In response to the current inability of the strong-motion observation network to provide seismic input records covering all areas of the epicenter vicinity, a technical framework for the rapid generation of kilometer-grid strong motion time histories has been established. Taking the M_S6.8 earthquake in Dingri, Xizang on January 7, 2025, as an example, the detailed processes of each technical procedure are described, and work on the inversion of the source rupture process, estimation of regional site conditions, and simulation of strong motion time histories has been carried out. The following results are obtained. The earthquake released a seismic moment of 4.7×10¹⁹ N•m, corresponding to a moment magnitude of 7.05. The fault slip is predominantly normal with a small amount of left-lateral strike-slip component, and the maximum slip displacement exceeded 3 meters. The rupture lasted for more than 20 seconds, mainly propagating in the northward direction, which may cause potential directivity effects. A V_S30 distribution map and engineering site classification map with a resolution of 30 arcseconds are provided, and the sites in the vicinity of epicenter area are mainly classified as ClassⅠand ClassⅡ, with V_S30 values ranging from 260 m/s to 510 m/s in the majority of the southeast area. Simulated three-component acceleration time histories for 14 996 virtual observation points in the near-field area (27°30′N~30°00′N、86°18′E~88°36′E) are provided, and the accuracy of the simulation results is verified by actual observation records. The maximum horizontal peak ground acceleration(PGA) can reach 1.0 g, and the 0.4 g and 0.2 g isolines approximately coincide with the IX and Ⅷ isoseismals, while the 0.10 g and 0.05 g isolines enclose areas slightly smaller than the Ⅶ and Ⅵ isoseismal zones. This research work and its results can provide reasonable seismic input for the damage identification, disaster evaluation, and resilience assessment of various disaster-bearing bodies in the epicentral area.

On January 7, 2025, an earthquake of magnitude M_S6.8 struck Dingri County, Xizang Autonomous Region. In this paper, the near-field seismic wave field and instrumental intensity field were simulated using the strong ground motion simulation and prediction cloud platform of the Institute of Engineering Mechanics, China Earthquake Administration (CEA), combined with the kinematic seismic source model, the regional public velocity model and the digital elevation model. The simulated and measured instrumental seismic intensities are comparable at the stations of the National Seismic Intensity Rapid Reporting and Early Warning Project. The simulated high intensity zones are mainly distributed around the place of the surface projection fault, and the simulated instrumental seismic intensity field is basically the same as the survey seismic intensity field. On the basis, the earthquake damage to typical buildings (mainly earth/stone and wood structures) and casualties was evaluated and the evaluation results were also comparable to the actual data.

Buildings are essential fundamental for maintaining the economic, cultural, social, and functional aspects of urban life and are the basis for ensuring urban seismic resilience. The seismic resilience of buildings not only depends on the seismic capacity of structural components but also on non-structural components and equipment. Currently, there are no established methods for enhancing the seismic resilience of existing buildings. This paper outlines the basic approach for enhancing the seismic resilience of existing buildings, proposing methods aimed at ensuring structural safety, meeting predefined functional requirements, and enabling rapid recovery. The paper establishes seismic resilience enhancement objectives for existing buildings, considering both the function and the remaining service life of the buildings, and a “five-step” approach to enhancing seismic resilience is also developed. Finally, a case study of a specific building’s seismic resilience enhancement is presented to preliminarily verify the rationality and feasibility of the proposed methods. This paper can provide practical insights for enhancing the seismic resilience of buildings, as well as individual infrastructure components such as bridges and tunnels.

The main task of the building structure array is to record the failure process of civil engineering structures in detail, and to provide structural response information for many related studies such as seismic design, seismic damage assessment, and earthquake safety alarm. However, due to the constraints of economic cost, field testing technology and data processing level, it is unrealistic to deploy sensor monitoring equipment on all floors of the entire structure, so how to obtain the most complete structural information with the least number of sensors is the purpose of optimizing the layout of structural array sensors. Considering the advantages and disadvantages of the effective independent method and the modal kinetic energy method, a unit stiffness energy-driving point retention method was proposed, considering the advantages and disadvantages of the effective independent method and the modal kinetic energy method. In this method, the unit stiffness modal energy is used as the information matrix, and the principle of effective independence method is used to screen the measurement points, so as to ensure that the high-energy measurement points maintain linear independence to the greatest extent. Finally, taking a steel frame as an example, the proposed method, the effective independence method, the modal kinetic energy method and the unit stiffness method are used to lay the sensors on the model respectively, and the modal assurance criterion and the Fisher information matrix criterion are used to evaluate the layout results of the four methods. The results show that, compared with the other three methods, the proposed method has the least number of sensors when the mode vectors are linearly independent, and the proposed method can obtain the most modal information with the same number of sensors.

