Publication Abstract

International Symposium on Frontiers in Offshore Geotechnics, (DFI)

Methods of Numerical Analysis of Monopiles under Pseudo-Random Lateral Loading
Guy T. Houlsby, Byron W. Byrne, Harvey J. Burd and Toby D. Balaam

Monopiles, 8m in diameter or even larger, are the preferred foundation option for most offshore wind turbines. However, there is significant economic pressure to eliminate unnecessary conservatism in design, both to reduce the costs and to extend the scope of monopiles to larger turbines and deeper water. The PISA project, on the development of design methods for monopiles, focussed on monotonic unidirectional loading. However, the real loading is multi-directional and pseudo-random, with multiple components of frequency and amplitude. This paper outlines the development of theoretical and numerical methods for monopiles that are being developed to extend the PISA methods to cyclic loading. They are intended to capture the long term effects of very large numbers (>10/sup 7/) of cycles, including (a) changes of stiffness, (b) changes of energy loss factor, (c) accumulated displacement and (d) post-cyclic monotonic response to ULS loading. The methods are based on the HARM framework (Houlsby et al. 2017), allowing detailed modelling of the multidirectional load history without the need to idealise this into binned packets of regular cycles. This contrasts with most current approaches, which employ rule-based modifications to monotonic design curves. The methods can be implemented either at the macro-element level or as generalised Winkler models for the soil reactions along the length of the pile.

 article #3553; publication #1069 (IC-ISFOG21)