The electric power system is the most critical component of urban infrastructure, serving as the foundation for the normal operation of a city. Earthquakes have a substantial impact on urban power systems. On one hand, it is reflected in the extensive damage to power infrastructure and the widespread power outages. On the other hand, it manifests in the long recovery times for power facilities and the significant impact on people’s livelihoods. Therefore, the performance analysis of the power system under seismic conditions and the post-earthquake restoration process urgently require attention. To more accurately assess and enhance the seismic resilience of urban power systems, a quantitative analysis framework for seismic resilience from a functional perspective has been established. The performance index of the power system is defined as the ratio of the population receiving power to the total population after an earthquake. The initial damage is determined through the seismic vulnerability modeling of power system components. The cascading failures of the power system following an earthquake are simulated using the DC power flow method to assess the power surplus in the city post-earthquake. The damaged components are then repaired, and the seismic resilience index is obtained by solving the system’s performance-time curve through an integral method. Based on functional analysis methods and component importance theory, the concept of post-earthquake restoration step length for the power system has been proposed. By adjusting the restoration step length, three restoration strategies have been developed including dynamic importance-based, static importance-based, and hybrid importance-based restoration strategies. A case study of a power grid in China has been conducted to validate the effectiveness of the resilience assessment framework and restoration strategies. The results show that the functional-based power system resilience assessment framework can effectively perform post-earthquake performance analysis and generate functional curves. The DC power flow analysis method accurately determines the state of each line and node in the power system, enabling a more realistic and reasonable simulation of cascading failures in the power system after an earthquake. Under 10,000 Monte Carlo simulations, the frequency distribution, average value, and the maximum value of the restoration strategy based on dynamic importance theory are significantly higher than those of the static importance-based strategy. The dynamic importance strategy yields the highest seismic resilience index, while the hybrid importance strategy provides intermediate results, and the static importance strategy results in the lowest seismic resilience index. The computational time required is inversely related to the resilience index, with the dynamic importance strategy taking 25 times longer than the static importance strategy. The hybrid importance strategy, which balances dynamic and static factors, has been shown to be the most efficient recovery strategy when dealing with large-scale computations and multiple scenarios, as it ensures higher resilience while maintaining computational efficiency.

The near-fault velocity pulse-like earthquake ground motions usually cause more severe damage to building structures. To analyze the seismic responses of the reticulated shells with seismically base-isolated substructures subjected to near-fault velocity pulse-like earthquake ground motions, three sets of ground motions are applied to a double-layer cylindrical steel reticulated shell supported by seismically base-isolated reinforced concrete frame structure. The first group consists of 22 near-fault velocity pulse-like ground motions with a distance of 5~10 km and a pulse period of 0.7~3.2 seconds, the second group includes 22 corresponding ground motions without velocity pulse, and the third group is based on the second group, considering the near field amplification coefficients given in GB/T 51408—2021 Standard for seismic isolation design of building. Through incremental dynamic analyses, the dynamic responses of the structure under the three groups of ground motions are compared. The results show that the velocity pulse has a significant amplification effect on the isolation layer displacements, the inter-story drifts, the axial forces, the base reaction forces of the reinforced concrete supporting structure, as well as the maximum nodal displacements and the member axial forces of the reticulated shell. Moreover, when only adjusting the intensity of the ground motions, the near field amplification coefficient can not effectively account for the influence of velocity pulse on the dynamic responses of the base-isolated reticulated shell with supporting structure. The conclusions of this study can provide a basis for the seismic isolation design of the base-isolated reticulated shell-supporting structure in high seismic intensity areas near fault zones.

On January 7, 2025, a magnitude 6.8 earthquake struck the Dingri region of Xizang Autonomous Region, resulting in certain damage to bridge structures. Based on field investigations, this paper primarily documents the seismic damage observed at the following bridges: Bridge No.1 and Bridge No.2 on County Road Guoqu X222, the Zacun No.2 Bridge on G219 Gading Line, and the Jijiao Bridge in Sakya County. Furthermore, the failure causes of the seismic damage to structural components in each bridge are preliminarily analyzed by integrating information such as the positional relationship between the main fault and the bridges, and ground motion records from seismic stations. The bridges damaged in this earthquake were predominantly of hollow slab girder structures, with the seismic damage primarily manifesting as minor destruction. Key observations include severe damage to the slope protection of abutments, lateral displacement of main girders without failure of the restraining block, and multiple instances of cracking or crushing in the bearing pedestals. Finally, this paper summarizes the lessons and techinical insights that are of practical guiding value.

