The reactor building is a vital part of the nuclear island. Its floor response spectrum is essential for the design of internal equipment, such as the reactor pressure vessel and steam generator. To study the variation of the floor response spectrum of seismic isolation structures under different seismic inputs, a shaking table test was conducted on a nuclear reactor building model with a geometric similarity ratio of 1∶20. Three sets of seismic motions were generated based on NRC Reg. Guide 1.6. These included unidirectional (X-direction), bidirectional (X+Y directions), and triaxial (X+Y+Z directions) motions. Accelerometers were used to measure the floor responses under each condition, allowing for the analysis of response spectra for key floors. The results indicate that seismic isolation structures have two main peak points in the floor response spectrum, located near the first and second natural frequencies. The first frequency exhibits a lag, while the second frequency has a lead. There is a coupling effect between seismic motions in different directions. Near the first frequency, this coupling reduces the peak response of the upper structure’s floor spectrum. In contrast, near the second frequency, the interaction between vertical and horizontal seismic motions sharply amplifies the response, and this effect increases with height.

On December 18, 2023, the Jishi mountain earthquake revealed damage to 750 kV surge arresters. In order to improve the seismic performance of existing pillar-type electrical equipment in substations, the intermediate layer was selected as the isolation part for modification. Two intermediate isolation schemes were proposed: steel wire rope damper and composite seismic isolation bearing. The original surge arrester and isolation structure were modeled using the ABAQUS finite element method. Ten sets of seismic waves were input for finite element analysis, and the stress of bushing root, top acceleration and displacement responses of each structure were extracted to compare and analyze the isolation efficiency of the intermediate layer. The results show that under seismic action, the intermediate isolation structure of the steel wire rope damper can effectively reduce the stress of bushing root and top acceleration of the surge arrester, but it has a significant amplifying effect on the top displacement, which can easily cause wire tension damage. The intermediate isolation scheme with composite seismic isolation bearing can improve the vertical stiffness of the intermediate layer structure, so that the root stress and top acceleration of the original structure bushing decrease by more than 40%, and the peak displacement of the top is only increased by 12.56%, so as to achieve a good seismic isolation effect. The intermediate isolation device with composite seismic isolation bearings exhibits good seismic isolation efficiency and is an effective retrofit measure to improve the seismic performance of existing 750 kV surge arrester.

To address the significant discrepancy between damage degree and peak values when employing traditional acceleration indices for evaluating seismic damage in loess slopes under large earthquakes at far-field and small earthquakes at near-field scenarios, this study developed a novel evaluation system based on particle vibration velocity theory. Through shaking model tests and numerical simulations, the coupling mechanisms between acceleration and velocity responses during seismic damage evolution in loess slopes were systematically investigated, revealing intrinsic correlations between dynamic parameters and damage states. The results indicate the acceleration amplification effect of loess slopes is obvious. When the peak acceleration is taken as the evaluation index, the calculated intensity of loess slope top in the near field is greater than the actual intensity. A linear correlation was established between peak particle velocity and soil tensile strength. It is suggested that the peak velocity should be used as the evaluation index of failure intensity for loess slope with typical site amplification effect. An innovative five-level seismic intensity evaluation system was proposed in accordance with GB/T 17742—2020 specifications, defining velocity threshold intervals and characteristic failure patterns for each damage level, thereby establishing a quaternion correspondence criterion integrating damage degree, intensity, peak velocity, and seismic damage characteristics. This research provides theoretical foundations and quantitative criteria for seismic damage assessment of loess slopes.

