Based on the deficiencies of the generalized response displacement method and the integral response displacement method for longitudinal seismic analysis of the shield tunnel, the dynamic sub-str1cture analysis method for longitudinal seismic response of a large-diameter shield tunnel crossing the complex soil layer is proposed. The feasibility and superiority of the dynamic sub-structure analysis method are explored by comparing it with the calculation results of the three-dimensional (3D) soil-underground structure interaction model. Then, a finite element refined 3D model of the 2.7 km Suai submarine shield tunnel is established by using the proposed method, and the longitudinal seismic response of the large-diameter shield tunnel crossing complex soil layers is simulated and analyzed. The research results indicate that the proposed dynamic sub-structure method has clear concepts, accurate calculation results and high efficiency to simulate the dynamic soil-tunnel interaction, which can avoid the error effect of the equivalent soil spring used in the generalized response displacement method. At the same time, this method can consider the seismic effect of the complex soil layers which has been avoided by the generalized response displacement method and the integral response displacement method. Also, the calculation results by the proposed method can comprehensively present the typical earthquake damages of shield tunnels crossing the wide river valley or the strait. It proves that it is not appropriate to simplify the longitudinally of the shield tunnel into a straight line, as doing so would neglect the influence of the longitudinal slope of complex river valleys or the straits. Also, the longitudinal seismic response of the shield tunnel is more sensitive to low-frequency seismic waves and the bolts are more susceptible to seismic damage compared to the segment opening.

In seismic regions, many underground structures are inevitably partially embedded in liquefiable sites, which may cause complex seismic response mechanisms due to the varying distribution of liquefiable soil layers. This study investigates dynamic interaction between underground structures and liquefiable soils employing three-dimensional nonlinear finite element models. The seismic response of both standard and connection sections of the subway station-tunnel of underground structures in liquefiable sites is evaluated to reveal the seismic response patterns of the soil-structure system under different liquefiable soil distribution forms. The results revealed that compared to homogeneous liquefiable sites, liquefiable interlayer sites can cause greater seismic damage to underground structures, potentially leading to failure along the entire length of the subway station. Therefore, the post-earthquake failure modes of the structure and site should be comprehensively considered based on the site layers distribution characteristics.

This study investigates the application of machine learning (ML) algorithms for seismic damage classification of bridges supported by helical pile foundations in cohesive soils. While ML techniques have shown strong potential in seismic risk modeling, most prior research has focused on regression tasks or damage classification of overall bridge systems. The unique seismic behavior of foundation elements, particularly helical piles, remains unexplored. In this study, numerical data derived from finite element simulations are used to classify damage states for three key metrics: piers' drift, piles' ductility factor, and piles' settlement ratio. Several ML algorithms, including CatBoost, LightGBM, Random Forest, and traditional classifiers, are evaluated under original, oversampled, and undersampled datasets. Results show that CatBoost and LightGBM outperform other methods in accuracy and robustness, particularly under imbalanced data conditions. Oversampling improves classification for specific targets but introduces overfitting risks in others, while undersampling generally degrades model performance. This work addresses a significant gap in bridge risk assessment by combining advanced ML methods with a specialized foundation type, contributing to improved post-earthquake damage evaluation and infrastructure resilience.

The connection between subway stations and tunnels in subway systems is a critical consideration in the design of underground transportation systems. Expansion joints may be introduced between the station and tunnel to reduce the stress and deformation transmitted to the structure and mitigate the potential structural damage. However, adverse conditions such as large deformations in liquefiable sites and extreme earthquakes can severely impact the integrity of this connection. This study employs three-dimensional finite element numerical models of dynamic soil-structure interaction in liquefiable sites to investigate the seismic response of the subway station-tunnel connection structure under different distributions of liquefied soil layers and considering various structural connection methods. The results demonstrated that subway station-tunnel structure placed in liquefied interlayer sites experiences greater seismic damage compared to structures with their upper parts embedded in homogeneous liquefiable sites. In addition, using expansion joints between the station and tunnel can indeed reduce the seismic stresses and deformations transmitted to the structure, which can mitigate the extent and severity of its damage. However, the expansion joint can lead to misalignment between the subway station and the tunnel. The findings provide theoretical references for seismic design and disaster mitigation measures for subway structures in liquefiable sites.

An Ms 7.4 earthquake struck China Maduo County in 2021, and it was a typical strike-slip rupture earthquake with clear directionality. A near-fault bridge named the Yematan No.2 Bridge suffered severe seismic damage in the Maduo earthquake. To analyze the seismic damage mechanism of the Yematan No.2 Bridge, the detailed finite element model of the bridge upline and downline was established in this study. To analyze the coupled effects of soil liquefaction, traveling wave effects, and seismic inertial forces, and to make the numerical simulation results better reflect structural seismic responses under real-site liquefaction conditions, this paper proposes a simplified method for simulating ground motions in liquefiable sites. This method integrates key effects induced by liquefaction into the ground motion simulation process. The detailed finite element model of the bridge upline and downline was established in this study. Then, the near-fault seismic bedrock motion of three directional components was synthesized by using the velocity pulse method to simulate the low-frequency pulse component and the stochastic finite-fault method to simulate the high-frequency component. The seismic ground motion was inversely computed by the equivalent linear method, and the field residual displacement measurement was used to optimize the seismic ground motion amplitude. Furthermore, to study the soil liquefaction effect on the bridge seismic damage, a simplified model based on planar one-dimensional wave theory was employed, and the seismic ground motion on the soil liquefaction site was computed through the site transfer function by using the inverse Fourier transform. Finally, the bridge seismic response analysis was conducted under non-uniform seismic excitation to consider the seismic traveling wave effect. The results show that the bridge's severe seismic damage is caused by the following multiple factors: (i) the fault rupture directionality of the near-fault earthquake results in the significant girder displacement along the bridge; (ii) the differential displacements between the upline and downline are also attributed to the soil liquefaction effect; (iii) the seismic traveling wave effect of strong seismic motion exacerbates the bridge seismic damage.