Clutching inerter damper (CID) has been extensively studied in structural vibration control recently. Because the passive CID device does not take into account flywheel speed reset and cannot achieve an ideal piecewise model, its control performance is limited. Therefore, this study explores the semi-active implementation of the ideal CID model. This paper begins with a comparative study of the ideal and passive analytical models of CID, providing insight into the performance differences and limitations of the two models. Subsequently, an electromechanical clutching inerter damper (ECID) scheme is proposed, which includes energy harvesting and variable inertance. The implementation of the electrical inertance, flywheel speed reset, and energy recovery functions are also discussed, and an electromechanical hybrid simulation model of the ECID is established. This paper thoroughly examines the control and energy recovery performance of the ECID through theoretical and simulation analyses. It explores the effects of resistance and capacitance in the ECID circuit on system performance and demonstrates that the ECID has significant vibration control and energy recovery capabilities. This study presents a comprehensive scheme for the implementation of CID, variable inertance, and energy recovery, which has theoretical reference significance for the development of self-powered semi-active variable inertance devices.

Reducing the seismic acceleration response of nuclear containment and ensuring the safety of nuclear power equipment under strong earthquakes is of practical significance for improving the seismic toughness of nuclear containment. Tuned mass damper (TMD) can effectively reduce the wind vibration response, but it has the disadvantages of narrow frequency band and low damping efficiency for seismic response control. By combining TMD with inertial volume, a tuned mass damper inerter (TMDI) is proposed to reduce the seismic acceleration of nuclear containment. Based on the performance requirement design idea and H_∞ optimization criterion, an optimal parameter design method for TMDI was established. On this basis, a numerical simulation method is developed by using the substructure idea combined with ABAQUS and Matlab, and the finite element simulation of the seismic response of nuclear containment under TMDI control is realized. The validity of the theoretical analysis is verified by the TMDI seismic control example of a finite element model of a nuclear containment. The results show that the peak acceleration absorption rate of the top of the nuclear containment is 46.1% when TMDI is used, and the tuning mass required when TMDI reaches the same damping index is reduced by 28.2%.

In order to limit the excessive relative displacement between pier and beam, a latticed long-stroke restrainer(LLSR) based on shape memory alloy (SMA) bar is proposed on the basis of single long-stroke shape memory alloy restrainer (LSR). The device consists of SMA alloy bar with excellent superelasticity and re-centering performance, MC nylon, steel pipes and strips or plates. SMA bars can consume ground motion energy and provide re-centering capability. The MC nylon and steel pipe form an anti-buckling system to prevent the SMA bar from buckling under pressure. Firstly, the structure and working mechanism of single long-stroke shape memory alloy damper and lattice long-stroke shape memory alloy damper are described. Secondly, the tensile test of SMA bars under different heat treatment temperature was carried out to determine the SMA bar with the best superelasticity, which was then used as the inner core of the LSR. Then, the axial tension and compression experiment of a single LSR was conducted to further study its mechanical properties. Finally, based on the experimental data of the LSR and the finite element software of ABAQUS, the numerical analysis and parameter analysis of the LLSR were carried out, and the corresponding design method was proposed according to the results of numerical analysis and parameter analysis. The research shows that LLSR not only has stable energy dissipation capacity but also has good re-centering ability.

