To study the vibration influence of urban rail transit on buildings along the line, a frame-shear wall structure near a subway was selected as the research object. Under the excitation of rail transit vehicles, vibration monitoring of typical buildings was carried out at the foundation, along the height direction and the horizontal direction of the building, and the evaluation criteria such as 1/3 octave plumb vibration acceleration level, peak acceleration, and plumb fourth power vibration dose value were used for the analysis. The research results indicate that when the structure is 55 meters away from the inner contour of the tunnel, significant subway-induced vibration can still be detected inside the structure, and the relevant evaluation values may exceed the regulatory limits. In addition, the existing regulations do not specify the selection criteria for subway vibration, and the evaluation quantities determined by different value methods may seriously underestimate the impact of subway-induced vibration. Along the height direction of the structure, the vertical vibration response of the measurement points from the first underground level to the third above ground level did not significantly decrease, and there may be amplification at the top. The vertical vibration at the center of the floor slab is significantly amplified compared to the edge of the floor slab. The plumb fourth power vibration dose value at the center of the slab can reach 345% of that at the corner of the slab, and the corresponding maximum vertical vibration acceleration level can increase by 12.9 dB.

The compressibility of reservoir water and the influence of reservoir-bottom silt on the seismic response of the structure are taken into account to establish the high arch dam-reservoir water-foundation system model of Jinping-I Arch Dam, and the feasibility of using the acoustic-solid coupling method to simulate the effect of reservoir water on the dam body is verified by comparing it with the dynamic water pressure calculated by the Westergaard method. The absorption of silt deposited at the bottom of the upstream reservoir is simulated by different reflection coefficients of the reservoir bottom set in the model; seismic records that conformed to the hydraulic code response spectrum were selected as input based on the site conditions, and the response values of dynamic water pressure at the arch crown beam of the concrete dam under the action of vertical-incidence earthquakes with different bottom reflection coefficients were analyzed and studied. The results showed that the magnitude of the bottom reflection coefficient has a significant effect on the dynamic water pressure results at the arch crown beam, and the dynamic water pressure results increase with the increase of the reflection coefficient, and the difference of the dynamic water pressure at the heel of the dam with adjacent reflection coefficients becomes larger.

In order to study the mechanical properties of prefabricated thin-walled piers connected by grouted sleeves and the overall seismic performance of the bridge, firstly, the damage morphology characteristics of a group of ordinary cast-in-place thin-walled piers and prefabricated thin-walled piers connected by grouted sleeves were investigated through the proposed quasi-static test, and the differences in the skeleton curves and hysteresis curves between the two types of piers were analysed by comparing and contrasting them. Then, based on ABAQUS platform and the test data of this paper, the numerical simulation of the grouted sleeve connected thin-walled piers is carried out. On this basis, a three-span continuous box girder bridge is selected as an example, the multi-scale finite element dynamic analysis model of the whole bridge is established, and 100 ground are selected for the nonlinear time-history analysis, and the differences in the time-history response of the bridge components and hysteresis curves of the bridges set up with different piers are studied. Finally, the seismic fragility curves of different members were established to analyse the damage characteristics of each member of two types of bridges. The test results show that the damage form of prefabricated thin-walled pier is bending and shear damage, the concrete in the sleeve area is intact, the plastic hinge region is transferred to above the sleeve cross-section, the overall ultimate bearing capacity is slightly increased, the hysteresis curve shape is relatively full, with good plastic deformation capacity, and the hysteresis performance of ordinary cast-in-place thin-walled piers is basically the same. The model can simulate the overall mechanical properties of prefabricated thin-walled piers. The time-history fluctuations of prefabricated thin-walled piers mainly occur in the middle period of earthquakes. The difference in maximum displacement and internal force response between the two types of bridge piers is about 5% and 10%, and the bearing response is less affected compared to the bridge pier. Prefabricated thin-walled pier bearings and blocks are easily damaged components, and abutment bearings and blocks are more easily damaged than bridge piers. Prefabricated thin-walled piers are more easily damaged than ordinary cast-in-place thin-walled piers, but the difference is small. Prefabricated bridge piers can basically achieve the design principle of equivalent cast-in-place.

