This paper proposes a carbon fiber reinforced polymer (CFRP) retrofitting scheme for improving the seismic performance of atrium-style metro stations (AMS). Past experimental studies have confirmed that the weakest of the AMS during strong earthquakes is located at the upper-story beam ends. However, there is thus far no candidate for a reference approach to retrofitting and strengthening the AMS. This study addresses this gap by applying CFRP retrofitting to both ends of the upper-story beam. The main objective is to assess the effectiveness of the proposed retrofitting scheme. First, a three-dimensional finite element model is developed to simulate dynamic soil-AMS interaction. The validity of the numerical method is assessed via a comparison with measured data from reduced-scale model tests. Second, a numerical model of the AMS retrofitted with CFRP is built using validated methods. Finally, dynamic time-history analyses of the AMS with and without CFRP retrofitting are conducted, and their dynamic responses, including inter-story drift, dynamic strain, and tensile damage, in conjunction with the lateral displacement of the surrounding ground, are compared. Comparison of the results for the non-retrofitted and retrofitted structures shows that CFRP retrofitting significantly reduces both the principal strains and tensile damage factors at the upper-story beam ends while slightly increasing those values at the mid-span of the beam; additionally, it does not change the structural lateral deformation. Therefore, it can be concluded that CFRP retrofitting could effectively improve the seismic performance of the AMS without changing its lateral stiffness.

The influence of seismic history on the liquefaction resistance of saturated sand is a complex process that remains incompletely understood. Large earthquakes often consist of foreshocks, mainshocks, and aftershocks with varying magnitudes and irregular time intervals. In this context, sandy soils undergo two interdependent processes: (i) partial excess pore water pressure (EPWP) generation during foreshocks or moderate mainshocks, where seismic loadings elevate EPWP without causing full liquefaction and (ii) incomplete EPWP dissipation between seismic events due to restricted drainage. These processes leave behind persistent residual EPWP, reducing the liquefaction resistance during subsequent shaking. A series of cyclic triaxial tests simulating these mechanisms revealed that liquefaction resistance increases when the EPWP ratio r(u) < 0.6-0.8 (peaking at r(u) similar to 0.4) but decreases sharply at higher r(u). Crucially, EPWP generation during seismic loading plays a dominant role in resistance evolution compared to reconsolidation effects. Threshold lines (TLs) mapping r(u), the reconsolidation ratio (RR), and peak resistance interval (the range of r(u) where the peak liquefaction resistance is located) indicates that resistance decreases above TLs and increases below them, with higher cyclic stress ratios (CSR) weakening these effects. These findings provide a unified framework for assessing liquefaction risks under realistic multi-stage seismic scenarios.

Creep, once considered an inherent characteristic of granular materials, is primarily governed by time and the current stress state. However, recent studies indicate that creep development is also influenced by the loading history. To better reveal the creep revolution law of the rockfill under the influence of loading history such as historical stress rates, creep tests were conducted under oedometric loading. Alternative loading-creep steps, different stress increment sizes, and various precreep stress rates were considered. Independent of other factors, the development of the creep rate was governed by the recent precreep stress rate (the prior stress rate defined in this study). When the prior stress rate was higher than a threshold value, the relationship between the creep rate and time was double logarithmic linear; thus the creep strain-time relationship tended to converge on a power law (referred to as the creep baseline herein). However, when the prior stress rate was lower than the threshold value, the initial creep rate was lower than that of the creep baseline and did not decrease until several minutes after the start of the creep. The development of the creep rate with time in the initial stage can be generalized as a straight horizontal line, suggesting that the rate remains almost unchanged for a certain time, until the straight horizontal line approached the creep baseline. The inheritance and hysteresis of different strain rates in the initial stage of subsequent creep resulted in differences in the creep magnitude and time development process of the creep rate. The above findings are constructive for predicting the deformation of deep layers of rockfill, such as embankments, with more accuracy, especially for that with some large-sized rigid-structure buildings on its surface.