A semi-active impact damper (SAID) with controllable timing is presented based on vibro-impact mechanism, aiming to control the multi-modal vibration of civil structures under earthquake excitations. The proper impact actuating force can interfere with the accumulation of structural vibration amplitude without additional controllable elements. In this paper, a device construction with adjustable collision clearance was proposed based on the SAID mechanical model and corresponding semi-active control strategy. The damping performance of the SAID system in a five-story frame structure is studied through shaking table tests. The results showed that the SAID system could effectively reduce the acceleration at the top floor of the structure and the inter-story drift. Time-frequency energy analysis revealed that the SAID system can transfer the structural vibration energy from low-order modes to high-order modes to accelerate the energy dissipation during the controlled impact process and suppress the structural response caused by dominant modes. An enhanced semi-active impact damper (ESAID) is further proposed to reduce the adverse effect of the acceleration sudden change caused by the impacts while improving the damping performance of the SAID system.

In order to predict the bearing capacity of steel plate-concrete reinforced composite (SPRC) coupling beams more conveniently. In this paper, it is of great significance to study the bearing capacity prediction model of SPRC coupling beams by machine learning (ML) method. Firstly, the SPRC coupling beam database is established by collecting the existing experimental data. On this basis, six ML algorithms, including extreme learning machine (ELM) algorithm, back propagation neural network (BPNN) algorithm, support vector machine (SVM) algorithm, K-nearest neighbor (KNN) algorithm, random forest (RF) algorithm and extreme gradient boosting (XGBoost) algorithm were used for data regression training. Through the comparative analysis of model performance indicators, it is found that the prediction model based on XGBoost algorithm has the best robustness and generalization ability. Compared with the softened strut-and-tie model (SSTM), it has higher calculation accuracy and stability. A high-precision SPRC coupling beam bearing capacity prediction model based on ML method is proposed. In addition, the sensitivity analysis of the parameters affecting the bearing capacity of SPRC coupling beams is also carried out. The results show that the influence degree of each characteristic parameter on the bearing capacity of SPRC coupling beams is in descending order as follows: steel plate ratio (ρ_p), coupling beam section height (h), coupling beam section width (b), span-depth ratio (l_n/h), stirrup yield strength (f_vy), longitudinal reinforcement ratio (ρ_s), longitudinal reinforcement yield strength (f_sy), stirrup ratio (ρ_t), steel plate yield strength (f_py), concrete compressive strength (f_cu).

Proton and heavy ion therapy facilities have garnered significant attention and widespread application in recent years due to their high-precision treatment capabilities. Hospitals are often located in urban areas with busy traffic, raising concerns about the potential impact of the road traffic environment on the normal operation of these planned high-precision devices. It necessitates a detailed feasibility assessment of the construction proposal for the project. This paper focuses on an actual engineering project, employing on-site real measurements to study the frequency characteristics of site vibrations induced by road traffic loads and the decay pattern of peak accelerations. A three-dimensional finite element model of the actual structure was developed to analyze the dynamic response of the proton and heavy ion therapy platform influenced by traffic conditions. The findings indicate that the vibrations generated by road traffic are primarily concentrated in the 5 Hz to 20 Hz range. High-frequency vibrations decay rapidly with distance. Peak accelerations of traffic loads at various distances from the road's centerline exhibit a multi-level amplification phenomenon, and in some areas, the peak acceleration may exceed that of the vibration source itself. Through 1/3 octave band analysis, the environmental vibration frequencies mainly affecting the central area of the proton and heavy ion facility range between 5 Hz to 20 Hz and 40 Hz to 60 Hz. Z-vibration level analysis shows that the platform's environmental vibration dynamic response meets the predefined standards for dynamic response design. This study provides a reference for the feasibility demonstration of construction plans considering the impact of traffic environments on facilities requiring high-precision equipment platform stability.

The dynamic response of compacted coarse-grained soil as a filling material for the surface layer of railway subgrade bedding is crucial for the overall performance of the subgrade structure under long-term cyclic train loads. This study conducted a series of cyclic triaxial tests to investigate the effects of fine content, confining pressure, and cyclic stress amplitude on the accumulated behavior of coarse-grained soils. The test results indicate that under the same cyclic loading conditions, specimens with higher fine content exhibit less accumulated axial strain. Furthermore, coarse-grained soil specimens exhibit less accumulated axial strain under higher confining pressure or lower cyclic stress amplitudes. Subsequently, the plastic shakedown limit of coarse-grained soils with different fine contents was determined based on a universal shakedown criterion. The results demonstrate that the plastic shakedown limit of coarse-grained soil specimens gradually increases with an increase in fine content. Under higher confining pressure, the corresponding plastic shakedown limit of coarse-grained soil is also higher. Additionally, by plotting the stress state corresponding to the plastic shakedown limit of coarse-grained soil on the plane of p-q, a relationship was established between the coefficient of fine content (FC) and the model parameters in the existing shakedown criterion. A united plastic shakedown criterion is then proposed for coarse-grained soils with different fine contents. The conclusions can provide a theoretical foundation for the design and stability assessment of railway subgrades.