To overcome the overly conservative nature of uniform hazard spectra and the unconservative nature of conditional mean spectra, the composite spectrum that combines the previous two spectra is proposed. The conditional periods are determined based on specific seismic information of the site (including magnitude, epicentral distance, etc.). This allows for the construction of multi-composite spectra that capture the regional seismic characteristics. A composite spectrum, representing the envelope of the corresponding conditional mean spectrum of one earthquake scenario, is ‘moderately’ conservative. By considering the influence of all earthquake scenarios in the region, the multiple mixed spectra are applicable for seismic analysis of all structures within the region. As illustrated by a specific region, the uniform hazard spectra, seismic parameters, and conditional periods of the region are determined following the seismic hazard analysis, and the method for generating multiple composite spectra is presented. Both the composite spectra and the design spectra are used to select actual ground motions. A case study is conducted on a typical cable-stayed bridge and the seismic responses in the longitudinal and transverse directions are compared. It shows that due to the contribution of higher modes, there exist significant differences in the vibration amplitude of different bridge components. The force response (including bending moments and shear forces) of the tower is more sensitive to short-period ground motions. Using design spectra to select ground motions significantly overestimates the longitudinal seismic response of the cable-stayed bridge. The overestimation is 50%, 23%, 38%, and 19% for the beam displacement, tower top displacement, tower base bending moment, and tower base shear force, respectively. It is suggested that the envelope of the mean seismic responses induced by the ground motions selected from each composite spectrum be used as the design seismic response of the cable-stayed bridge. This approach reasonably assesses the seismic demand of the bridge, thereby reducing the cost of the cable-stayed bridge and improving its economy.

A fully precast concrete energy-dissipation frame structure is proposed. It adopts straight threaded sleeve connections and employs viscous dampers to enhance its overall seismic performance. To investigate the seismic performance of the proposed precast concrete energy-dissipation frame structure, pseudo-dynamic tests were carried out on a precast concrete energy-dissipation frame specimen and a precast frame specimen. The research focused on the failure modes, plastic hinge development, hysteretic behaviors, stiffness degradation, ductility, and energy dissipation capacities of the frame specimens. The results indicate that both the precast frame specimens with and without viscous dampers experienced flexural-shear failure, with the damage concentrated near the mid-height of the column joint. Compared with the precast frame without a damper, the precast energy-dissipation framework exhibited a 97% increase in positive ultimate bearing capacity and an 82% increase in negative ultimate bearing capacity. The energy dissipation capacity and stiffness were also significantly improved. Considering the stress state of the framework, the precast framework columns are in a pure shear state at mid-height, which requires high shear resistance and is prone to brittle failure. Therefore, it is recommended to strengthen the shear resistance of the mid-height connection joints, improve the construction quality, and ensure the gripping force of the connection parts.

The Meta-analysis method will be used to comprehensively evaluate relevant literature on earthquake casualty estimation models, aiming to verify the effectiveness and reliability of existing models. Firstly, a systematic search will be conducted in both Chinese and English databases to select literature that includes information on sample size, evaluation factors, model types, and performance. Secondly, a random effects model is used to calculate the effect values included in the study, while the I² statistic is used to test the level of heterogeneity. Finally, the robustness of the Meta-analysis results is assessed through bias analysis and sensitivity analysis. The results indicate that the overall evaluation performance of the model is good, but there is significant heterogeneity and publication bias among studies, mainly due to methodological differences. Sensitivity analysis shows that the Meta-analysis results are robust. In summary, the overall evaluation effect of the earthquake casualty estimation models is reasonable and the model performance is good, which can meet the actual needs of earthquake emergency response.

Vertical ground motion is more intense in the near-fault zones, which poses a potential threat to the rocking self-centering (RSC) column piers with low seismic damage characteristics. Based on the OpenSees platform, finite element model of RSCs was established, and the accuracy of the modeling method was validated by comparing simulation results with pseudo-static and shaking table test results. Ten near-filed ground motions with pulse-like waves were used as the earthquake inputs, and bidirectional horizontal excitation and the three-dimensional excitation were considered respectively. A research on the influence of vertical ground motion on the seismic response of RSCs, and the continuous beam bridge with RSCs was conducted. The results show that vertical ground motions can increase the maximum axial force of RSCs, and reduce the minimum height of the RSC section, but the changes are not significant on average. Under disadvantageous conditions, the maximum axial force can increase by about 19.55%, and the minimum height of the compression zone of the section can be reduced by about 22.05%. Overall, the vertical ground motion has a minor impact on the maximum displacement at the top of RSCs. Vertical ground motion can greatly change the tensile stress and failure of energy-dissipating steel bars in RSC bridge columns. Therefore, it is necessary to consider the vertical ground motion effects on seismic response estimation of RSC bridge columns and RSC bridge structures.

