• Earthquakes and Structures
• /
• v.14 no.1
• /
• pp.33-44
• /
• 2018

Base-isolated nuclear power plant (BI-NPP) structures are founded on expanded basemat as a flexible floating nuclear island, are still lacking the recommendation of the consideration of incoherent motion effect. The effect of incoherent earthquake motion on the seismic response of BI-NPP structure has been investigated herein. The incoherency of the ground motions is applied by using an isotropic frequency-dependent spatial correlation function to perform the conditional simulation of the reference design spectrum compatible ground motion in time domain. Time history analysis of two structural models with 486 and 5 equivalent lead plug rubber bearing (LRB) base-isolators have been done under uniform excitation and multiple point excitation. two different cases have been considered: 1) Incoherent motion generated for soft soil and 2) Incoherent motion generated for hard rock soil. The results show that the incoherent motions reduce acceleration and the lateral displacement responses and the reduction is noticeable at soft soil site and higher frequencies.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.26 no.6
• /
• pp.237-246
• /
• 2022

Based on the random-vibration-theory methodology, dynamic responses of nuclear facilities subjected to obliquely incidental and incoherent earthquake ground motions are calculated. The spectral power density functions of the 6-degree-of-freedom motions of a rigid foundation due to the incoherent ground motions are obtained with the local wave scattering and wave passage effects taken into consideration. The spectral power density function for the pseudo-acceleration of equipment installed on a structural floor is derived. The spectral acceleration of the equipment or the in-structure response spectrum is then estimated using the peak factors of random vibration. The approach is applied to nuclear power plant structures installed on half-spaces, and the reduction of high-frequency earthquake responses due to obliquely incident incoherent earthquake ground motions is examined. The influences of local wave scattering and wave passage effects are investigated for three half-spaces with different shear-wave velocities. When the shear-wave velocity is sufficiently large like hard rock, the local wave scattering significantly affects the reduction of the earthquake responses. In the cases of rock or soft rock, the earthquake responses of structures are further affected by the incident angles of seismic waves or the wave passage effects.

• Earthquakes and Structures
• /
• v.26 no.5
• /
• pp.401-416
• /
• 2024

Long-span structures, such as bridges, can experience different seismic excitations at the supports due to spatially variability of ground motion. Regarding current bridge designing codes, it is just EC 2008 that suggested some regulations to consider it and in the other codes almost ignored while based on some previous studies it is found that the effect of mentioned issue could not be neglected. The current study aimed to perform a comprehensive study about the effect of spatially varying ground motions on the dynamic response of a reinforced concrete bridge under asynchronous input motions considering soil-structure interactions. The correlated ground motions were generated by an introduced method that contains all spatially varying components, and imposed on the supports of the finite element model under different load scenarios. Then the obtained results from uniform and non-uniform excitations were compared to each other. In addition, the effect of soil-structure interactions involved and the corresponding results compared to the previous results. Also, to better understand the seismic response of the bridge, the responses caused by pseudo-static components decompose from the total response. Finally, an incremental dynamic analysis was performed to survey the non-linear behavior of the bridge under assumed load scenarios. The outcomes revealed that the local site condition plays an important role and strongly amplifies the responses. Furthermore, it was found that a combination of wave-passage and strong incoherency severely affected the responses of the structure. Moreover, it has been found that the pseudo-static component's contribution increase with increasing incoherent parameters. In addition, regarding the soil condition was considered for the studied bridge, it was found that a combination of spatially varying ground motions and soil-structure interactions effects could make a very destructive scenarios like, pounding and unseating.