Accurately capturing the seismic response of underground structures subjected to obliquely incident seismic waves, particularly when the angle of incidence surpasses the critical value, remains a challenging task in earthquake engineering. To address this gap, this paper presents a three-dimensional (3D) nonlinear seismic analysis of subway stations embedded in a layered site, specifically in response to obliquely incident shear (SV) waves at arbitrary angles. An innovative procedure, termed the coupled dynamic stiffness matrix-finite element method (DSM-FEM), is introduced to enable seismic input by transforming responses induced by arbitrarily incoming SV waves into equivalent nodal loads. To accurately simulate wave propagation within the site, a viscous-spring artificial boundary is utilized, while a nonlinear generalized Masing model that incorporates modified damping is employed. Using the Daikai subway station as a benchmark, the research examines the effects of varying oblique incident angles on the structural response, taking into account dynamic soil-structure interaction. The results reveal that the maximum response, including peak deformation, internal forces, Mises stress, occurs when the incident angle approaches the critical value. Beyond this critical angle, the seismic response notably diminishes. Additionally, the influence of horizontal incident angles is found to be noticeable, leading to variations in deformation patterns and internal forces across different structural components. Specifically, it has been observed that the drift ratio, displacement, shear force, acceleration, and Mises stress exhibit a decreasing trend as the horizontal incident angles increase. These findings highlight the significance of considering non-vertical input ground motion in seismic analysis, and offer valuable insights for the structural design and safety evaluation of underground structures.

Historic bridges are invaluable cultural landmarks that embody the architectural and engineering achievements of past civilizations. Preserving these structures, which are often vulnerable to seismic activity, is essential to safeguarding cultural heritage for future generations. This study examines the Bat & imath;ayaz Bridge, which sustained significant damage in the February 8, 2023, Kahramanmaras,earthquakes. Originally, iron connectors were used between stones in the arch of the bridge. This research investigates the potential of using FRP (Fiber Reinforced Polymer) connectors as an alternative to iron for enhancing the seismic resilience of the arch. The bridge was reinforced with both FRP-metal clamps and dowel connectors, enabling a comparison of its seismic performance under each configuration. The connectors were carefully installed between stones with specialized adhesives and Khorasan mortar. Reinforced stone elements then underwent compressive and tensile testing, yielding essential data on the connectors' normal and shear stiffness, as well as the mechanical properties of the Khorasan mortar. A three-dimensional model of the bridge was created in FLAC3D software using the finite difference method. Individual stone elements were modeled with brick and wedge components, incorporating experimentally derived stiffness values. The Mohr-Coulomb material model was applied to both the stone elements and the foundation soil, with non-reflecting boundary conditions set at the model's edges. Ten different ground motion simulations were conducted to assess seismic behavior. The seismic analyses for the two models, with FRP and metal connectors in the arch, indicated that both types significantly improved the bridge's seismic resistance. Results revealed that the use of FRP and iron mechanical connectors in the arch substantially modified the bridge's seismic response compared to the configuration without connectors. Besides, no major differences were observed between FRP and iron connectors in terms of enhancing seismic resilience of the bridge. The findings suggest that corrosion-resistant FRP connectors provide a durable alternative to metal connectors, which are prone to degradation over time. Thus, FRP connectors represent a promising option for the long-term seismic strengthening and restoration of historic bridges.

Stability analysis of undrained anisotropic slopes has been made by a semi-analytical approach. The variational calculus is employed to find the critical sliding surface and the extremized resistance functional for general undrained anisotropic materials in seismic condition. A complete set of formulation with the solution is presented. In this approach, no failure surface is assumed and it is obtained throughout the solution procedure. The semi-analytical solution highly increases the efficiency of the computational effort and the accuracy of the results. The stability factor is reported for a series of anisotropic slopes in undrained condition subject to a range of pseudo-static earthquake accelerations. Finally, the results are interpreted and discussed by AI to make a comparison between a manual and an AI-assisted interpretations.

