In order to reveal the damage mechanism of ancient timber structures and to make a reasonable evaluation of the damage degree under earthquakes, this paper proposes a multi-scale seismic damage evolution analysis method for the ancient timber structure. Based on the generalized force-deformation relationship and performance-based seismic design, the generalized damage index is established through test data fitting analysis, thus multi-scale consistency damage indices are proposed. According to the multiple point constraint method (MPC), a multiple-scale model is developed for ancient timber structures, which can reveal macro mechanical properties and local failure details. The proposed damage evolution analysis method is validated by a cyclic loading test of mortise-tenon joint and a shaking table test of the multi-story timber framework, and the evolution process and results are also shown. The proposed multi-scale analysis method provides evaluation results of seismic appraisal for existing ancient timber structures, including assessments at the local material, component to overall structural levels. Furthermore, it elucidates the evolutionary relationships between each level of the whole structure, providing a scientific basis for reinforcement and repair work.

The slopes of hydropower projects in southwest China are high and steep and located in high seismic intensity regions. Consequently, there is a risk of earthquake-induced slope instability. Taking the drainage building intake slope of Lawa Hydropower Station at Jinsha River as an example, the dynamic finite element method is used to simulate the slope under rare strong seismic conditions. Based on this, an analysis of the slope dynamic response is conducted. Then, the post-earthquake slope deformation, stress and plastic zone distribution are studied. Finally, the dynamic stability of the slope below the spillway structure is evaluated using the dynamic strength reduction method, which reveals its potential instability mechanism. The results indicate that the acceleration response of the slope shows an elevation amplification effect, a surface amplification effect and a structural surface amplification effect. The slope undergoes the maximum permanent deformation of 10.2 mm after the earthquake, creating new local tensile stress zones and plastic zones. In rare seismic conditions, the safety factor of the potential sliding mass on the slope is 1.80, and its potential failure mechanism is deformation failure with fault JF1 as the rear boundary surface and rock mass at the slope toe shear damaged. This study can provide reference for the dynamic response and stability analysis of complex high and steep rock slopes with favorable-dipping faults under seismic action.

In order to study the mechanical properties of ultra-high performance concrete (UHPC)-reinforced damaged specimens, a total of 10 UHPC-reinforced damaged reinforced concrete beams were designed. These beams were subjected to a four-point bending performance test to study the crack development, damage pattern, load carrying capacity, and displacement of UHPC-reinforced reinforced concrete beams under bending. The effects of different reinforcement thicknesses and different reinforcement methods on the bending performance of UHPC-reinforced damaged RC beams were analyzed. The experimental study shows that the load carrying capacity of UHPC-reinforced damaged RC beams is greatly improved, and the ultimate load is improved by up to 194%.The number of cracks that occur when damage occurs is more than that of the original beams, and the development is more complete; the ductility is greatly improved compared with the original beams, and the displacement ductility coefficients of the reinforced beams are considered to be increased by 49.77%~178.31% compared with that of the original beams. The calculation method and basic assumptions of the ultimate load of the UHPC-reinforced concrete beams are proposed, and the test parameters are substituted into the formula. The results are more consistent with the test values, indicating that the proposed formula can effectively predict the ultimate load of such reinforced beams.

Environmental vibration is an important factor that affects the normal operation of various precision instruments and equipment. To solve the problem that the environmental vibration exceeds the vibration limit for the normal operation of equipment, the design of steel spring vibration isolation base is investigated. Through experimental verification and calculation analysis, the relationship between the vertical and horizontal stiffness of steel spring is derived, and the fuzzy problem of horizontal stiffness of steel spring is solved. A novel steel spring floating slab vibration isolation base is designed based on the requirements. The finite element method is utilized to study the vibration reduction and isolation effects of the pedestal under different steel spring stiffnesses. The deformation of the pedestal above the equipment with uneven mass distribution, the deformation of the pedestal with moving parts, and the vibration level of the pedestal are analyzed respectively. The analysis results show that the new steel spring floating slab vibration isolation base exhibits excellent horizontal and vertical vibration isolation effects. When the natural frequency of the base is 4.2 Hz, the maximum vibration reduction efficiency for the environmental vibration above 12 Hz can exceed 90%. The equipment with small moving parts on the base also demonstrates good stability. When the 50 kg moving parts move from one end of the base to the other, the vertical deformation of the base is less than 800 μm. When the disturbance force generated by equipment vibration is less than 1.5 kN, the base can still maintain the vibration level of VC-C. The research results can provide valuable references for the vibration isolation design of equipment in similar industrial plants.

