ABSTRACT
Monopile foundations supporting offshore wind turbines experience cyclic lateral loading due to wind, waves and turbine operation. This loading varies in amplitude, frequency and direction. Understanding and predicting the monopile’s response to cyclic lateral loading is necessary for optimised design, as it can lead to permanent foundation rotation and evolution of the foundation’s dynamic response. This paper describes new laboratory apparatus designed to perform computer-controlled cyclic load tests on model-scale monopiles. Two perpendicular electric actuators facilitate multi-directional loading, with the apparatus capable of applying loads that continuously vary in amplitude, frequency and direction. Resolution of the instrumentation is also sufficient to capture the response, including accumulation of ratcheting rotation, at low loads. Results in cohesionless soil demonstrate the capabilities of the new apparatus, begin to reveal the monopile’s response to variable cyclic loading, and will allow validation of a recently developed design method for monopiles under cyclic lateral loading.
