The quest for clean, renewable energy resources has given a global rise in offshore wind turbine (OWT) construction. As OWTs are more exposed to harsh environmental conditions, the dynamic behavior of OWTs with jacket support structures under critical loading scenarios is crucial yet least understood, which becomes more convoluted with the consideration of soil-structure interaction (SSI) effects. In addition, the seismic characteristics of such systems heavily depend on the excitation characteristics like frequency content, a feature that is still ambiguous. This research aims to examine the influence of seismic frequency contents on the dynamic characteristics and damage modes of jacket-supported OWT systems including SSI effects. The numerical model is established and validated based on a previous study, which ensures the accuracy of the numerical modeling framework. Upon validation, extensive numerical analyses are performed under earthquakes with varying frequency contents. Results reveal the relationship among the ground motion frequency, SSI, and the dynamic and damage behavior of jacket-supported OWTs, offering important insights for the improved seismic design and analysis of jacket-supported OWTs.

Pipelines are important structural elements that are frequently used today to meet many infrastructures needs such as drainage, natural gas or water transmission. In this context, the usability of such structures, which are important elements of infrastructure systems, especially after disasters such as earthquakes, is of great importance. For this reason, within the scope of this study, a parametric investigation of the seismic behaviors of a natural gas pipeline system under mainshock-aftershock sequences have been carried out, specifically taking into account the soil-natural gas pipeline interaction (SNGPI) in the help of finite element model (FEM) proposed. Before developing the model of SNGPI system proposed using solid element, the fundamental mode frequencies of the pipeline system modeled using the solid element for the verification have been compared with those of obtained from the pipeline system modeled using the beam element and the analytical solutions. After verification of proposed model is demonstrated, SNGPI system has been modeled and its fundamental modes have been compared with mode frequencies of soil stratum obtained from well-known simple analytic solutions. After this stage, the dynamic analyses of natural gas pipeline (NGP) system in the time domain have been carried out using four different soil systems and four different mainshock-aftershock sequences. The results of the nonlinear time-history analyses have been investigated in terms of the stress and the displacement responses. Parametric evaluations show that the greatest displacements and the stresses occurring at the considered nodes of NGP system may be importantly affected from mainshock-aftershock sequences and soil stiffness changes. As the soil stiffness decreases, both the peak stresses and displacements increased significantly. On the other hand, the same responses obtained under mainshock loadings, which have relatively lower peak ground acceleration (PGA)/ peak ground velocity (PGV) ratio compared to aftershock loadings, are generally larger than those obtained under aftershock loadings.

Liquefaction poses a potential threat to the safety, serviceability and stability of shield tunnels during seismic events. This study investigates the seismic response of shield tunnels in liquefiable soils employing a fully coupled dynamic effective stress analysis model. The model accounts for the nonlinear mechanical behavior of the shield tunnel structure and incorporates the advanced bounding surface elastoplastic PM4Sand and PM4Silt models integrated with Biot u - p formulation to simulate the constitutive behavior of liquefiable and nonliquefiable soil layers. The seismic performance of shield tunnel -liquefiable soil system is evaluated considering ground motions with different characteristics in the transverse direction. The numerical results reveal the significant effects of ground motion frequency content and seismic intensity on the liquefaction triggering, the tunnel deformation and the internal forces of segmental joints. The soil -structure dynamic interaction and the soil shear dilatancy characteristics greatly influence the generation of the earthquake -induced excess pore water pressure and post -liquefaction shear strains. It is observed that the soil contact pressures on the left and right springlines of the tunnel experience larger increase compared to the contact pressure on the tunnel crown and invert. This observation suggests that the soil could cause racking deformation on both sides of the tunnel structure towards the center. Besides, the deformations and mechanical behaviors of the segmental joints around the tunnel left and right feet and the right springline are notably higher than at other joints in the saturated deposits. Furthermore, it is found that ground motion characterized by low -frequency contents, amplifies the seismic response of the soil and the tunnel when compared to the ground motions with high or moderatefrequency contents.

Featured Application The conclusions of this article can be used to predict the uplift of tunnels or underground structures induced by soil liquefaction considering vertical earthquake motion.Abstract The uplift of underground structures induced by soil liquefaction can damage underground structure systems. Numerical simulations have shown that uplift is positively correlated with the energy of horizontal input motion. However, the effects of vertical input motion on uplift have not been studied comprehensively in the past. Previous studies on the vertical motion concluded that the effects of vertical motion on uplift depend on the overall characteristics of earthquake motion. These motion characteristics have only been studied separately in previous studies. A comprehensive study to explore the interactions and overall effects of these characteristics on the uplift of underground structures is essential. In this study, the FLAC program with the PM4Sand model was used as a numerical tool to explore the effects of vertical input motion on the uplift of underground structures. The numerical model was calibrated using centrifuge test results, and 48 earthquake motions were selected as input motions to study the effects of the overall characteristics of earthquake motions on the uplift of underground structures. The simulation results show that the frequency content characteristics of horizontal and vertical motion are the major factors affecting the uplift magnitude and the responses of liquefiable soils. However, most simulation cases show that the inclusion of vertical motion causes a 10% difference in the tunnel uplift, compared to cases without vertical motion.