The failure of porcelain cylindrical electrical equipment during earthquakes is a key factor contributing to power supply outages. The meticulous assessment of the seismic resistance of these devices is a foundational requirement for accurately gauging the overall seismic robustness of power systems. The judicious choice of the support dynamic magnification coefficient plays a crucial role in precisely appraising the seismic behavior of porcelain cylindrical electrical equipment. In this research, to derive the support dynamic magnification coefficients for these devices, vibration tests were carried out on three main types of porcelain cylindrical electrical installations: in cluding disconnect switches, voltage transformers, and current transformers, all of which were evaluated as integrated units with their respective support structures under various seismic excitations and different peak ground acceleration levels. Based on these empirical results, finite element analysis was used to examine the effect of parameters such as the stiffness of supports on the natural frequencies of the equipment-to-support system configurations. This analysis also included a discussion on how the support dynamic magnification coefficients vary with different periodic characteristics of the equipment-support assembly systems. The study findings indicate that, within the scope of this study, the support dynamic magnification coefficient tends to increase as the combined or overall period of the equipment-support system increases. Notably, when the total system period exceeds T_g, the seismic response of the system remains at a relatively high level, significantly exceeding the reference values set by design spectra and clearly surpassing the conservative 1.2 limit established by present guidelines, thus implying a potential underestimate of safety margins. Therefore, it is proposed that the support dynamic magnification coefficient for porcelain cylindrical electrical equipment should optimally not be less than 2.0, and concurrently, the frequency of the supports should not be belower than 30 Hz to ensure enhanced seismic safety measures.

The demountable reinforced concrete column-steel beam (RCS) combined frame consists of reinforced concrete columns, steel beams and demountable connectors. The beam-column joints are connected by bolted shear-resistant connectors, which can realize the disassembly of components for recycling and ensure the effective transfer of forces. However, the seismic performance of demountable RCS frame structure is still unclear, and there is an urgent need to conduct out research on the seismic performance of demountable RCS frame structure. To this end, for the proposed static test of non-demountable conventional RCS frame structure carried out by the team in the early stage, this paper adopts the finite element software ABAQUS to establish a finite element model, and compares the finite element calculation results with the test results through the damage modes, hysteresis curves, skeleton curves, and the cumulative energy dissipation, etc., to effectively verify the accuracy of the numerical simulation. With the help of the same finite element analysis method, a finite element model of the RCS frame with the new demountable connection was established, and the seismic performance of the RCS frame specimens under different node connections was studied in depth, including the force transfer paths, stress maps, hysteresis curves, skeleton curves, stiffness degradation, ductility, and energy dissipation, etc., and the feasibility of realizing the demountability of the frame structure is also analyzed. The results show that: the new demountable joints connection can control the plastic hinge in the region of the distal beam section, effectively protect the joints core area, and improve the ultimate load carrying capacity and stiffness. The hysteresis curve is fuller, slowing down the degradation rate of the load carrying capacity and stiffness, and greatly improving the frame's energy consumption capacity. The specimens with the new demountable joints connection can effectively ensure the continuity of the force transmission path, and its seismic performance indexes are significantly better than the traditional RCS frame structure. The research results and conclusions of this paper can provide a powerful design reference and data support for the seismic design of demountable RCS frame structures.

To identify an efficient and accurate feature selection algorithm for filtering seismic intensity indicators, the performance of four common feature selection algorithms, MIC, ReliefF, XGBoost and Lasso, was compared and analyzed. Based on the incremental dynamic analysis results of single-degree-of-freedom structures and the ground motion features, the feature selection regression model was established, the ground motion features was sorted and screened according to the Euclidean distance, the performance of the feature selection algorithm was evaluated according to the screening results, and the least squares regression model was established based on the incremental dynamic analysis results of the 2-storey, 4-storey, 8-storey and 12-storey reinforced concrete frame structures, and the standard deviation change of residual was used to measure the prediction ability of ground motion intensity measure selected by different feature selection algorithms for structural collapse. The results show that the accuracy of the ground motion features screened by the Lasso regression algorithm is 31% higher than that of other algorithms when used for structural collapse prediction. The results can be used as a feature selection algorithm reference for the selection of ground motion intensity measures in the uncertainty analysis of ground motion in the structural vulnerability analysis under the performance-based earthquake engineering (PBEE) framework, and can also be used as an effective feature selection algorithm reference for the selection of ground motion intensity measure s suitable for structural collapse prediction.