In order to explore the specific causes of fastener bolt looseness and elastic strip loosening on the already built and operational rail transit lines, and to prevent similar problems from recurring on newly-built rail transit lines, this study combines with the actual situation of two rail transit elevated bridges in a certain city. Taking the failure analysis of U-beam fasteners as the breakthrough point, it explores the causes of fastener failure of ballastless track through field tests and vehicle-bridge coupling vibration simulation methods. Then, focusing on the vibration characteristics of the ladder sleeper structure and the comparison of vibration reduction and isolation effects between damper fasteners and the ladder sleeper structure, and applying the principles and methods of dynamic flexibility and energy flow, it analyzes the mechanism of factors affecting the vibration frequency of the track structure through a series of diagrams, and interprets the vibration mechanism of the track structure. The vibration effects are analyzed based on the measured and simulated data. The contribution of wheel wear to vibration is analyzed by measuring the vibration acceleration caused by vehicles in different operating years. Based on the field test, finite element simulation and vehicle-bridge coupling vibration calculation, the contribution of main girder section to vibration is analyzed. The contribution of track structure to vibration is analyzed by measuring the vibration acceleration of fasteners in different intervals; Based on the vibration field test of rail-crossing bridge, the mechanism analysis of the factors affecting the vibration frequency of rail structure is carried out with the vehicle-bridge-rail coupling vibration analysis program, and the vibration variation law is explored when the stiffness of fasteners and the stiffness of under-pillow damping pads are changed. The research results show that wheel wear, bending-torsion coupling effect of beam and vibration isolation of ladder sleeper are important potential factors that constitute fastener diseases of rail transit lines. The vibration reduction and isolation effect of ladder sleeper track structure is good, and the vibration of rail and ladder sleeper is significantly affected by the stiffness of fastener, while the vibration of bridge is significantly affected by the stiffness of damping pad. Proper reduction of fastener stiffness can significantly reduce the vibration of ladder sleeper. The research results can provide a reliable basis for improving the vibration research of rail transit bridge fastener system and provide design reference for related projects.

The M_S6.8 Dingri earthquake in Xizang on January 7, 2025, caused extensive building collapses and significant casualties. To investigate the causes of seismic damage, this study analyzed the amplitude-frequency characteristics and propagation attenuation characteristics of near-field ground motions using 35 sets of strong motion records obtained from the National Intensity Rapid Reporting and Early Warning Network. Through comparative analysis with the seismic ground motion prediction model (ZYLW22 model) for southwestern China, it was found that the measured values of near-field ground motion parameters (including peak ground acceleration and response spectra) were found to be slightly lower than the model predictions, while far-field observations exhibited higher values than predicted. Spectral analysis revealed a pronounced high-frequency energy dominance in the 1.0~3.0 Hz range within high-intensity zones of the earthquake. The epicentral region of the Dingri earthquake lies in a pastoral-agricultural area, where local buildings predominantly consist of self-built low-rise stone/wood or adobe structures and simple frame residential buildings. The earthquake disaster may be attributed to the poor structural integrity of these buildings, whose natural vibration periods closely match the predominant periods of ground motions, resulting in widespread structural failures. Additionally, the near-fault ground motions of the Dingri earthquake also exhibited source rupture directivity effects.

In this paper, a GPU-accelerated explicit nonlinear mode superposition method (ENMS) is proposed for real-time computation of large-scale bridge structures with local nonlinearities, especially non-linear dampers. This method treats the non-linear damping force as an external load, decouples linear equations of motion at each discretized time step by using the mode superposition method, and solves them by using an explicit step-by-step integration method. In this way, this method avoids the iterative solution to the equations of motion, and significantly improves computational efficiency with the fast mode superposition method. In view of the decoupled equations, a GPU is utilized to accelerate the computation, thereby further improving the computational efficiency. Numerical simulation studies on a large-span cable-stayed bridge show the followings: For a large multi-degree-of-freedom structure with local nonlinearities, this method can be used to conveniently and accurately solve dynamic responses with the parameters exported from Midas Civil. For an exponential Maxwell model of viscous dampers, the dichotomous method is able to accurately solve the damping force, providing a better solution to the problem of modeling non-linear dampers. The GPU acceleration can significantly improve the computational efficiency of the explicit non-linear mode superposition method.

Considering the 3D wave effect of soil and the kinematic soil-pile interaction, the seismic response of end-bearing single piles to vertically incident P-wave excitation is studied. The vertically incident P waves are modelled as the time-harmonic longitudinal displacement of the bedrock, and the governing equations of soil are established by considering both the longitudinal and radial displacements of the surrounding soil. The displacements of the surrounding soil are assumed as the summation of the free-field and scattered displacements, and subsequently the expression of the soil frictional force actingon the pile due to its motion is obtained. The pile is assumed to be a one-dimensional Euler bar. By substituting the soil frictional force into the governing equation of pile, the analytical solution of the seismic response of the pile under the action of vertically incident elastic P waves is obtained by considering the continuity conditions at the pile-soil interface and the boundary conditions at the top and bottom of the pile. The solution obtained is compared with existing studies to verify its validity. Finally, based on the obtained solutions, the effects of the main pile-soil parameters on the seismic amplification factor of the pile top, the kinematic response factor, the displacement of the pile, the frictional force of the soil and the kinematic Winkler parameters of the surrounding soil are investigated. The results show that: the resonance behavior of the pile-soil system occurs under the vertically incident P-waves, and the resonance behavior is particularly obvious at the first-order resonance frequency of soil layer. The pile slenderness ratio and pile-soil modulus ratio have significant effects on the seismic amplification factor of the pile top and kinematic response factor. The displacement of pile decreases significantly with the decrease of pile slenderness ratio or the increase of pile-soil modulus ratio. Compared with longer and softer piles, shorter and stiffer piles are subjected to a higher friction force of surrounding soil under seismic excitation. The influence of the pile slenderness ratio on the kinematic Winkler parameters is particularly prominent, and the kinematic Winkler parameters decrease significantly with the increase of the pile slenderness ratio, while the influence of the pile-soil modulus ratio is relatively small. The study can provide theoretical support for the seismic analysis and design of piles.