In this paper, an innovative self-centering coupled shear link (SC-CSL) used between the steel brace and brace connection plate in the concentrically brace steel frame (CBF) is developed by combining the coupled shear link (CSL), shape memory alloy (SMA) bars and disc springs. Firstly, the hysteresis performance and failure mode of the SC-CSL are analyzed using the validated finite element method. Then, the seismic performances of CBF with a steel brace, CSL and SC-CSL are analyzed. Numerical results show that the innovative SC-CSL has excellent bearing capacity and low residual deformation. The SMA bars mainly sustain tension while the disc springs static under tension force, and the disc springs sustain compression while the SMA bars are static under compression force. The tension and compression forces of the SC-CSL can be almost equivalent with reasonable SMA bars and disc springs. In addition, the seismic performances of CBF, CBF-CSL and CBF-SC-CSL are almost the same, and no yielding or damage occurs to the steel beams, steel columns and steel braces during frequent earthquakes. The steel brace in the CBF has a severe buckling phenomenon. The CBLs with an elastic steel brace can have excellent bear capacity and deformation capacity. The residual deformation of CBF-SC-CSL visibly decreases during rare earthquakes, which shows good seismic performance and seismic resilience capacity.

A load-structure model for the underground interchange utility tunnel was established based on the response displacement method. Transverse seismic analysis was carried out on the underground interchange utility tunnel. The internal force, deformation, and damage responses of an underground cross interchange cast-in-place utility tunnel under seismic excitations along two main axes were analyzed. The results indicate that under major earthquakes, the inter-story displacement angle at the interchange node of the utility tunnel exceeds the standard limit by 167.50%, with tensile damage reaching 0.985, far exceeding the tensile damage limit, which marking it as the weakest part of the interchange utility tunnel. Due to significant differences in stiffness and deformation modes between the interchange node and standard segments, the deformation at joints near the interchange node is the greatest. Under major earthquakes, the deformation at the joints near the interchange node can be up to 20 mm and 18 mm in two directions, respectively. The maximum inter-story displacement angle between layers at the interchange node may not occur simultaneously. Under major earthquakes, the maximum inter-story displacement angle between layers exceeds that between the top and bottom slabs by 19.15%. Consequently, it is necessary to determine the most unfavorable condition based on the maximum inter-story displacement angle between layers. The findings can provide a reference for the transverse seismic design of interchange utility tunnels.

Progressive collapse is a nonlinear dynamic behavior of structural systems. In order to study the progressive collapse resistance laws of reinforced concrete planar frame structures after failure of important members, an important member identification method based on strain energy of members was proposed. The effectiveness of the method was verified by taking a four-bay and eight-story reinforced concrete frame structure as the target. It was found that the method identifies important members with high effectiveness. On this basis, eight reinforced concrete frame structures with different beam spans or total number of floors were designed in accordance with code. Firstly, important members were identified based on the above method and the adverse structural member removal scenarios were formulated. Then, impacts of different total number of floors and structural span on progressive collapse resistance capacity of reinforced concrete planar frame structures were analyzed by adopting the nonlinear dynamic alternate path method. Finally, the approximate functional curve of reinforced concrete planar frame structures between proportions of columns removed from ground floor and degrees of structural collapse was fitted. The results indicate that after removal of center column at ground floor, structures are mainly carrying vertical loads by ground floor frame beams, and frame beams of remaining floors cooperate with ground floor frame beams to support loads. The decrease in total number of floors and the decrease in span can increase redundant load carrying capacity of structures, which has a positive effect on resistance capacity of frame structures to progressive collapse. Frame beam span has a significant effect on degree of structural collapse and total number of floors has a limited effect on degree of structural collapse. The relationship between proportions of columns removed from ground floor and degrees of structural collapse of reinforced concrete plane frame structures can be approximated by a logistic function.