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.

Under the offshore environment, RC structures in service experience rebar corrosion due to chloride ion penetration, and their seismic resilience is progressively weakened as service time increases. To investigate the effects of replaceable friction dampers and FRP bars on the life cycle seismic resilience of RC frame-shear wall structures, this paper examines conventional RC frame-shear wall (RCF-SW) structures and RC frame-FRP hybrid reinforced shear wall structures with replaceable friction dampers (RCF-FRSW-FD). The seismic responses of these structures at 0, 35 and 55 years of service are discussed based on the incremental dynamic analysis (IDA) method. Meanwhile, post-earthquake resilience indicators (repair cost, repair time, and casualties) of the two structures are systematically analyzed using the FEMA P-58 theoretical framework. The results show that, as service time increases, structural damage and repair costs rise significantly, repair time is prolonged, and overall resilience declines. Furthermore, the greater the ground shaking intensity, the more pronounced the impact of corrosion on structural deterioration. Compared with the RCF-SW structure, the shear wall employing the replaceable friction dampers and FRP bars can significantly reduce the seismic response and damage probability of the frame-shear wall structure. This combination also effectively enhances the seismic resilience of the structure throughout its life cycle.

Structural seismic response monitoring plays a crucial role in the earthquake damage assessment and evaluation of seismic resilience for urban building clusters. Addressing the issues of high cost and low prevalence of existing seismic sensors, this paper proposes a structural seismic response monitoring system based on surveillance cameras. The system develops a hierarchical line segment descriptor matching algorithm for building structures and introduces a time-history data extraction technique for structural seismic displacement responses based on line matching. This effectively resolves the challenge of targetless structural surfaces and indistinct natural feature points in real earthquake scenarios. Thereby, enabling real-time monitoring of inter-story drift at a sub-pixel level. The system has been successfully demonstrated in the world's first practical earthquake visual monitoring application at a middle school in Sichuan Province. The results show that even under complex and varying lighting conditions at night, the monitoring system maintains high accuracy, achieving sub-pixel-level inter-story drift monitoring with peak inter-story drift errors within 35% and structural natural frequency errors within 5%. Furthermore, the monitoring system adopts a lightweight design, with resource utilization rates of both the central processing unit (CPU) and graphics processing unit (GPU) below 15% when processing a single surveillance video, meeting the requirements for real-time multi-node processing and ensuring efficient system operation. Compared to traditional accelerometer solutions, the visual monitoring system eliminates the need for additional dedicated sensors, leveraging existing security surveillance equipment to construct a building cluster monitoring network. This approach not only enables dual-purpose use of existing surveillance cameras for both routine and emergency scenarios but also provides a new technological approach for seismic monitoring of urban building clusters.

Ground motions caused by seismic waves propagating to the near surface due to the rupture of an uncertain seismic source also have uncertainty. In this paper, the uncertainties of asperity intensity and rupture velocity are represented by random variables, and three rupture scenarios are set up to consider the uncertainties of asperity location and initial rupture location. The spatial distribution of ground motion parameters in the valley near a dip-slip fault with uncertainty is investigated. The influences of the fault distance and the dip angle on the uncertainty of the ground motion parameters in the valley are analyzed. The multiplicative dimensional reduction method is used to improve the computational efficiency of the uncertainty quantification problem, and the physical process from fault rupture to site response is simulated based on the boundary element method. The results reveal that the uncertainty of seismic source leads to the uncertainty of ground motions. The scattering of seismic waves by the valley leads to the non-uniform amplification of the uncertainty. The coefficient of variation (COV) of the peak acceleration of the vertical ground motion at the center of the valley can reach 0.27. There are violent fluctuations in the spatial distribution of the COVs of the peak velocities of the vertical ground motions of the mountains. The variability of the ground motion at the valley decreases with the increase of the fault distance, and it tends to stabilize when the fault distance is greater than 4 km. The variability decreases with the increase of the fault dip angle, and the maximum variability of the peak ground acceleration can be up to 4 times the COV of the asperity intensity.