Accurate structural health monitoring (SHM) is crucial for ensuring safety and preventing catastrophic failures. However, conventional parameter identification methods often assume a fixed-base foundation, neglecting the significant influence of soil-structure interaction (SSI) on the dynamic response, leading to inaccurate damage assessments, especially under seismic loading. Therefore, we introduce a novel approach that explicitly incorporates SSI effects into parameter identification for frame structures, utilizing an optimized variational mode decomposition (VMD) technique. The core innovation is the application of the Subtraction Average-Based Optimizer (SABO) algorithm, coupled with permutation entropy as the fitness function, to optimize the critical VMD parameters. This SABO-VMD method was rigorously validated through a shaking table test on a 12-story frame structure on soft soil. Comparative analysis with EMD and conventional VMD demonstrated that SABO-VMD provides a superior time-frequency representation of the structural response, capturing non-stationary characteristics more effectively. A novel energy entropy index, derived from the SABO-VMD output with SSI, was developed for quantitative damage assessment. It revealed 8.1% lower degree of structural damage compared to the fixed-base assumption. The proposed SABO-VMD-based approach, by explicitly accounting for SSI, offers a substantial advancement in SHM of frame structures, leading to more reliable safety evaluations and improved seismic resilience.

As critical lifeline projects, complex geological conditions affect urban buried pipelines, making their seismic safety particularly important. This study focused on a high-pressure gas pipeline project in a city to establish a static and dynamic joint analysis model of the pipeline foundation interaction system using ANSYS software. Considering various working conditions, the seismic response analysis of high-pressure pipelines under different laying methods, changes in buried depth, and bending angles was carried out. The results show the radial deformation peak of the deeply buried pipeline under the action of earthquake increases by 106.17%, which is more vulnerable to damage. The depth of soil cover significantly impacts the dynamic response of buried pipelines. Pipes should be buried shallowly, while meeting the minimum depth of soil cover and other specifications. The two 18 degrees bends are in the peak area of axial high strain, and the buried pipelines are more prone to stress concentration at the large angle bends, which should be primarily monitored. The research results can provide references for the seismic safety analysis of buried high-pressure gas long-distance pipelines in similar urban settings.

This study presents the design and structural analysis of a bridge to protect two natural gas pipelines against static and dynamic loads resulting from a new railway line to be constructed above them. Structural analyses were conducted considering earthquake effects, particularly using the load combinations and coefficients recommended by AASHTO LRFD [2017]. The railway bridge is not designed to span any crossings. However, since the existing railroad is situated directly on the ground, a train load is transferred to the pipelines through the ground. To reduce this load transfer, a 25-30cm gap is maintained between the deck and the ground in this protective bridge design proposal. The maximum anticipated displacement of the bridge was considered in the analysis. Site-Specific Earthquake Hazard Analysis was first performed for the proposed bridge due to the critical implications of the pipelines. In the second stage, the structure underwent nonlinear dynamic displacement loading and bridge-pile-soil interaction was analyzed using both linear and nonlinear methods. The performance targets - Uninterrupted Use for DD2a class ground motion and Controlled Damage for DD1 earthquake) - stipulated by the Turkish Bridge Design Standards [TBDS, 2020] were evaluated using strength-based linear and strain-based nonlinear analyses. The results confirmed that the proposed bridge satisfied all target safety levels. In conclusion, this study aims to guide both designers and practitioners, as it is among the first to address the newly enacted TBDS-2020 regulation in Turkiye and serves as an exemplary engineering solution for similar protective bridge designs.

