This paper presents comprehensive results on the mechanical behavior of submarine steel pipelines subjected to various strike-slip fault displacement loads. The investigation uses strain-based criteria to estimate pipeline performance based on rigorous numerical modeling and simulation of a soil–pipe system, accounting for nonlinear material behavior and large strain of both pipeline and surrounding seabed soil. Equivalent boundary conditions are derived and applied at both ends of the pipeline to take the effect of pipeline segments far away from the fault into account. Parameters affecting the response of submarine pipelines subjected to active faults (including pipe diameter, diameter-to-thickness ratio, burial depth, soil stiffness, and intersection angles) are studied. A uniform design experiment is also carried out to predict the critical fault displacement. The results show that the segments of the pipe embedded in both blocks near the fault plane are critical locations where buckling or rupture is more likely to occur. The ability of the pipeline to withstand more fault displacements can be enhanced by increasing the diameter and wall thickness. In addition, the choice of proper burial depth and differential pressure can lead to an increase in flexural stiffness and weaker soil–pipeline interaction. Pipe diameter, crossing angles, and burial depth determine the pipeline’s failure modes. An accurate regression derived from finite uniform design experiments is proposed for the performance-based design of future submarine pipelines.

The fatigue crack growth properties of G20Mn5QT cast steel and corresponding butt welds, using compact tension specimens, were monitored and investigated via acoustic emission (AE) techniques. Fatigue crack growth is a combination of cyclic plastic deformations before the crack tip, tensile crack fractures, and shear crack fractures. The cyclic plastic deformations release the maximum amount of energy, which accounts for half of the total energy, and the second-largest number of AE signals, which are of the continuous-wave type. The tensile crack fractures release the second-largest amount of energy and the largest number of AE signals, which are of the burst-wave type. The shear crack fractures release the least amount of energy and the lowest number of AE signals, which are similar to the burst type, albeit with a relatively longer rise time and duration. Crack tip advancement can be regarded as a discontinuous process. The critical area before the crack tip brittlely ruptures when the fatigue damage caused by cyclic plastic deformations reaches critical status. The ruptures produce a large number of tensile crack fractures and rare shear crack fractures. Through fractography observation, the shear crack fractures occur probabilistically around defects caused by casting or welding, which lead to stress and strain in the local complex.

With the continuous utilization of renewable energy, the number of onshore wind turbines is increasing. Small design improvements can save costs and facilitate the maintenance and repair of the wind turbine foundation. In this paper, an existing gravity expansion foundation with an anchor cage is improved. Our improvements further expand the space inside the foundation and reduce the length of the anchor bolt, which could reduce the costs and facilitate construction. To study the performance of the new foundation, a three-dimensional finite element model of the foundation–soil–anchor bolt was established via a finite element simulation. The damage evolution of the foundation was simulated with the concrete damage plasticity model (CDP). The separation ratio, foundation settlement, inclination ratio, reinforcement stress, foundation stress, and foundation damage of the new foundation under ultimate load conditions were analyzed. The influence of parameters h1 and b3 on the performance of the foundation was further studied. The finite element analysis results show that the tensile stress of concrete can be effectively reduced by appropriately increasing the corbel height and ring beam width of the foundation. The results also show that the improved wind turbine foundation force is reasonable and can meet the use of the actual project requirements on the level of finite element analysis.