased by 41.1% and the vertical differential settlement increased by 6.2% after the earthquake. A large plastic zone was not formed, which means that an LSPCBF subjected to seismic action is still able to support the ultimate load.

Wind turbines and seismic hazard: a state-of-the-art review

“…A similar type of a large concrete bucket foundation was also analyzed in the time domain by Zhang et al . . They developed a detailed FE model, which was excited by three strong ground motions selected on the basis of the Chinese design code.…”

“…The latter was profound for the large pile sizes typical of the offshore wind turbines. The high computational sources required for the dynamic analysis of the entire FE model (i.e., consisting of the wind turbine along with the underneath soil‐foundation system) did not inhibit other researches from applying this time‐costly procedure to elaborate the SSI effects on wind turbines seismic performance (e.g.,). Along these lines, Prowell et al .…”

Anti-liquefaction characteristics of composite bucket foundations for offshore wind turbines

“…However, the anti-liquefaction effect of the composite bucket foundation has an obvious advantage because the high overburden pressure of the large-scale concrete structure and the circle constraints of the bucket on the inner soil can greatly improve the liquefaction resistance of the inner soil. 11 The cyclic liquefaction resistance of the soil inside or directly below the bucket foundation is much larger than that outside the bucket foundation. The bucket applies confining pressure, which greatly improves the liquefaction resistance of the inner soil.…”

Field experiments on wet tows of an integrated transportation and installation vessel with two bucket foundations for offshore wind turbines

“…The new foundation innovated by a research group at Tianjin University is based on the conventional bucket foundation and, for the first time, which are proposed as a composite bucket foundation for offshore wind turbines suitable for the marine area offshore of China (high wind speeds and soft ground) Liu et al, 2014;Lian et al, 2012Lian et al, , 2014Zhang et al, 2014Zhang et al, , 2015Zhang et al, ,a, 2015b. The only CBF for a fully operational wind turbine of 2.5 MW was installed at the offshore test facility in Qidong City in the southeast of Jiangsu province in China in 2010.…”