Artificial boundaries are introduced to simulate the infinite domain in the analysis of soil-structure dynamic interaction, and the viscoelastic artificial boundary is one of the commonly used artificial boundaries. When the artificial boundary is used, the selection of the reference wave field as the input of seismic wave is very important, different reference wave field selection methods will lead to great differences in calculation accuracy. In this paper, four kinds of two-dimensional site models, including homogeneous half space, layered site, depressed terrain and underground structure are assumed. Then ANSYS finite element software and viscoelastic artificial boundary are used to simulate the above four site models considering SV wave vertical incidence and 30° oblique incidence. The calculation accuracy of three different reference wave fields is compared in detail. The results show that when the free wave field is selected as the reference wave field for all artificial boundaries of the soil-structure dynamic interaction calculation model, the accuracy of the calculation results is the highest.

This article mainly presents the investigation of bridges located in seismic intensity 8 degree and 7 degree zones on 306 Provincial Road, 310 National Road and Chuanting Highway. Peak acceleration of over 900 cm/s² was recorded at station GS. N0028 in the town of Dahejia, far exceeding the local rare earthquake fortification standard. However, the investigation results show that the bridges in the intensity 8 degree zone were mainly slightly damaged, including restrainer damage, lateral displacement of the main girder and bearing sliding, except for one bridge on Chuanting Highway where shear cracks were found in the pier, no other bridge in this area was found that suffered main structural damage. Bridges in the intensity 7 degree zone were basically intact, with some rubber deformations and unrecoverable displacements in the rubber bearings, as well as changes in the distance between restrainers. Fortunately, these issues did not affect their functionality. Concrete restrainer, as a measure to prevent lateral displacement of the main beam, has shown effectiveness in seismic damage, and is lack of rapid recovery characteristics. At the same time, the restrainer that installed cushion rubber pad also suffered severe damage, therefore, improving the cushioning device and considering the quick recovery of performance are needed in the future studies.

In order to study the vibration response of saturated foundation caused by train moving load under irregular track conditions, and further improve the vibration propagation and attenuation law of saturated foundation, the track irregularity load is introduced into the saturated foundation 2.5D finite element in this paper. The track irregularity load is transformed into frequency domain-wave number domain through Fourier transform, and the vibration response caused by the quasi-static load is compared and analyzed. The results indicate that when the vehicle speed is low, the vibration difference caused by the following two conditions is very small. As the vehicle speed increases, track irregularity significantly increases the amplitude of acceleration and displacement of saturated foundation, and the time-history curves show stronger fluctuation. Track irregularity has little influence on the acceleration spectrum at the center of the track. When the train runs at low speed and high speed, the frequency spectrum rules of the two loads are basically the same, and the main frequency distribution is basically the same. Under the condition of track irregularity, only the acceleration in each frequency band increases slightly. In addition, the pore water pressure of saturated foundation caused by high-speed railway will be greatly increased by track irregularity, and the pore water pressure decreases rapidly with the increase of depth.

An innovative amalgamation of the very short shear link (VSSL) and shear slotted bolted connection (SSBC), referred to as the VSSL-SSBC, ingeniously enhances the ductility and energy dissipation capacity of the VSSL, resulting in minimal damage. Consequently, the seismic resilience of eccentrically braced frames is markedly augmented. Cyclic loading tests were carried on a VSSL specimen, three VSSL-SSBC specimens with friction slip and a VSSL-SSBC specimen with ultimate deformation respectively, so the failure modes, hysteretic curves, bond curves and mechanical curves can be investigated. The experimental findings indicate that the mechanical property of the VSSL-SSBC exhibits a bifurcated developmental trajectory, characterized by initial stages involving friction slip within the SSBC and subsequent severe damage within the VSSL. Moreover, the ultimate bearing capacity and failure mechanisms of the VSSL-SSBC are observed to be congruent with those of the standalone VSSL. As for the mechanical curves, the VSSL exhibits distinct stages, encompassing elastic, elastic-plastic, and failure phases. In contrast, the SSBC is characterized by an initial elastic and subsequent slip phase. The VSSL-SSBC, a hybrid configuration, undergoes an extended sequence of elastic, slip, elastic-plastic, and failure stages. Notably, the deformation and damage of the VSSL within the VSSL-SSBC are significantly mitigated at equivalent displacements when compared to the standalone VSSL.Ultimately, the utilization of the finite element method (FEM) has been employed to corroborate the hysteretic curve and failure mechanisms with specimen VSSL-SSBC. The findings from the FEM simulations demonstrate a high degree of concordance with the experimental data.

