Derivation of cyclic p-y curves for the design of monopiles in sand

As foundation for offshore wind energy converters, the monopile has proven to be an economic and robust solution. In design practice, usually the p-y method is applied in the calculation of the monopile behavior. Here, the effect of cyclic loading with varying number of load cycles must be considered. A simple-to-use approach for the derivation of cyclic p-y curves would be highly desirable, which just modifies a chosen static p-y curve depending on the number of load cycles and other relevant parameters. A calculation approach termed "Stiffness Degradation Method (SDM)" has been applied to calculate pile deflection lines and bedding resistances of monopiles embedded in sand dependent on the actual number of cycles of a given load and with that also p-y curves for a given number of load cycles. The obtained results were utilized for the development of an approach to derive cyclic p-y curves for a given load cycle number based on a chosen static p-y model (cyclic p-y overlay model). The results show that a y-multiplier approach is suitable to account for the effect of cyclic loading. The proposed calculation approach gives the y-multiplier dependent on number of load cycles, pile geometry, load eccentricity and considered depth.