Offshore wind turbines (OWTs) are gaining prominence worldwide, and the hybrid pile-bucket foundation, which combines a monopole and a bucket, has emerged as a noteworthy development. In this study, a 3-D numerical model for the 5-MW OWT was constructed utilizing the OpenSees platform. The dynamic characteristics of the sand was modeled with the PDMY02 constitutive model and the soil was discretized using brick u-p elements. To investigate the dynamic behavior of the OWT in an actual marine environment, the coupled model was subjected to dynamic loadings, encompassing waves, wind, and earthquake. Two seismic motions with different frequency components were considered, respectively. The study focused on exploring the impacts of key influencing factors on the OWT rotation, tower-top acceleration development and spatiotemporal distribution of excess pore water pressure ratio (EPWPR). These factors include dynamic load combinations, earthquake intensity, soil relative density, wind speed, angle between load directions, and pile length. It is revealed that the inclination angle of offshore wind turbines (OWTs) may exceed the allowable threshold under specific conditions of load combinations, seismic motion inputs, and seabed conditions. Thus, it is suggested to appropriately consider the effects of wind and wave actions in the seismic analysis of OWTS.
Bell-spigot jointed ductile iron pipelines are increasingly used, which are highly susceptible to permanent ground deformation. It is necessary to predict their responses under normal fault conditions. This investigation presents an analytical approach that simplifies the pipeline as a beam-type structure resting on discrete Winkler foundation comprising discrete springs, connected by shear and torsional springs at the bell-spigot joints, which is solved by the finite difference method. Comparisons of pipe deflection and joint rotation with the results from two full-scale experiments confirm the effectiveness of this method. Parametric analysis is conducted with respect to soil modulus, location of peak curvature, burial condition, pipe diameter, and joint rotational stiffness. It is found that increase in soil modulus can deteriorate the deformation of pipe bodies. Concentration of shear zones intensifies the responses of both pipeline segments and bell-spigot joints. For deeply buried jointed pipelines, less compacted backfills can reduce the soil-pipe interaction forces, mitigating the detrimental impact of fault rupture. A concept of relative joint-pipe stiffness ratio, R, is introduced to describe different joint rotational stiffness, identifying the threshold of R = 10 % for transition between jointed and continuous pipelines. Considering different failure limits, joint rotation failure always occurs earlier than pipe bending failure.