Aiming at the demand of seismic protection of free-standing objects, a pendulum isolation device based on universal balls was developed. The structural characteristics and operation principle were introduced, and the design of an isolation device for protecting a pagoda could serve as a case study. Then the finite element software was used to analyze the bearing capacity between the universal ball and the disc. The accuracy of the damping mechanism analysis model was verified by tests. The isolation effect of the device under the eight-degree extremely rare earthquakes was analyzed by time history method, and was compared with the traditional friction pendulum. The results show that the isolation device not only has simple structure and reliable performance, but also has the characteristics of low friction coefficient, small acceleration threshold for triggering slip and flexibly adjustable damping mechanism. The carrying capacity of the node-to-surface contact can meet the design requirement. By means of viscous damper at one end, the damping mechanism shows obvious velocity correlation, and damping force increases with the increase of velocity. The device can achieve the isolation target while satisfying the displacement limit. Compared with the traditional type, when the displacement and acceleration response are limited, the device can achieve better comprehensive isolation effect under various seismic conditions by reasonably adjusting parameters of the damping mechanism.

A seismic damage investigation and analysis were conducted on the internal ceilings of public buildings in the 2023 M_s6.2 Jishishan earthquake. Three typical seismic damages, including the teaching building of Dahejia Middle School in Dahejia Town, Jishishan County, the outpatient building of Integrated Traditional Chinese and Western Medicine Hospital in Jishishan County, and the conference room of China Postal Bank in Jishishan County, were taken as examples to analyze the aluminum buckle plate ceilings that were less involved in previous investigations and study on typical seismic damage characteristics of aluminum buckle plate ceilings and indirect suspended ceilings, and some new seismic damage phenomena. Analysis suggests that aluminum buckle plates have sharp edges and corners, and the snap in connection requires a high level of flatness in the runner grid. If this type of ceiling is used in buildings with high seismic requirements or high personnel density, it is recommended to conduct specialized seismic analysis to avoid falling plates that may be harm to people or hinder their escape. In addition, in the assessment of seismic damage to suspended ceilings, in addition to the drop rate, factors such as deformation of the runner grid should also be considered. Furthermore, the reliability of the connection between the lighting units in the ceiling and the main structure should be strengthened to avoid a large number of falls during earthquakes. The analysis can provide reference for the seismic research and engineering application of suspended ceilings in public buildings.

The socket connection is convenient in construction and has a large tolerance error, but the durability is poor. In order to improve the construction quality and optimize the durability, we proposed a new type of assembled bridge pier tenon-socket prefabricated bridge per by combining the wet joint connection technology of ultra-high performance concrete (UHPC). One tenon-socket prefabricated bridge per specimen and one comparative pier specimen (integral cast-in-place bridge pier) were designed and fabricated. The damage mechanism and seismic performance of the assembled specimens were studied by using the proposed static test method combined with numerical simulation. The test results show that: the damage of both specimens is mainly ductile damage in the form of bending damage, mainly manifested by a large amount of concrete crushing and spalling in the plastic hinge area at the bottom of the pier, while the damage of the assembled joint and grout is smaller, and the residual deformation of the assembled specimen is only 79.09% of the overall cast-in-place specimen when the ultimate load is reached, indicating that UHPC grout can enhance the damage tolerance of the pier and make it easier to repair after earthquakes. The tenon-socket prefabricated specimens with short socket depth and lap length of reinforcement achieve reliable connection, and exhibit bearing capacity, ductility, energy dissipation capacity and stiffness close to those of cast-in-place piers under the same hysteretic displacement. With socket depth of 0.4D(D is the width of the specimen section) and above, the joints are reliably connected, and the integrity and seismic performance are basically equivalent to those of cast-in-place. Increasing the modulus of elasticity of grout has an improvement effect on the stiffness of piers. The influence of longitudinal reinforcement diameter on the seismic performance of bridge piers is more significant than that of lap reinforcement in the abutment. Increasing the reinforcement rate of longitudinal reinforcement improves the horizontal bearing capacity and energy dissipation capacity more obviously, but increases the residual deformation of bridge piers.