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 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.

The Yellow River floodplain, covering an area of 250000 km² located in northern China, is a densely populated and economically developed region with a high level seismic background activity. In recent history, numerous earthquake-induced liquefactions occurred in this floodplain, however, relevant investigations and research are also lacking. So far, the knowledge of earthquake-induced liquefaction in the Yellow River floodplain is almost blank. In 2023, the Pingyuan M_S5.5 earthquake occurred in Shandong Province and induced soil liquefaction in the Yellow River floodplain. Through post-earthquake investigations, it is the first time that a case of real earthquake-induced liquefaction in the Yellow River floodplain has been analyzed in this paper. The characteristics of liquefaction induced by this earthquake have been obtained. The main points are as follows: this earthquake mainly induced soil liquefaction in silt and silty soils for 91% of sites in the total. The depth range of liquefied soil deposits is mainly of 7~12 m. The largest depth of liquefied soil deposit was confirmed at least 14 m, and possibly at an even deeper one. The depth of liquefied soil is beyond the common range of that in previous earthquakes. Liquefaction sites are mainly observed in the epicentral range of 6~12 km and are located in the seismic intensity 5 region and the boundary of intensity 6 region, which is significantly different from previous investigations. The abnormal distribution of liquefaction sites is closely related to the effect which is induced by the exclusive “highland-slope-lowland” microtopography in the Yellow River floodplain. In a moderate earthquake, the liquefaction in the Yellow River floodplain has induced moderate damage and has an especially different characteristic. It can be concluded that more severe liquefaction hazards may occur in large earthquakes. Therefore, it is urgent to develop a specific analysis procedure and evaluation method for soil liquefaction in the Yellow River floodplain. The work in this paper can improve the understanding of soil liquefaction during small and moderate earthquakes and provide firsthand information and new clues for research on soil liquefaction in the Yellow River floodplain.

To study the dynamic response characteristics of submarine sedimentary layer under seismic action, this paper establishes a single-layer unsaturated porous medium seabed model, presents its governing equations, boundary conditions and wave field expressions, and obtains the analytical solutions for the steady-state responses of unsaturated seabeds under different bottom permeability conditions. Through numerical examples, the influences of different bottom permeability conditions, saturation degrees, permeability coefficients, incident wave frequencies and depths on the solid surface displacement amplification factor and pore water pressure are analyzed, and the following main conclusions are drawn: under low-frequency conditions, the influence of the saturation degree of the sedimentary layer on the displacement amplification factor and pore water pressure is relatively weak. While in the case of increasing frequency, the influence of the saturation degree on the displacement amplification factor and pore water pressure is significantly enhanced. Under low-frequency conditions, for the sedimentary layer with a permeable bottom, the displacement amplification factor and pore water pressure are relatively large. While under high-frequency conditions, for the sedimentary layer with an impermeable bottom, the displacement amplification factor and pore water pressure are relatively large.

