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.

To reveal the effect of P-Δ on the residual displacement ductility demand of structures, the damage-based residual displacement ductility demand ratio spectrum μ_res of single degree of freedom (SDOF) systems was conducted based on the Park-Ang damage model. The data were statistically processed to evaluate the effect of soil type, elastic stability coefficient θ, ultimate ductility coefficient μ_u and hysteretic model on damage-based μ_res. A prediction equation was proposed to estimate damage-based μ_res of SDOF systems through regression analysis. The differences of μ_res based on damage approach and ductility approach were compared and analyzed. Results show that the error in the estimation of damage-based μ_res when mean values along the earthquake population are considered without any soil distinction is inside 10%. When the P-Δ effect is not considered, the influence of μ_u on damage based μ_res exceeds 20%. When the P-Δ effect is considered, the influence of μ_u on damage based μ_res exceeds 50%. The ductility-based μ_res tend to be conservative compared to the damage-based ones. Finally, the prediction equation for the estimate of damage-based μ_res is proposed, which can be applied to the evaluation of residual displacement ductility demand ratio and seismic resilience.

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.

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.

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.

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.

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.

Following the M_S6.8 Dingri earthquake in Xizang, China, on January 7, 2025, extensive sand liquefaction phenomena were observed in Ⅷ~Ⅸ intensity zones, providing critical field data for studying liquefaction in high-altitude settings. This investigation employed field visits and surveys to explore the macroscopic characteristics, spatial distribution, and disaster-inducing mechanisms of liquefaction. Sand boils were documented in villages, embankments, floodplains, and lakeshore areas. The microscopic morphology and mineral composition of ejected materials were analyzed. Several recommendations for seismic liquefaction disaster prevention and mitigation are proposed. Key findings include the following. Sand boils predominantly occurred in river floodplains, lakeshores, and along roads, exhibiting circular, fissure, and beaded distribution patterns. Circular features measured 10~50 cm in diameter, while fissures spanned 14~30 cm in width and 85~100 m in length, distributing in sporadic or continuous clusters. No significant sand boils were observed in surveyed towns or villages. Two liquefaction sites of comparable size, distance and volume near the G219 national highway Gading line demonstrated contrasting damage levels: one section remained intact, while the other experienced severe subsidence, pavement collapse, and guardrail deformation. the characteristics of two sand boils feature in fissure and circular patterns. To bridge the gaps between liquefaction risk assessment and anti-liquefaction strategies, characterization and analysis of disaster-inducing mechanisms should be an essential research topic for the development of seismic liquefaction disaster prevention and control technology. The information and results of the investigation provide a reference for the understanding of seismic liquefaction mechanisms and informing post-disaster reconstruction and liquefaction disaster prevention.

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 Meta-analysis method will be used to comprehensively evaluate relevant literature on earthquake casualty estimation models, aiming to verify the effectiveness and reliability of existing models. Firstly, a systematic search will be conducted in both Chinese and English databases to select literature that includes information on sample size, evaluation factors, model types, and performance. Secondly, a random effects model is used to calculate the effect values included in the study, while the I² statistic is used to test the level of heterogeneity. Finally, the robustness of the Meta-analysis results is assessed through bias analysis and sensitivity analysis. The results indicate that the overall evaluation performance of the model is good, but there is significant heterogeneity and publication bias among studies, mainly due to methodological differences. Sensitivity analysis shows that the Meta-analysis results are robust. In summary, the overall evaluation effect of the earthquake casualty estimation models is reasonable and the model performance is good, which can meet the actual needs of earthquake emergency response.