Due to process limitation, the laying accuracy of the traditional subway track bed is low, and the construction speed is slow, while the construction accuracy and efficiency of the prefabricated track bed are relatively high. In addition, many subway lines often require the addition of vibration reduction measures or an upgrade in the vibration reduction levels after a period of operation. Therefore, it is urgent to develop the prefabricated damping pad floating slab track (PDPFST) with various vibration reduction grades and convenient upgrade options for vibration reduction. Therefore, the PDPFST was developed and applied to three new metro lines in Qingdao. In this paper, the coupled simulation analysis and field tests were conducted on the dynamic performance and vibration reduction performance of the vehicle passing through the PDPFST. Firstly, the structure and construction technology of the PDPFST were introduced. Then, the requirements and evaluation methods for the simulation and test of dynamic performance analysis and vibration reduction effect analysis were presented. Then, a vehicle-floating slab track-tunnel coupled dynamic analysis model was established. Finally, the coupled simulation results were compared with the field test results. Through the above research, the following conclusions are drawn: Compared to the traditional track slabs, the construction progress of the PDPFST is increased by 3 times (approximately 110 meters per day). The simulation results of the dynamic performance and vibration reduction performance of the vehicle passing through the PDPFST are in good agreement with the measured values, and the dynamic performance of the vehicle meets the requirements. When the vibration frequency is greater than times the natural frequency, the floating slab track can exhibit a good vibration reduction effect. The vibration reduction effect of the PDPFST is remarkable. The high vibration reduction effect is approximately 13 dB and the medium vibration reduction effect is approximately 8 dB. The research results can provide a certain theoretical and practical reference for the design and implementation of the PDPFST.

To study the comfort level of human-induced vibration of a variable section steel-truss pedestrian bridge and the vibration reduction effect of tuned mass damper (TMD), a steel truss girder pedestrian bridge on the Beijing Hangzhou Grand Canal was taken as the research object. Finite element simulation and on-site measurement were used to study the human-induced vibration response of the steel truss pedestrian bridge. Based on the finite element model, the vibration response of the bridge before installation of TMD was analyzed, the pedestrian comfort level was determined, and the influence of pedestrian density, damping ratio and crowd excitation frequency on the bridge was discussed. In this way, the TMD design parameters were given, and the influence of TMD mass ratio on the vibration reduction effect was analyzed. On site measurements were conducted on the pedestrian bridge after the installation of TMD, and based on which acceleration time history and frequency spectrum analysis were used to study the human-induced vibration response of the bridge under corresponding operating conditions. Comparison of the results shows that before installing the TMD, the acceleration response of the bridge exceeds the specification limit, and the effect of human-induced vibration should be considered. In a certain range, the acceleration response increases with the increase of pedestrian density and decreases with the increase of damping ratio. The vibration response increases significantly when the pedestrian step frequency is close to a certain order of the vibration frequency of the bridge. After the installation of TMD, the measured human-induced vibration response of the bridge is reduced, and its response is consistent with the simulation results. The research results in this paper can provide theoretical support for the study of human-induced vibration of variable section steel truss bridge.

On December 18, 2023, a M_s6.2 earthquake occurred in Jishishan County, Gansu Province, affecting 118 towns including Dahejia Town, Liuji Town and Shiyuan Town. The areas have a relatively low level of economic development, with widespread and severely damaged brick (earth) and wood structures, resulting a significant number of casualties. In view of the large stock of brick-wood buildings in the region and their local characteristics, this study summarizes the architectural and structural characteristics of double-slope brick-wood structures and single-slope high wall brick-wood structures based on the on-site research, analyzes the typical earthquake damage phenomena and mechanisms, discusses the seismic vulnerabilities of existing brick-wood structures, and proposes the corresponding improvement measures in combination with the actual needs of rural construction. The findings indicate that in the epicentral area, most of the brick-wood structures are moderately damaged or severely damaged, and a few are destroyed. Structures with a mix of brick column and earth wall load-bearing and single-slope high-wall structures suffered more severe damage compared to double-slope brick-wood structures. The damage can be classified into four categories including overall or partial collapse, roof damage, wall damage, and other damage. The primary causes of the damage are identified as irrational structural systems, low mortar strength, poor overall integrity, and the absence of effective seismic construction measures. Consequently, this paper suggests targeted improvement measures to enhance the overall integrity, increase the collapse resistance of the walls, and prevent the collapse of roof components. These measures aim to provide a scientific basis and practical guidance for improving the seismic resilience of rural dwellings and optimizing disaster prevention and mitigation strategies.