To clarify the degradation law of the mechanical property of 6061-T4 aluminum alloy after elevated temperatures as recommended by the GB 50429—2007 code for design of aluminium structures, a total of thirty-eight 6061-T4 aluminum alloy specimens were designed, and the unidirectional loading tests and cyclic tensile loading tests at room temperature and elevated temperature were performed. The effects of cooling type and loading protocol on the failure characteristics, initial elastic modulus, strength, stress degradation, and energy dissipation were evaluated. The experimental results show that the yield platform and strain hardening behavior in the unidirectional cyclic tensile stress-strain curve of 6061-T4 aluminum alloy were not observed. When the heating temperature was in the range of 100~300 ℃, the surface of 6061-T4 aluminum alloy specimens became slightly darker but not significantly. The surface condition of the 6061-T4 aluminum alloy can not be used as an indicator to evaluate the damage degree after fire. The temperature had a slight effect on the initial modulus of 6061-T4 aluminum alloy, and the cooling method also slightly affected the mechanical property of 6061-T4 aluminum alloy. When the temperature was below 200 ℃, the temperature did not have a significant effect on the strength of the aluminum alloy. When the temperature was above 200 ℃, the strength of 6061-T4 aluminum alloy exhibited a significant decreasing trend with the increase in temperature. During unidirectional cyclic tensile tests at room temperature, the yield strain of aluminum alloy specimens was slightly lower than that of unidirectional loaded specimens. Due to the plastic accumulation damage during the cyclic tensile process, the ductility of the specimens deteriorated under unidirectional cyclic loading. With the continuous increase in temperature, the yield of the specimens tended to occur earlier, and the deformation capacity changed from worse to better. The energy dissipation capacity of 6061-T4 aluminum alloy gradually decreased with the increase of temperature, and the cumulative energy was positively correlated to aluminum alloy strength and cycle number.

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 current seismic design codes for bridges primarily rely on design response spectra derived from far-field observational records, which fail to accurately reflect the ground motion characteristics and structural seismic response characteristics in near-fault regions. As a result, the seismic design for bridges in near-fault regions may be unsafe. To address the issue, near-fault ground motion time histories are selected from the Pacific Earthquake Engineering Research Center (PEER) database based on principles including source distance, moment magnitude, and peak ground acceleration(PGA). Average spectra are calculated using site foundation conditions and PGA as grouping principles, and then calibrated using a least-squares piecewise fitting method. This process yields statistical recommendations for three key parameters of the near-fault horizontal design gauge response spectrum: amplification factor, attenuation index, and characteristic period. Finally, adjustments were made to propose a gauge response spectrum that considers near-fault earthquake characteristics, providing a basis for incorporating near-fault ground motion effects into China's seismic design codes for bridges.

In this paper, it is proposed that the frame structure of glulam pillar and steel beam can address the issues of complex joint structure, limited beam stiffness and low lateral stiffness of long span glulam beam and column structure joints. Three joint specimens without planted bar and three joint specimens with the diameter of planting reinforcement as a variable were designed. Monotonic loading experiment were conducted on two joint specimens without reinforcement, while other joint specimens underwent low-cycle repeated loading to obtain their seismic performance, including failure mode, hysteresis curve, skeleton curve and energy dissipation capacity. The experimental results show that the measure of reinforced with planted bar can effectively improve the local bearing capacity of the transverse grain, the flexural stiffness and ultimate bearing capacity of the joints, but the increase in the diameter of the reinforcing bar has little impact. The energy dissipation capacity of the joint can be significantly improved by the measure of reinforced with planted bar, and the seismic performance of the joint can be improved. The failure modes of flexible end plate and rigid end plate are different, the members of the flexible end plates are S-shaped deformation and failure mode, the joint angle deformation is large, the bending stiffness is small, and the rigid end plate members are the transverse compression deformation and failure of the wooden column, and the bending stiffness and bearing capacity of the joint are strong. The formulas for the ultimate flexural bearing capacity of the joints are derived, and the theoretical values agree well with the measured ones.

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.

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.

Conical pipe joints are widely used in pipeline systems of various aerospace vehicles, and the stability of their sealing performance directly impacts the reliability of the aircraft's operation. Engineering experience has shown that setting circular grooves on the conical surface can improve the stability of the sealing performance of conical pipe joints. However, there is currently a shortage of experimental data to support this viewpoint. This article takes a 74° conical pipe joint commonly used in aircraft engines as the object and demonstrates rotational bending fatigue tests that circular grooves can significantly improve the stability of the sealing performance of conical pipe joints under vibration condition. On this basis, this article verifies through finite element simulation that the edges of the annular groove can generate contact pressure concentration bands, which serve as a form of line sealing. Thus, a qualitative explanation is provided for the mechanism of improving the stability of sealing performance by the annular groove. This study provides a reference for improving the design of conical pipe joints and other forms of static sealing structures.