This study focuses on the Yanmazhuang West Station and Jinan West Railway Station of Jinan Rail Transit Line 1, China, examining the dynamic characteristics of eight-layered silty clay and subway station responses in Jinan. Through shaking table model tests, including free-field, two-story two-span, and three-story three-span stations, it finds relationships between the silty clay's dynamic shear modulus ratio and strain, damping ratio and strain, and confining pressure and dynamic shear modulus. It also reveals soil and station structural seismic responses to different intensities and waves.

There are only a few worldwide cases where distant earthquakes have caused damage. One such example is the municipality of Centro located in Tabasco, Southeast Mexico, approximately 360 km from the Mesoamerican trench, where a strong ground shaking was felt during the M(w)8.2 earthquake of September 08, 2017. In this study, for 20 sites shear-wave velocity profiles were determined using Multichannel Analysis of Surface Wave and V-P profiles using Seismic Refraction techniques. Also V-S30 (shear-wave velocity up to a depth of 30 m) values were obtained for the same sites. The distribution of the V-S30 values in the study area varied from 120 m/s to 570 m/s and it was observed that sites where damage to buildings were reported lie near areas with V-S30 < 270 m/s. Additionally, the transfer functions of the 20 sites were estimated using the Thomson-Haskell method. The fundamental frequencies (f(0)) obtained through transfer functions had values varying from 0.9 <= f(0) <= 2.0 Hz. These transfer functions were convolved with the signal that represents the record in the bottom of the soil column in the study area to obtain synthetic accelerograms in the municipality of Centro. The only accelerograph station located in the study area (VHSA station) was used as a reference site. The horizontal-to-vertical spectral ratio of the VHSA location was used for site characterization to assess the effects of regional events. The study concludes that several factors contribute to the susceptibility of Centro municipality to distant seismic events. These factors include low shear-wave velocity (V-s), low fundamental frequency (f(0)), local site conditions, the presence of buildings on former lake zones, low seismic wave attenuation, and the regions' overall vulnerability to regional earthquakes.

The experimental approach is crucial for investigating the seismic performance and damage process of underground structures. Considering the shortcomings of the 1-g, centrifuge shaking table and monotonic displacement pushover tests, a large-scale cyclic displacement pushover test method is proposed based on the soilunderground structure dynamic interaction and seismic performance quantification system. Taking a twostory three-span subway station structure as the prototype, the cyclic displacement pushover test device was designed for a 1/7-scale multi-story subway station based on the seismic response characteristics of underground structures. The corresponding numerical simulations and experiments were conducted. Typical numerical results (including the seismic damage process, capacity curves of the structural columns, and strain response) and test results (the macroscopic phenomenon of structural damage development, strain response, and deformation response) are interpreted. The results show that the proposed cyclic displacement pushover test is better than the monotonic displacement pushover test, the damage process of the tested station structure conforms to the description of the inter-story drift ratio (IDR) quantification system of seismic performance. Meanwhile, the column has greater strain amplitudes than other components, and the column strain curves reach their peaks before other components. Furthermore, the tested station structure has a similar damage pattern to the Daikai subway station. The reliability and feasibility of the proposed cyclic displacement pushover test method are verified.

Seismic fragility analysis is a crucial tool for assessing the seismic performance of buildings. In areas with dense clusters of tall buildings, the significant site-city interaction (SCI) effect alters wave propagation mechanisms, influencing the seismic fragility of structures. However, a significant increase in computational workload results from the need for detailed modeling of sites and building clusters for the SCI analysis. To address this challenge, this work first investigates the minimum number of earthquake waves required to characterize SCI-induced response changes. The Central Business District of Shanghai is analyzed. A table for the recommended minimum number for a given accuracy requirement and prediction reliability is provided. Moreover, a seismic fragility analysis method considering the SCI effect is proposed for low-rise buildings. The case study indicates that, buildings with similar height will exhibit various fragility changes after considering SCI. For the complete damage state, the mean intensity value of the fragility curve can be 14.4 % smaller than that without SCI. In addition, this approach provides significant computational workload reduction. For the case study, the computational workload of the proposed method is roughly 1/50 of that using traditional IDA method.

The influencing mechanism of the spatial variability in concrete materials on the seismic damage of concrete gravity dams is still unclear, and existing methods for evaluating the seismic damage are insufficient. In this work, the effects of concrete's spatial variability on the seismic damage distribution, energy dissipation, and deformation in concrete gravity dams are performed based on the damaged plastic model of concrete. Prior to the seismic damage analysis, the method for seismic inputting and the correlation function for realizing random fields of concrete materials are carefully determined. Based on the seismic damage analysis of the Koyna gravity dam, the tensile strength has the greatest influence on the seismic damage, followed by the elastic modulus and fracture energy. Aiming at the parameter of tensile strength, the decrease of correlation distance and the increase of the coefficient of variation increase the damage degree and complicate the damage distribution. A convenient and comprehensive damage profiling indicator is proposed to avoid the one-sidedness and evaluation error caused by using a single scalar damage value. The triangular area enclosed by the three individual damage indexes represents the comprehensive damage degree, and the shape change of the damage triangle indicates the change in the damage pattern of the dam. This damage profiling indicator is specifically designed to quantitatively distinguish and evaluate the damage degrees between a series of damage cases.