Xiuyun Zhu

Based on the structural and geological characteristics of the F1 weathering trough of a submarine tunnel and its spatial relationship with the cavern, a simplified calculation model of the weathering trough water inrush was established, and the formation, development process and influencing factors of the water inrush channel in the water-resistant rock layer were carried out by a numerical simulation of particle flow. It shows that the integrity and stability of the critical water-resistant rock mass is the key to preventing water inrush, and the identification and positioning of the water inrush channel is the basis for the grouting reinforcement design of the weathering groove of the submarine tunnel. Based on above research results, the F1 weathering trough was blocked and reinforced by the composite grouting method, and the engineering reinforcement effect was good.

This study aims to investigate the influence of soil–structure interaction (SSI) on the seismic response of a nuclear island (NI) building with base isolation. Hence, modal and dynamic time‐history analyses of the NI building with base isolation based on different soil dynamic numerical models that are applicable for homogeneous and layered sites to consider the SSI effect were conducted. After a comparison analysis of natural frequencies, floor response spectra (FRS), and acceleration response of superstructure, the following results are obtained. (i) For homogeneous sites, the degrees of freedom of the horizontal translation and torsion of the NI building with base isolation calculated using different site dynamic numerical models have equivalent natural frequencies. For layered sites, the natural frequencies increase slightly with the improvement of the shear wave velocity of the upper layered soil. (ii) For homogeneous sites, FRS calculated by the massless foundation model is generally larger than those of the dynamic model proposed by the ASCE code and the viscoelastic artificial boundary site model. Both the spectral and peak values of horizontal FRS at a low frequency band calculated by considering the SSI effect are larger than those without the SSI effect. (iii) For layered sites, both the spectral and peak values of horizontal FRS at a low frequency band have an amplification effect compared with that of a homogeneous site. (iv) For layered sites, the calculated horizontal acceleration response does not have evident law that changes with the degree of hardness and softness of the upper soil. Therefore, the SSI effect for particular homogeneous and layered sites should be considered when calculating the seismic response of the NI building with base isolation.

Purpose: In recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. This paper aims to propose a new 3D combined isolation bearing (3D-CIB) to mitigate the seismic response in both the horizontal and vertical directions.Design/methodology/approach: The new 3D-CIB composed of laminated rubber bearing coupled with combined disk spring bearing (CDSB) was proposed. Comprehensive analysis of constitution and theoretical derivation for 3D-CIB were presented. The advantage of CDSB is that the constitution can be flexibly adjusted according to the requirements of the bearing capacity and vertical stiffness. Hence, four different combinations of CDSB were designed for the 3D-CIB and employed to isolate nuclear reactor building. A comparative study of the seismic response in terms of seismic action, acceleration floor response spectra (FRS), peak acceleration and relative displacement response was carried out.Findings: 3D-CIB can effectively reduce seismic action, FRS and peak acceleration response of the superstructure in both the horizontal and vertical directions. Overall, the horizontal isolation effectiveness of 3D-CIB was slightly influenced by vertical stiffness. The decrease in the vertical stiffness of the 3D-CIB can reduce the vertical FRS and shift the peak values to a lower frequency. The vertical peak acceleration decreased with a decrease in the vertical stiffness. The superstructure exhibited a rocking effect during the earthquake, and the decrease in the vertical stiffness may increase the rocking of the superstructure.Originality/value: Although the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted by different constitutions, the vertical stiffness should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. This study of isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of nuclear power plants.

This paper aimed at evaluating the influence of different site conditions on the impact response of the structure of nuclear power plants (NPPs) against a large commercial aircraft. The lumped parameter site dynamic model recommended by the code of ASCE 4-98 was used to consider the different homogeneous sites. With respect to the excellent impact resistant performance of steel-plate concrete (SC) structure, the full SC containment is selected as the research object. The impact analysis of the full SC containment against a large commercial aircraft under different site conditions was carried out, based on the force time-history analysis method. The numerical results in terms of the displacement, plastic strain, local concrete damage, and different values of energy were evaluated. The results showed that: (1) For the relatively thin full SC containment, the impact response under the fixed boundary is the largest, while that calculated by other, different sites varies greatly, and there is no consistent rule, the boundary condition which is assumed to be fixed is relatively conservative. (2) For the thicker full SC containment, the displacement response decreased with the increasing of the site shear wave velocity, which is the smallest when the fixed boundary is considered. When the shear wave velocity of the site is large enough, its boundary condition which is assumed to be the fixed constraint is reasonable. (3) For the relatively thin full SC containment, the site damping effect has a significant effect on the structural impact response. Nevertheless, the impact response of the thicker containment is slightly influenced by the site damping effect. (4) For the impact analysis of the structures of NPPs against a large commercial aircraft, it is suggested that both the specific site condition and fixed boundary should be considered.