The study focuses on the architectural and structural analysis of the Justinian Bridge, an ancient stone arch bridge dating from the Byzantine era, located on Turkey's Sakarya (Sangarius) River. The research examines the structural configuration of the bridge and integrates its architectural background with data derived from comprehensive analyses. Experimental geophysical investigations were employed to assess the bridge's structural behavior, particularly considering the depths of the piers embedded in alluvial soil layers. The studies provided valuable data on the geometric and hydraulic properties of the bridge piers. The bridge's natural vibration frequencies and mode shapes were determined using a three-dimensional finite element model under four different boundary conditions. The results revealed that natural vibration frequencies are sensitive to soil properties. Time history analysis, incorporating ten sets of ground motion data, evaluated the bridge's dynamic response to earthquake loads. The damage distribution on the bridge body was determined and compared with the stresses obtained from the numerical analysis. The numerical results accurately show the damaged areas of the bridge. The findings provide valuable insights into the safety of historic stone arch bridges and serve as an essential reference for future conservation efforts.

The Sand Compaction Pile (SCP) method is a widely utilized ground improvement technology that enhances the density of the ground by constructing sand piles through penetration and repeated withdrawal/re-driving of a casing pipe. This method is the most widely used liquefaction countermeasure method in Japan. While the improvement effect of SCP is predominantly attributed to the resultant increase in soil density, recent studies have suggested that the stress history (such as increased lateral pressure and shear history) induced during the SCP work process also contributes significantly to its effectiveness. In order to more accurately reproduce the behavior of the ground during the construction of Sand Piles, the stress history simulating the SCP work process was applied to specimens in hollow cylindrical torsional shear tests, and the effects of the stress history were observed. The specimens were initially consolidated with a lateral stress ratio of 0.5 (K0 = 0.5). Subsequently, a stress history including increased lateral stress and cyclic shear stress was applied. Finally, liquefaction resistance was assessed through cyclic loading. After applying the stress history, an increase in liquefaction resistance was observed in these specimens. This increase was larger than that of specimens subjected only to a lateral stress increase without the shear stress history. This increasing trend persisted even after the lateral stress was reduced following the application of stress history. Finally, these test results were analyzed to assess the impact of stress history on liquefaction resistance by comparing them with the relationship between relative density and the liquefaction resistance. (c) 2025 Japanese Geotechnical Society. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

Soil displacement along Balboa Boulevard during the 1994 Northridge earthquake ruptured natural gas transmission and distribution pipelines as well as two pressurized water trunk lines. Four other buried pipelines in the ground displacement zone were not damaged. This study probabilistically assesses the performance of the buried pipelines in the framework of performance-based earthquake engineering. The main aspects of pipeline performance follow from the geotechnical characteristics of the site. Uncertainty in each of the key soil-pipeline system parameters is estimated, including length of the seismic ground displacement zone, amount of seismic ground displacement, soil-pipeline interface shear stress, pipe steel yield strength and Young's modulus, and shapes of the pipe steel stress-strain curves. Monte Carlo simulations are performed with an analytical model to assess the pipe strain response. New fragility functions are proposed to evaluate pipeline performance in response to tensile or compressive longitudinal strain. The resulting probabilities of failure are compared with the results of a conventional analysis in which the modeled pipeline strains are evaluated with respect to the critical strains that cause either tensile or compressive failure. The failure probabilities compare well with the pipeline performance observed during the Northridge earthquake, except for one natural gas transmission line. A sensitivity analysis is performed for this line to investigate the reasons for the discrepancy. Advantages and limitations of probabilistic analyses are discussed.

Soil-pile interaction damping plays a crucial role in reducing wind turbine loads and fatigue damage in monopile foundations, thus aiding in the optimized design of offshore wind structures and lowering construction and installation costs. Investigating the damping properties at the element level is essential for studying monopole-soil damping. Given the widespread distribution of silty clay in China's seas, it is vital to conduct targeted studies on its damping characteristics. The damping ratio across the entire strain range is measured using a combination of resonant column and cyclic simple shear tests, with the results compared to predictions from widely used empirical models. The results indicate that the damping ratio-strain curve for silty clay remains S-shaped, with similar properties observed between overconsolidated and normally consolidated silty clay. While empirical models accurately predict the damping ratio at low strain levels, they tend to overestimate it at medium-to-high strain levels. This discrepancy should be considered when using empirical models in the absence of experimental data for engineering applications. The results in this study are significant for offshore wind earthquake engineering and structural optimization.