Ground motion parameters quantify the intensity of ground motion and their impact on building structures, making the selection of appropriate parameters crucial for pre-earthquake seismic design and post-earthquake damage assessment. Ground motion parameters and structural seismic responses are often statistically related through traditional correlation analysis and regression methods. However, data are mostly sourced from numerical simulations, which makes it difficult to capture the true nonlinear mapping relationship between the two. Therefore, this paper collected and organized nearly 1.28 million actual damage records from the Great East Japan Earthquake on March 11, 2011, and the complex mapping relationship between ground motion parameters and building damage levels was established based on four machine learning classification models, namely, XGBoost (eXtreme gradient boosting), RF(random forest), LightGBM (light gradient boosting machine), and CatBoost (categorical boosting). The SMOTE oversampling and Bayesian hyperparameter optimization algorithms were introduced to optimize the model, and the optimal combination of seven ground motion parameters was selected using two methods for evaluating feature importance. The results indicate that the XGBoost algorithm performs the best, with an overall accuracy of 71.39% on the test set. The optimal combination of ground motion parameters includs PGA, T_d, V_SI, PGD, PGV/PGA, PGV, and S_a. The amplitude, spectrum, and duration parameters of the ground motion show a strong correlation with post-earthquake building damage, while the cumulative energy parameters exhibit a weaker correlation. Finally, an earthquake loss prediction model based on the XGBoost algorithm was established using actual damage data from three earthquakes in New Zealand, validating the completeness, reliability, and regional generalization capability of the selected parameter combination. The research results can provide a theoretical basis and engineering reference for the seismic design of buildings and earthquake risk assessment.

The geotechnical isolation system based on glass beads and sand cushion (referred to as GSI-GBSC) has exhibited good seismic isolation performance on a one-story masonry building, but its effectiveness for two-story or higher rural buildings remains not determined. This study carried out a shake table test on a 1/4-scale model of a two-story masonry building. The first model was a two-story brick masonry structure without seismic isolation (the non-isolated model), and the second model was a two-story brick masonry structure equipped with the GSI-GBSC seismic isolation system (the isolated model). The acceleration and displacement responses of the two models were evaluated and compared, and compared with the results of the one-story rural building test conducted in previous studies. The results indicate that the glass-bead-sand-pad layer in the GSI-GBSC seismic isolation system tends to slip and slide, resulting in relative slippage between the foundation soil and upper structure of the isolated model. This ultimately reduces the seismic response of the upper structure. Under different peak acceleration input conditions, the upper structure of the isolated model was observed to move predominantly in a horizontal direction. In contrast, the displacement response of the non-isolated model increases as peak acceleration input values increase, leading to an increasing gap between horizontal displacement peaks in each layer. Furthermore, it was found that inter-story deformation in the isolation model is significantly reduced. Specifically, when peak acceleration input values are 0.2 g and 0.4 g respectively, it was observed that acceleration responses at top structures were 28% and 36% lower in comparison to those from non-isolated models. In summary, it can be concluded that while GSI-GBSC isolation system demonstrates good effects on one-story and two-story rural masonry structures, however, increasing weight and height-to-width ratio will reduce its effectiveness.

The freeze-thaw cycle (FTC) is one of a major factors leading to the damage of reinforced concrete (RC) structures in severely cold regions. The seismic performance evaluation of FTC-damaged RC beam-column connections is critical to the assessment of structural safety. However, the studies on the seismic performance evaluation of FTC-damaged RC beam-column connections under severe cold environments are still scarce. In this study, the influences of freeze-thaw cycles (N) and axial force ratio (n) on the seismic performance of RC beam-column connections are deeply investigated. Based on the test results, a calculation model of the shear force-strain envelope curve of RC connections that integrates the effects of the inhomogeneous temperature field distribution and axial compression ratio was established. The results show that with the increase of NFTC_s, the bearing capacity of the RC connections and the shear bearing capacity of the core area decrease, while the ductility, shear strain γ, and shear deformation to the total deformation Δ_PZ/Δ gradually increase, and after 300 freeze-thaw cycles, Δ_PZ/Δ is up to 21.90%. The established shear force-distortion calculation model for the FTC-damaged RC core area can accurately calculate the shear force V_jh and shear distortion γ. The mean error of both the shear force V_jh and shear distortion γ does not exceed 20%, and the standard deviation does not exceed 0.1. Furthermore, the precision of V_jh is slightly higher than that of γ. The shear skeleton curve calculation model established can be used to evaluate the seismic performance of FTC-damaged RC beam-column connections under earthquake actions.