This paper aimed at evaluating the influence of different vertical equivalent damping ratios of a 3-dimensional combined isolation bearing (3D-CIB) as regards seismic response and isolation effectiveness. A comparative study of the seismic response in terms of acceleration floor response spectra (FRS), peak acceleration, displacement response of the nuclear reactor building, and dynamic response of the 3D-CIB was carried out. The results showed that: (1) the horizontal FRS is slightly influenced by the vertical equivalent damping ratio of 3D-CIB, whereas the increase of the vertical equivalent damping ratio has a significant effect on reducing the vertical FRS; (2) the peak vertical acceleration increased with the decrease in the vertical equivalent damping ratios of 3D-CIB and the difference of peak accelerations calculated by the damping ratio of 20 and 25% is within 10%; (3) the increase of the vertical equivalent damping ratio is capable of reducing the horizontal displacement and the rocking effect of the superstructure, and effectively controlling the vertical displacement amplitude; and (4) the vertical equivalent damping ratio of 3D-CIB has a slight effect on its axial force. Consequently, it is demonstrated that the increase of the vertical equivalent damping ratio is advantageous for isolation effectiveness. From the view of displacement control, it is suggested that the 3D-CIB with the vertical an equivalent damping ratio of 15~20% is appropriate and acceptable.

According to the requirements of nuclear safety regulations, nuclear power plants must be equipped with seismic instrumentation systems, which are mainly used for monitoring alarm and automatic shutdown alarm during an earthquake. Both the second and third generation NPPs adopt Peak Ground Acceleration (PGA). However, among the seismic acceleration characteristics, isolated and prominent single high frequency acceleration peaks have no decisive influence on the seismic response. Especially when the earthquake monitoring alarm is at 1 out of 7, it is likely to cause a false alarm or false shutdown. In addition, it usually takes one month or more for the NPPs to restart after the shutdown. In this paper, an improved seismic instrumentation system based on the existing system is proposed. For high intensity areas, three components resultant acceleration is used to judge the 2 out of 4 logic of the automatic seismic trip system(ASTS). For low intensity areas, the seismic failure level is evaluated quickly by using three components resultant acceleration, seismic instrument intensity, cumulative absolute velocity, floor response spectrum and other multi-parameters, avoiding unnecessary and long-term shutdown inspection.

Due to the excellent impact resistant performance of steel-plate concrete (SC) structure compared with the conventional reinforced concrete (RC) structure, SC structure is preferred to be used in the design of external walls of nuclear island buildings for new nuclear power plants (NPPs). This study aims at evaluating the effect of material and geometric parameters of SC containment on its impact resistant performance, thus the numerical simulation and sensitivity analysis of SC containment subjected to malicious large commercial aircraft attack are conducted based on the force time-history analysis method. The results show that: (1) the impact resistant performance of full SC containment is better than that of half SC containment; (2) for relatively thin full SC containment, the impact response and concrete damage can be significantly reduced by the enhancing of concrete strength grade or the increasing of steel plate thickness; (3) for the thicker full SC containment, concrete strength grade has only a slight influence on the impact displacement response, and the increasing of steel plate thickness has no significant effect on mitigating the impact displacement response. However, the increasing of steel plate thickness can effectively reduce its plastic strain, and the decreasing of strength grade of steel plate may obviously increase its plastic strain; and (4) concrete thickness plays a decisive role on the improvement of impact resistance, which is more effective than the enhancing of concrete strength grade. Resultantly, this paper provides a reference and guidance for the design of SC structure external walls of nuclear island buildings against a large commercial aircraft.