Timoshenko beam theory–based analytical solution of laterally loaded large-diameter monopiles

Abstract

Monopiles are one of the major types of foundation systems for offshore wind turbines. To obtain the responses of large-diameter monopiles under lateral loading, a four–spring beam model is proposed based on the Timoshenko beam theory, which considers lateral soil resistance, pile shaft resistance, base horizontal force, and base moment. All the soil resistance components are represented by a series of distributed and concentrated springs deployed along the pile shaft and at the pile tip, respectively. The solutions for the internal forces and deformations are derived using the state space method for the nonlinear pile–soil interaction and then validated by recent field pile tests and numerical simulations. Furthermore, a parametric study is undertaken to examine the influences of pile diameter, embedded length, wall thickness, lateral load and soil stiffness on the pile responses. The results show that increasing the pile diameter and lateral load or decreasing the pile embedded length causes the pile deformation pattern to transform from a relatively flexible bending mode to a rigid rotational mode. Moreover, increasing the pile diameter reduces the pile deformations, and the distributed moment, base horizontal force, and base moment may have more significant contributions on the lateral bearing capacity of the monopile.