The duration of ground motion can significantly influence the cumulative damage and failure levels of structures, but its impact on structural response is inadequately considered in current seismic design. To explore the effect of ground motion duration on structural damage, this study employs a spectral matching method combined with wavelet transform to select 115 ground motion records of varying durations from the Japan strong-motion database (K-NET). Earthquake damage spectra under two different restoring force models were calculated, and a comprehensive analysis was conducted on the effects of ground motion duration, yield strength reduction factor, structural natural period and other factors on the structural damage spectrum. Additionally, 585 natural earthquake records of varying durations and different site conditions were selected from the Pacific Earthquake Engineering Research Center (PEER) database. Taking into account the combined influences of ground motion duration, yield strength reduction factor, structural restoring force model, and site conditions, a damage spectrum prediction model was developed using a differential evolution algorithm. Compared with existing prediction models, the proposed model reduces relative errors by more than 40%, which offers improved accuracy for predicting damage spectra that consider the effect of duration. The results of this study provide valuable insights for structural seismic design and damage assessment when considering the impact of ground motion duration.

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.

To improve the seismic performance of building structures and overcome the shortcomings of traditional passive tuned mass dampers (TMDs) with narrow vibration reduction frequency bands and difficulty in adjusting their own frequencies, a SMA-TMD with frequency modulation capability is presented based on SMA springs made of shape memory alloy (SMA) materials. Through frequency testing experiments, researchers found that the frequency of SMA-TMD increases with the increase of current flowing into the SMA spring. Shaking table tests were designed and conducted to validate the feasibility and effectiveness of the frequency tuning and vibration reduction performance of the SMA-TMD. The experimental results show that compared to a detuned traditional TMD, the SMA-TMD, which retunes with the main structure by adjusting input current, demonstrates a higher vibration reduction rate in controlling the top floor peak acceleration response of the structure. The damping performance can be improved by at least 21.5%. Furthermore, the working stroke of the SMA-TMD is significantly improved compared to that of the traditional TMD, the maximum working stroke under the two sets of experimental conditions can be reduced by at least 46.9% and 39.2%, respectively. This improvement can save installation space, reserve more building area, and broaden the application scenarios by enabling placement in structures with spatial limitations.

This study investigates the influence of ground motion duration on the damping reduction factor through response spectrum analysis of single-degree-of-freedom systems with various damping ratio levels. The significant duration (D_S5-95) is chosen as the measure for ground motion duration. By using 84 pairs of long-duration (LD) and short-duration (SD) spectrally equivalent records, the effect of ground motion duration is decoupled from the acceleration spectral shape. The average damping reduction factors for the LD and SD sets are calculated within the range of natural periods from 0 to 6 seconds at different damping ratio levels. The effects of damping ratio, natural period, and D_S5-95 on the damping reduction factor are quantitatively analyzed. A nonlinear regression model is proposed to account for the influence of ground motion duration on the damping reduction factor, with the regression parameters provided. The results indicate that, for a linear single-degree-of-freedom system, the influence of ground motion duration on the damping reduction factor depends on the natural period and damping ratio. In the short-period range, D_S5-95 has no significant effect on the damping reduction factor、However, in the long-period range, the damping reduction factor tends to decrease as D_S5-95 increases.

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.

Existing studies have shown that near-fault impulsive ground motions have a significant impact on the seismic performance of concrete gravity dams. However, current research on the vulnerability of concrete gravity dams under near-fault ground motions remains limited, and most studies use a single response parameter as the performance indicator, which makes it difficult to comprehensively characterize the seismic performance of gravity dams. Taking a certain engineering concrete gravity dam as an example, this paper establishes a unified plastic damage model of the dam-foundation system. Multiple measured near-fault impulsive and non-impulsive ground motions are selected. Then, it calculates the comprehensive damage index of the gravity dam is calculated using the method of efficacy coefficient combined with the modified weighting model. A logarithmic probability seismic demand model is established for PGA (peak ground acceleration) and three single indices including accumulated base sliding, relative displacement of the dam crest, and overall damage index, as well as a comprehensive response index. By combining the criteria for dividing damage levels for each index, vulnerability curves are obtained. The paper compares the characteristics of near-fault ground motion pulses and the influence of single and comprehensive response indices on the seismic performance of concrete gravity dams. The results indicate that the probability of concrete gravity dams experiencing minor, moderate, and severe damage under near-fault impulsive ground motions is higher than that under non-impulsive ground motions. Evaluating seismic performance using a single index may lead to overestimation of the dam's seismic resistance under certain PGAs. Using a comprehensive damage index as the performance indicator for evaluating the probability of damage and ultimate seismic capacity of gravity dams is more reasonable.