Numerical study of diameter effect on accumulated deformation of laterally loaded monopiles in sand

Abstract

The design of offshore monopile is generally governed by the accumulated deformation under lateral cyclic loading, e.g. loads induced by winds and waves. Although methods have been proposed to predict the accumulated deformation of laterally loaded monopiles under cyclic loading, these models are mainly based on small diameter pile test results with number of load cycles far less than that experienced by an offshore wind turbine during its lifetime. Additionally, the effect of monopile dimension, e.g. diameter effect, on the cyclic response of monopile is not well examined. Based on the degradation stiffness model, this paper investigates diameter effect of monopiles on the accumulated deformation via a finite difference program, which shows that pile diameter has a remarkable influence on the development rate of the accumulated deformation of laterally loaded monopiles. A design model, which takes account of the effect of loading cycle numbers, load amplitudes and monopile diameter, is proposed based on a series of numerical simulation. The proposed design model is validated against measured results from field test and centrifuge test on cyclically loaded monopiles, which proves the validity of the proposed design model.

Keywords:

• Diameter effect
• monopile
• lateral cyclic load
• accumulated deformation
• sand

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The authors acknowledge the funding received from National Natural Science Foundation of China (Grant No. 41502273 and No. 41372274) and Program for Young Excellent Talents in Tongji University (Grant No. 2015KJ009) for supporting this research.