Abstract This paper describes a numerical method for ice load determination in conditions where a drifting ice floe acts on a vertical offshore structure. The model is based on a substructure technique where separate dynamic models of the interacting media and components are combined by a computer model. First, FE technique is used to model the structure. Second, complex impedance functions are used to consider the stiffness and damping properties of the foundation. Third, the action of the drifting ice floe is considered in two phases by adopting separate models for the elastic far field area and a nonlinear near field area adjacent to the ice–structure interface.