Abstract
Base isolation can be used to reduce seismic response of structure and protect the structure from damage subjected to earthquake. To study the isolation effect of new PWR nuclear power plant with a base isolation system, considering FSI (fluid-structure interaction) effect by the simplified model, two 3D numerical models (one nonisolated model and one isolated model) were established. After natural frequency analysis, one artificial ground motion was chosen to analyze isolation effect qualitatively. Based on the results, the accelerations and relative displacements of nuclear island building under ten natural ground motions were statistically analyzed to evaluate the isolation effect quantitatively. The results show that the base isolation system can reduce the natural frequencies of nuclear island building. Horizontal accelerations can be reduced effectively, but the isolation effect is not obvious in vertical direction. The acceleration reduction ratio of the top is about 70%–90%, and the acceleration reduction ratio of the lower part is about 20%–60%. Horizontal displacement of the isolated model is far larger than that of the nonisolated model, and horizontal displacement will become larger considering FSI effect. These conclusions could provide some references for studies on the isolation system of nuclear island building.
Highlights
It has been proved that the simplified method has a good result in simulating the seismic response of the whole nuclear island building considering FSI effect
This simplified method is used for analysis. e schematic diagram of the simplified model is shown in Figure 4, and the details of the simplified model have been reported in reference [11]
Using ABAQUS, modal analysis of two models is studied. e first two natural frequencies are listed in Table 3. e 1st mode is the translation of structure in Y-direction, and 2nd mode is the translation of structure in X-direction. e first two frequencies of model two are 0.727 Hz and 0.769 Hz separately, and the relative error of fundamental frequency between theoretical formula and numerical analysis is 1.5%. It illustrates that the theoretical assumption of a single degree-of-freedom system and the numerical method of modal analysis are both reasonable. e first two natural frequencies are far larger than the 1st sloshing frequency of cooling water (0.13 Hz), and the resonance of cooling water in the water tank will not occur in dynamic analysis
Summary
For the concept design of isolation bearings, the relevant experts and scholars have done some research and given the suggestions [21, 22]. In addition to bearing the load of nuclear island building, the resonance of cooling water in the water tank should be avoided. In the author’s previous research [11], 1st sloshing frequency of cooling water is about 0.13 Hz. So, the isolation bearings are chosen to ensure that 1st frequency of isolation structure is greater than 0.4 Hz. Considering the foundation size, total mass, dynamic characteristics of nuclear island building, and so on, leadrubber bearing GZY1000 is selected as the isolation bearing for the dynamic analysis of the nuclear island building after a series of trial calculations [23]. To ensure that the nuclear island building will not be damaged due to excessive torsion, the center of mass and the center of stiffness of the isolated structure need to coincide approximately. E total mass of nuclear island building is about 2.2 × 105 t, and the average vertical load of one isolation bearing is 6094 kN.
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