To study the seismic response and lap length requirements of the simply-supported bridge across faults, an elastic-plastic analysis model of the simply-supported bridge was established. Through dynamic response analysis, elastic-plastic analysis and shear resistance analysis, the influence of slip effect of fault ground motion on the lap length requirement of simple supported beam bridge is studied, and the relation between the relative displacement of pier beam and the permanent displacement of ground before plastic hinge failure is discussed. Research shows that the location of the fault affected the seismic response of the structure, and the closer the fault structure is, the greater the earthquake impact will be. The slip impact effect of fault ground motion increased the seismic response of the structure. The maximum shear strength ratio of the plastic joint area of the pier under fault earthquake action is 0.47. The checking calculation of the shear strength of the pier meets the requirements of the seismic design code. The seismic response of the structure under cross-fault seismic action drifted, resulting in the plastic hinge only developing in the same direction. The residual sum of squares and R² of the polynomial fit are 539.910 and 0.984, respectively. When the permanent displacement of ground is 1.6 m, the relative displacement of pier and beam before plastic hinge failure is 49.5 cm, accounting for about 56% of the calculated supported length. When the peak acceleration is small, the supported length of the simply-supported beam bridge under the earthquake action across the fault meets the requirements of the code.

This paper presents a novel type of replaceable shear link with a variable cross-section. The proposed design involves expanding the cross-sectional area and employing fully bolted connections to the non-energy-dissipating components. This design approach not only facilitates the concentration of plastic deformation within the energy-dissipating region but also ensures easier implementation of elastic design due to the bolted connections. To assess the seismic performance of the variable cross-section replaceable link, three distinct section configurations were designed for cyclic loading tests: a low-yield-point (LYP160) specimen without weakening in the energy-dissipating region, a Q235 ordinary steel specimen with an opening in the energy-dissipating region, and an ordinary steel specimen with a long oval opening in the energy-dissipating region. Through the cyclic loading tests, the seismic performance of the replaceable shear link was examined thoroughly. The experimental results indicate that plastic deformation primarily occurs within the energy-dissipating region, with buckling and tearing observed around the openings in this region as the primary failure characteristics. The low-yield-point specimen exhibits an overstrength coefficient exceeding 3.0, featuring a complete hysteresis curve, superior energy dissipation capacity, and a plastic rotation of 0.18 rad. Although the specimen with elongated openings demonstrates significant overstrength coefficient and plastic deformation capacity, its energy dissipation capability is compromised due to the weakened section. The specimens with circular openings exhibit an initial elastic stiffness similar to that of the low-yield-point steel specimens, surpassing the stiffness of the specimens with elongated openings by approximately 84%. These findings provide valuable insights for applying variable cross-section replaceable links.

In order to study the seismic performance of ultra-high performance concrete filled high-strength square steel tube (UHPCFHST) columns, this paper uses the hoop factor, length-to-slender ratio, and axial compression ratio as the parameters of study to conduct the low cyclic reversed loading test. The damage patterns of the specimens were observed, and the influence of each parameter on the hysteretic properties, stiffness, ductility and energy dissipation capacity of the specimens was analyzed. The test results show that the damage characteristics of all specimens are similar, and the phenomena of steel pipe buckling and concrete crushing appear at the bottom of the column. With the increase of the hoop coefficient (from 0.55 to 0.98), the ductility of the specimens increased by 8.91% and 21.52%, respectively. The initial stiffness, horizontal bearing capacity and ductility of the specimens decrease with the increase of the length-to-slender ratio, and the greater the length-to-slender ratio, the more significant the weakening of the ductility of the specimens. When the axial compression ratio increases from 0.1 to 0.2, the initial stiffness and horizontal bearing capacity of the specimen increase, while the ductility decreases. At the same time, the load-bearing capacity test results in this paper and the calculated values of each specification are compared and analyzed. The calculation results of the United States ANSI/AISC 360—16 AISC specification for structural steel buildings are lower than the measured values by 48%, which is relatively conservative. The calculation results of the GB 50936—2014 technical code for cencrete filled steel tubular structures are higher than the measured values by 17%, After analyzing the Fujian provincial local standard DBT/T13-51—2010 technical specification for concrete-filled steel tube structures, the calculation is the most consistent with the actual measurement, which provides a reference basis for the design of high-strength square steel pipe ultra-high-performance concrete columns under low cyclic reversed loading.

The safety of cross-active fault tunnels poses a significant challenge in current railway engineering construction. Research on such tunnels primarily relies on numerical simulation. However, the refinement level of the finite element structural models used to analyze cross-fault tunnels is often inadequate, and it is difficult to accurately reflect the actual stress and deformation characteristics of the tunnel structure under fault displacement. The influence of invert-filling, railway track foundation, and steel rails are considered in this paper. Three tunnel structure models with different levels of refinement are established by using the finite element software ABAQUS, and the simplified and commonly used ring structure models are compared. The stress and deformation characteristics of the cross fault tunnel structure and its associated track system under the action of active reverse faults are analyzed in detail. The results indicate that the refinement level of the model significantly affects the stress levels and deformation calculation results of the tunnel structures. The longitudinal stiffness and integrity of the tunnel structure are strengthened when considering bottom filling layers and internal auxiliary structures, and the ability of the structure to resist fault is improved. Meanwhile, in light of the severe damage to tunnel tracks and ancillary facilities during the M6.9 earthquake in Menyuan, Qinghai, in 2022, a dedicated study is undertaken to further examine the mechanical behavior and deformation characteristics of tracks under strike-slip fault displacement. This analysis is based on a refined tunnel model, aiming to gain a deeper understanding of how tracks respond and deform under such geological forces.