This study investigates the seismic performance of a theoretical hospital building designed as a Fixed-Base (FB) structure according to TSC-2018 (Turkish Seismic Code) and evaluates its behavior under three scenarios: FixedBase (FB), Soil-Structure Interaction (SSI), and Base-Isolated (SSI+ISO). The study employs Nonlinear Time History Analysis (NLTHA) using scaled acceleration records, including one from the 2023 Maras, earthquake. Structural performance is assessed based on maximum roof displacements, interstory drift ratios (IDR), and isolator displacements. Results show that base isolation systems significantly reduce drift demands and roof displacements, keeping the structure within slight damage limits even under extreme seismic loads. In contrast, SSI effects amplify interstory drift demands, increasing the likelihood of exceeding moderate damage thresholds. The analysis highlights the Maras, Education and Research Hospital, which suffered severe damage and became non-operational during the 2023 Kahramanmaras earthquake. This outcome underscores the limitations of fixedbase designs in regions with soft soil conditions and the necessity of incorporating base isolation systems to improve seismic resilience. The findings emphasize the importance of mandatory adoption of base isolation systems in hospital designs, proper consideration of SSI effects, and the retrofitting of existing hospital buildings to meet modern seismic code requirements (TSC-2018) and prevent similar failures in future seismic events.

The significant reduction in the stiffness of liquefied soil is accompanied by a decrease in the shear wave velocity, which ultimately results in the softening of the liquefied site. Time-frequency response analysis can identify the sudden drop in the frequency of the liquefied site, which has been widely employed to determine the onset of liquefaction. However, using the modal frequency (corresponding to the maximum power at each time step) to identify the timing of liquefaction (tL) captures the reduction in frequency during earthquakes, but it does not encompass the entire range of frequencies that have changed. Furthermore, previous literature defines tL as the boundary separating the modal frequency into pre- and postliquefaction time segments, but this estimate does not consider the generation of pore water pressure. Two representative case histories are presented to highlight the limitations of identifying tL by solely relying on the modal frequency approach that uses a two-step function. As a result, this study introduces an innovative method to identify tL utilizing the spectral energy ratio (SER), which captures the entire frequency shift. A step-by-step procedure using SER is detailed, and the new estimates of tL are compared with those derived from previous literature using 30 case histories. To validate the approach, a sensitivity analysis was performed using centrifuge test data from the Liquefaction Experiment and Analysis Projects. Results indicated that incorporating a ramp that accounts for pore water pressure buildup in the trilinear function improved tL estimation. An optimized SER value of 0.92 was determined for the proposed method. The notable contribution of this study is an enhanced approach of identifying the timing of liquefaction triggering by only utilizing acceleration records without requiring pore water pressure responses.

In the seismic design of steel moment-resisting frames (MRFs), the panel zone region can significantly affect overall ductility and energy-dissipation capacity. This study investigates the influence of panel zone flexibility on the seismic response of steel MRFs by comparing two modeling approaches: one with a detailed panel zone representation and the other considering fixed beam-column connections. A total of 30 2D steel MRFs (15 frames incorporating panel zone modeling and 15 frames without panel zone modeling) are subjected to nonlinear time-history analyses using four suites of ground motions compatible with Eurocode 8 (EC8) soil types (A, B, C, and D). Structural performance is evaluated at three distinct performance levels, namely, damage limitation (DL), life safety (LS), and collapse prevention (CP), to capture a wide range of potential damage scenarios. Based on these analyses, the study provides information about the seismic response of these frames. Also, lower-bound, upper-bound, and mean values of behavior factor (q) for each soil type and performance level are displayed, offering insight into how panel zone flexibility can alter a frame's inelastic response under seismic loading. The results indicate that neglecting panel zone action leads to an artificial increase in frame stiffness, resulting in higher base shear estimates and an overestimation of the seismic behavior factor. This unrealistically increased behavior factor can compromise the accuracy of the seismic design, even though it appears conservative. In contrast, including panel zone flexibility provides a more realistic depiction of how forces and deformations develop across the structure. Consequently, proper modeling of the panel zone supports both safety and cost-effectiveness under strong earthquake events.