The silo lateral pressure is an important parameter in the seismic design of squat silo. However, there is no exact theoretical calculation formula in the current silo code and the existing literature. The current study aimed to directly derive a new formula for calculating the seismic lateral pressure of squat silos in a simplified way. Firstly, based on Coulomb theory, regarded the silo as a special curved retaining wall and took the sliding wedge unit as the study object. Secondly, used the pseudo-static method and the rotating seismic angle method to simplify seismic forces and perform limit equilibrium analysis to derive the calculation formula. Finally, we verified the proposed formula by numerical simulation and parametric analysis. The results showed that silo wall friction could not be ignored, while the material cohesion is small enough to be ignored during engineering. For a large-diameter squat silo in a flat stack condition, a change in the radius has less influence on the side pressure strength, and the squat silo can be simplified as a linear retaining wall, while the lateral pressure strength increases as the radius increases in the conical stack condition. In addition, the measurement data and simulation calculation were close to the formula calculation, indicating the superiority of the new formula. These research results could provide a reference basis for improving the calculation of the seismic lateral pressure of silo specifications.
This paper improves the vibration isolation effect of the conventional wave impeding block by double-layer wave impeding block with the same thickness. Based on the theory of wave motion in unsaturated porous medium and elastic medium, the vibration isolation performance of double-layer wave impeding block in unsaturated foundation under SV wave incidence is studied. Based on the Helmholtz principle, the solutions of surface vertical displacements of the unsaturated foundation under SV wave incidence are obtained. The influence of the wave impedance ratio between the layers of double-layer wave impeding block and the wave impedance ratio at the interface between the wave impeding block and the unsaturated soil foundation are firstly studied, and it was found that the optimal vibration isolation effect could be obtained by designing and controlling the wave impedance ratio between the layers of the double-layer wave impeding block and the wave impedance ratio at the interface between the wave impeding block and the unsaturated foundation. Then the physical and mechanical parameters such as incidence angle, incidence frequency, saturation, thickness and burial depth of the double-layer wave impeding block were analyzed to determine the influence on the vibration isolation performance of the double-layer wave impeding block. The results show that the best vibration isolation effect of double-layer wave impeding block is achieved at 5° of S-wave incidence angle. The double-layer wave impeding block has better vibration isolation effect at low frequency, medium frequency and high frequency. The vibration isolation effect of double-layer wave impeding block increases and then decreases with an increase of saturation, increases with an increase of burial depth and thickness, decreases and then increases with an increase of incident frequency.
This paper proposes a new method for seismic fragility analysis of nuclear power plants (NPPs) considering the uncertainty sources of both ground motions and structural parameters. Based on the conventional seismic fragility model that only contains the uncertainty of ground motions, seismic fragility analysis conditioned on a specific seismic intensity is probabilistically reformulated by further incorporating the uncertainty of structural parameters. To improve the efficiency of the analysis, a point estimation-assisted incremental dynamic analysis was developed for evaluating the seismic fragility model including the uncertainty of structural parameter. The accuracy and efficiency of the proposed method were demonstrated by a single-degree-of-freedom system, where Monte Carlo simulation method is used for comparison. The seismic fragility based on the finite element model of an AP1000 NPP was analyzed using the proposed method. The results reveal that the safety of NPP structure would be overestimated without considering the uncertainty of structural parameter and the influence of the uncertainty of structural parameters on the seismic fragility of NPP presents an upward trend as the damage level increases. Furthermore, the sensitivity analysis of different structural parameters reveals that elastic module may have a dominant influence.
中强地震发生后,地震检测因受到尾波的干扰可能会遗漏部分微震事件,影响地震目录的完备性.文章利用波形模板匹配方法对2020年新疆伽师Ms6.4地震序列开展微震检测,相比原始的中国地震台网中心统一地震目录,新检测出1 756个微震事件,地震数量增加了 1.3倍.基于检测后的余震目录计算最小完备震级为ML1.2,地震活动性b值为0.76,较原始目录的ML1.6和0.77均有所降低.通过伽师震源区地震序列活动特征分析,结果表明前震序列在主震前短时间内(前36小时)出现地震活动的密集增强,相应的b值显示为低值;主震发生后地震序列完备震级较高,随着时间的推移,完备震级缓慢降低并趋于稳定,并且呈周期性的波动.本研究提高了伽师震源区地震目录的完备性,为精细化描述该地区地震序列时空演化特征提供了关键数据基础.
为研究麦积山石窟人行栈道在地震作用下的动力响应,选取154石窟处栈道作为典型结构,利用ABAQUS建立三维实体模型,充分考虑麦积山石窟地震环境条件,基于麦积山石窟窟区地震危险性评价结果,分析石窟栈道在50年超越概率63.5％、10％、2％水准所对应地震作用下的加速度响应、应力和损伤分布情况,进而对栈道结构抗震性能水准进行划分.结果表明,在地震作用下,栈道结构斜梯加速度响应明显大于平台板处加速度响应,平台板随其所处位置高度的增加,加速度响应峰值增大;栈道结构悬臂梁与岩体嵌固的端部混凝土应力数值较大,斜梯梁与悬臂梁相交处钢筋应力较大;随地震作用的增大,栈道结构混凝土拉压损伤出现范围和数值均呈增大趋势,且主要集中在悬臂梁与岩体嵌固端部,呈现出上部受拉、下部受压的典型破坏特征;基于栈道结构材料应力应变和构件损伤程度对其抗震性能水准进行划分,栈道在多遇(PGA=70 gal)、设防(PGA=240 gal)地震作用下,地震损伤评估结果均为轻度损坏,在罕遇(PGA=450 gal)地震作用下,地震损伤评估结果为严重损坏.该研究结果可为麦积山石窟栈道震损评估和加固设计提供科学依据.
