1 g Model Tests on the Displacement Accumulation of Large-Diameter Piles Under Cyclic Lateral Loading

Large-diameter monopiles are an established foundation type for offshore wind energy converters. A crucial aspect in the design of such piles is the bearing behavior under cyclically acting wind and wave loads, namely the accumulation of deflections and rotations under these loads. Regarding the prediction of the behavior under cyclic one-way load, some empirical approaches and also numerical simulation methods exist. In contrast, the behavior under cyclic two-way loading is widely unclear and must be investigated by pile tests. This paper presents the results of 1 g model tests with large-diameter piles in sand under arbitrary cyclic loading types. It was found that for almost rigid large-diameter piles, the effect of the loading type on the rate of displacement accumulation could be accounted for by a function which is almost independent on the system parameters, e.g., pile stiffness or relative density of the sand, but dependent on load eccentricity. The maximum accumulation rate occurs for asymmetric two-way loading. Using the functions found in the tests, a prediction of displacement accumulation for load spectra consisting of packages of arbitrary loads becomes possible. For flexible piles, a different effect of the loading type on the rate of displacement accumulation was observed. Here, asymmetric two-way loading was obviously not more unfavorable than one-way load.