Aiming to accurately differentiate between natural and non-natural earthquakes, a neural network model based on one-dimensional convolution and residual structures, named ResNet-1D, was constructed. This model automatically extracts features from three-component seismic records using convolutional layers with convolutional kernels of different lengths, pooling layers composed of max-pooling, and residual structures. The adaptive moment estimation method (Adams) is used to optimize parameters, and a linear discriminant function (Linear) is applied to distinguish between natural and non-natural earthquakes. Using 40000 velocity records of natural and non-natural earthquakes, compiled by the China Earthquake Networks Center from 2008 to 2020, the data was randomly divided into training, validation, and test datasets in a 6∶2∶2 ratio. The test results show that the classification accuracy for natural and non-natural earthquakes is 92.65% and 94.30%, respectively. Compared with traditional machine learning methods, the ResNet-1D model significantly improves the test results in terms of accuracy, precision, recall, and F1 score, effectively enhancing the accuracy of identifying natural and non-natural earthquakes. Moreover, variations in magnitude and epicentral distance also affect the classification accuracy of the model, with higher magnitudes and greater distances resulting in lower accuracy. The model proposed in this paper offers higher accuracy and provides technical support for accurately distinguishing between natural and non-natural earthquakes in seismic monitoring.

A rapid prediction method of seismic-induced damage in high-speed railway ballastless track simply-supported bridge system is proposed based on convolutional neural networks. To obtain more information of seismic motion, one-dimensional seismic motion data is transformed into three-dimensional image through continuous wavelet transform as the input of convolutional neural network. The reliability of the proposed method is validated by comparing with results in damage samples database. The influence of different hyperparameters of convolutional neural networks on prediction results and training duration are analyzed, and a combination of hyperparameters of convolutional neural networks optimized by Bayesian optimization is obtained. The time required for seismic analysis of high-speed railway ballastless track simply-supported bridge system using different seismic analysis methods is compared. The optimized convolutional neural network is utilized to predict seismic-induced damage of different key components in high-speed railway ballastless track simply-supported bridge system. The research indicates that the initial learning rate is the most significant factor affecting the accuracy of network prediction, while the learning rate decay factor, batch size, and number of training epochs have certain effects on the network prediction results. The training duration of convolutional neural network is mainly determined by the number of training epochs and batch size. The proposed method demonstrates high prediction accuracy for seismic-induced damage in various components of high-speed railway ballastless track simply-supported bridge system, and the network structure exhibits high applicability. The optimized convolutional neural network has shorter training time and more accurate prediction for seismic-induced damage in high-speed railway ballastless track simply-supported bridge system. The research findings can provide reference for rapid repair of seismic-induced damage in high-speed railway systems after earthquakes.

Infilled reinforced concrete (RC) frame structures are one of the most common structures. It is found that infilled walls have a significant impact on seismic performance of RC frames in past earthquake damage investigations and experimental tests. To accurately and rapidly assess seismic damage states of infilled RC frames after an earthquake, 660 infilled RC frames were firstly designed based on different building structure information (i.e. the seismic design intensity, constructed period, number of stories, story height, number of bays and the filling rate), then the non-linear time history analysis was performed for the 660 infilled RC frames with 10 ground motions in OpenSees. 6 600 data points were gained from the analysis, resulting in a dataset which was used to develop seismic damage state assessment models of infilled RC frames. Based on the dataset, nine machine learning models predicting seismic damage states of infilled RC frames were developed using naive Bayes (NB), K-nearest neighbors (KNN), decision tree (DT), artificial neural network (ANN), random forest (RF), adaptive boosting (AdaBoost), extreme gradient boosting (XGBoost), light gradient boosting machine ( LightGBM), category boosting (CatBoost) algorithms. The results indicated that CatBoost and RF models had the highest prediction accuracy for the seismic damage state which was 0.93 in testing dataset, followed by LightGBM and XGBoost models with an accuracy of exceeding 0.90. Compared with actual damage investigated in the past earthquakes indicating that RF and CatBoost models achieved an identical accuracy of 47%. However, the difference in the remain damage states within one damage state level occupied 76% for CatBoost model, which was higher than that of RF model. Based on the CatBoost, importance analysis was performed for different input variables. It is found that three input variables had the greatest impact on infilled RC frame, including seismic design intensity (SDI), peak ground velocity (PGV) and the spectral acceleration at S_a(0.4 s). Furthermore, the importance of the number of stories on the seismic damage state for infilled RC frames increased as the increase of the number of stories.