Due to the increasing requirements in seismic design codes and the performance deterioration of structures during the long-term service, seismic performance of existing buildings will no longer meet the design requirements. It is imperative to conduct seismic retrofit design. However, the current retrofit design method usually needs a large number of repeated iterations of nonlinear dynamic calculation, increasing the design difficulty and reducing its applicability. A performance-based seismic retrofit design method is proposed for the existing buildings based on energy balance, which is applicable for structural retrofitting with energy dissipation devices. It considers the performance target of multiple seismic levels without nonlinear dynamic calculation and few iterations during the design. A benchmark steel frame is retrofitted by the proposed method, and nonlinear dynamic analysis is performed to evaluate the performance of the original and retrofitted structures. The results show that the drift ratio of all floors is significantly reduced after retrofitting, and the average decreases for service level earthquake (SLE), design basis earthquake （DBE） and the maximum considered earthquake （MCE） are about 20%, indicating that the seismic performance is significantly improved by retrofitting. The inter-story drift ratios of the retrofitted structure under SLE, DBE and MCE are consistent with the design values, illustrating that the expected inter-story and roof drift ratio targets are achieved, which verifies the effectiveness of the proposed method. The damper designed by the proposed method remains elastic state overall during frequent earthquakes, and enters yielding state during DBE and MCE, realizing the expected energy dissipation mechanism. The ductility demand of the damper is evenly distributed along the height, which further indicates the rationality of the design method. The presented research can provide important reference to the seismic retrofitting design of the existing building structures.

A structural damage recognition framework based on a self-training semi-supervised neural network (SSNN) is proposed to solve the problem of insufficient labeled data in structural damage identification. The framework utilizes the multilayer perceptron (MLP) neural network for semi-supervised training by the self-training method. The data samples with high confidence are selected from the unlabeled data to make pseudo labels, expanding the training set. Normalized frequency change ratio and damage signature index are employed as input features of neural networks to identify structural damage. Firstly, the theory fundamentals of semi-supervised self-training learning are introduced. Secondly, the procedure of structural damage identification based on self-training semi-supervised learning, including neural network construction, damage characteristic extraction, and classifier evaluation, is introduced. Finally, the proposed damage identification method is illustrated by numerical simulation of a spatial truss and experimental data of a three-story frame. The results show that the self-training semi-supervised method can expand the labeled sample data by selecting samples with higher confidence from unlabeled data, thus providing sufficient labeled data for damage identification. Under the insufficient labeled data conditions, the SSNN performs better than MLP. Compared with MLP, SSNN increases the identification accuracy by 4% and 9% under the single and two positions damage locations, respectively.

The ground vibration input method based on viscous-spring boundary simulates the incidence of plane SV and P waves at different angles, and the acoustic structure coupling method is used to simulate the dynamic water pressure inside the lock chamber to study the seismic response of the lock roof displacement, acceleration and plastic damage in the ultra-high head lock chamber at different water depths. The study shows that when the seismic waves are obliquely incident, the seismic response of the ultra-high head locks varies significantly with the water depth compared to the vertical incidence, and the general degree of seismic response is greater than that of the vertical incidence. Under the same water depth conditions, the peak horizontal relative displacement and peak horizontal acceleration of the top of locks increases with the increases of the incidence angle in most cases. The seismic response of the lock chamber structure of the ultra-high head lock is significantly affected by the variation of the water depth. The area near the general gate wall with relative height of 0.2 is more likely to have serious damage, and when the relative water depth is 0.97, the tensile damage range on the waterfront side of the gate wall reaching serious damage is the largest. It is suggested that the combined effect of oblique incident seismic waves and different water depths within the gate should be considered.