The seismic performance of a long-span triple-tower suspension bridge is a critical consideration in engineering communities. To promote a better seismic design, this paper presents a parametric study on the structural seismic control using hysteretic steel dampers. The finite element model is firstly established, and an introduction to the mechanical properties of the E-shaped hysteretic steel damper is made. Then, a seismic analysis is conducted under uniform earthquake excitations. Considering the effect of wave passage, the performance of hysteretic steel dampers in seismic control is further analyzed. The results indicate that the travelling wave effect greatly affects seismic responses. Increasing the damper elastic stiffness can effectively reduce the relative displacement between the main girder and either the left or the central tower. This treatment is effective for the right tower only when the wave velocity is among 400-1600 m/s, while it makes little contribution in other ranges. At an arbitrary wave velocity, increasing the damper elastic stiffness would cause minor changes to the shear forces of side towers, while its influence on the central tower is significant. A reasonable damper design for the long-span triple-tower suspension bridge depends on an essential prior evaluation of the wave velocity based on soil conditions.

It is crucial to simulate the seismic behavior of offshore wind turbines, especially when dealing with foundations on non-cohesive soil. There is a risk of liquefaction occurring, which highlights the need to obtain values of excess pore water pressure. In this study, we created a three-dimensional model of a caisson foundation for an offshore wind turbine on loose sandy soil from the Syrian coast. The Mohr-Coulomb constitutive plasticity model was used to analyze two scenarios. The first scenario involved applying wind and earthquake loads, while the second scenario included marine currents and wave loads in addition to the wind and earthquake loads. We used Coupled acoustic-structural medium analysis after confirming its effectiveness on the soil through comparison with simulation results of the FLAC3D program from a previous study. The numerical modeling results indicated that it is possible to use Coupled acoustic-structural analysis in soil and water modeling. The study monitored the values of excess pore water pressure and found that liquefaction occurred in the soil due to the earthquake. The analysis also highlighted the importance of considering wave and marine currents loads in analyzing these structures. While these factors had a slight impact on excess pore pressure values, they significantly affected the directions and values of displacements.

The research aims to investigate and compare the seismic responses of various models, including free field, pile group, fixed base, and shallow/deep foundation-structure with different structural height-to-width ratios (h/b) in saturated and dry sands during realistic earthquakes with varying intensities to ascertain whether soilfoundation-structure-interaction (SFSI) has beneficial or detrimental effects. To date, no comparative research has considered the response of shallow and deep foundations in both saturated and dry soil simultaneously. This study addresses this gap using 3D non-linear parallel finite element models validated with two distinct sets of centrifuge tests, and the extended analysis of nonlinearity effects of seismic SFSI considering large deformation performed. Focusing on the time-frequency content distribution result, the input acceleration amplitudes at different times are intensified by passing through the stiffer system (e.g., dry site, remediated soil, and shorter structure) at high frequencies. Conversely, they decrease in a softer system, especially in liquefiable soil, due to the excess pore pressure build-up. The time of PGA alters at the foundation level, and correspondingly, the commencement time of significant settlement occurs quicker or later. A structure with a more flexible base exhibits greater rocking and a reduction in flexural drifts, internal forces, and base shear force to seismic weight ratio. This subsequently results in a decrease in the local damage sustained by the structure. In contrast to lower h/b, the structural base shear force in the saturated soil site is greater than in the dry one, due to the higher peak structural acceleration.

Damage to buried pipes under seismic landslide actions has been reported in many post-earthquake reconnaissance. The landslide-pipe problem in the technical literature has been often investigated using simplified analytical methods. However, the analytical methods ignore the real mechanism of pipe response under natural dynamic slope instability. The dynamic slope instability is significantly influenced by its lateral boundary interface (LBI) characteristics. In this study, slope-pipe interaction (SPI) under seismic loading, focusing on the effect of LBI properties, is evaluated by continuum numerical simulation using the SANISAND constitutive model in FLAC3D. The results show that the geometry of the failure mass varies from 2D to 3D by increasing the stiffness at the slope boundaries (from smooth to hard) and the maximum pipe deformation decreases by around 40%. Moreover, the response components of maximum axial stress, bending moment, and shear stress of the pipe occur at the end sections of the buried pipe and near the boundaries of the landslide zone. However, the maximum pipe deflection occurs in the middle of the pipe. The results of shear force-shear displacement curves demonstrate that the soil-pipe interaction stiffness is variable along the pipe length and can be estimated by a hyperbolic equation.