Figure 2 - uploaded by Ali Nour
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CANDU 6 reactor building and 3D finite element model.
Citations
... As seen in Fig. 5, four SDOF structures with different fundamental frequencies (i.e., 10 Hz, 5 Hz, 1 Hz, and 0.5 Hz) are considered. Since Linear Time-History Analysis (LTHA) is usually applied to estimate dynamic behavior of nuclear power plant structures under serviceability conditions [3,46,47], we apply LTHA to determine FRS of all structures in the study. ...
The floor response spectra (FRS) are usually determined by time history analyses using spectrum-matched time histories. However, previous studies reported that spectrum-matched time histories may cause a biased estimate of FRS, which raises a challenge of FRS generation for nuclear power plant structures. The study focuses on resolving the challenge. We begin the study by discussing characteristics of amplitude-scaled and spectrum-matched ground motions for seismic design and analysis of nuclear facilities. Then, we explore the influence of spectral matching on the change of ground motion parameters. Using suites of amplitude-scaled and spectrum-matched ground motions, we determine FRS for examples of typical structures, and investigate how the change of ground motion parameters due to spectral matching affects the biased estimate of FRS. The investigation shows that, the change of damping scaling factor is remarkably correlated with the biased estimate of FRS. Thus, we propose the improved spectrum-matched time histories for floor response spectra generation. Taken a service building of nuclear power plants as an example, the study shows that, the improved spectrum-matched are adequate to achieve approximate unbiased estimate of FRS under different damping values.
... Current seismic code provisions [1][2][3][4][5][6] state that one of the methods which can be used for the seismic analysis and design of R/C structures is the Linear Response History Analysis (LRHA). Moreover, manyengineers have already been using this method for analyses in advanced applications, such as bridges, dams, nuclear facilities etc. [7][8][9]. In this method a three-dimensional mathematical model is analysed using simultaneously imposed consistent pairs of earthquake ground motion records along each of the two horizontal structural axes (with a few exceptions, the vertical component of the ground motion is allowed to be ignored as its influence on seismic response is considered negligible). ...
The objective of the present work is to evaluate four procedures for selecting the sectional forces for design purposes in the nonlinear range of behavior in case of multistorey buildings. For this purpose amultistorey asymmetric building designed using thefour procedures is analyzed by Nonlinear Response History Analysis (NRHA) underseven bi-directional earthquake ground motions. The two horizontal accelerograms of each ground motion are applied along horizontal orthogonal axes forming an angle θ=0°, 30°, 60°, …, …, 330° with the structural axes. Moreover, two different seismic intensity levels are considered by using two appropriate multipliers for each ground motion. For the evaluation of inelastic structural behavior the maximum interstorey drift ratio of the building is computed. The analyses results show that the overall damage state of the building is significantly affected by the procedure used to select the design sectional forces. The building designed using the procedure based on the maximum normal stress over all seismic incident angles shows the best seismic performance.
... Nour et al. 2012 [17]). Therefore, the proposal of a validated code-based LTHA design framework for 74 buildings, which can be implemented in EC8, represents an important opportunity for engineers. ...
A novel framework for Eurocode 8-compliant design using Linear Time-History Analysis (LTHA) is discussed. LTHA overcomes the approximations typical of other linear seismic analyses but it still lacks a suitable approach for seismic input selection compatible with Eurocode 8-prescriptions. The critical aspect is to find a balanced compromise to control seismic input variability, suiting design purposes, but still being able to capture specific response features such as pulse-like effects. A LTHA design procedure has been included in ASCE/SEI 7-16 (2017) and described in FEMA P-1050 (2015), suggesting spectral-matching of three ground motions as input, so that LTHA can be used as alternative to Response Spectrum Analysis (RSA). Herein, a 12-storey regular Reinforced-Concrete Moment-Resisting-Frame building is employed as case-study. Different ground motion selection strategies are compared. Firstly, three suites of spectrum-compatible ground motions are used referring to requirements of Eurocode 8 for nonlinear time-history analysis and compared with LTHA-ground motion selection procedure included in FEMA P-1050.
A new index for LTHA ground motion selection (Ieq) is proposed to control response variability in relation to the dynamic properties of the structure aimed at obtaining a suitable input for LTHA design. A target value for Ieq is proposed on the basis of structural response for far-field and near-field suites and an ad hoc suite of pulse-like ground motions selected considering pulse periods lower than the fundamental period of the structure. The difference in terms of design results between LTHA and RSA is employed as benchmark to evaluate the suitability of Ieq for LTHA design.
... An elastic model of the containment structure was developed, and the dynamic properties of the model are compared with the dynamic properties of a similar CANDU 6 containment which were identified from an ambient vibration test. 7 As shown in Figure 2A,B, the whole containment structure including the base slab, perimeter wall, buttresses, ring beam, and the double dome system was modeled using 10-node tetrahedral elements. Stiffness reduction due to 3 permanent equipment openings in the perimeter wall was also taken into account. ...
... From the eigenvalue analysis, the first and second fundamental frequencies are found to be 5.20 and 7.87 Hz, respectively, which are slightly higher than 4.2 and 7.5 Hz, obtained from the ambient vibrations measurements of a similar CANDU 6 type containment structure. 7 The model participation factor for the first mode is 0.81. The effective modal masses of the first and second modes of the structure are 1.200 × 10 4 tons and 7.226 × 10 3 tons, respectively, and the total modal effective masses of the first 2 modes are around 85% of the total structural mass. ...
This study evaluates capabilities of the VecTor4 computer program to assess the seismic performance of a concrete containment structure subjected to both design-basis and beyond design-basis earthquakes. Based on a detailed nonlinear finite element model of the nuclear power plant containment structure, the seismic performance in terms of stress and strain distributions, cracks, yielding of reinforcement bars and tendons, as well as overall failure mechanism, is thoroughly reviewed. In addition, the post-seismic performance of the containment structure subjected to a subsequent pressure increase is also investigated. Consideration is also given to the time-dependent parameters of creep, shrinkage, and relaxation of prestressing tendons. It is found that the time-dependent parameters and earthquake have a non-negligible impact on pressure-induced structural performance but that this impact can be predicted for a given earthquake. The proposed method is useful for assessing the progressive failure behaviour of containment structure under chain events.
... Many studies, e.g. (Hanamura et al. 1996, Ghiocel 2009, Nour et al. 2012) focused on investigating the seismic responses of the non-isolated NPPs considering the ground motions spatial variation. Nonetheless, very few studies have been conducted to study and examine the seismic responses of BI-NPPs considering spatially varying ground motions. ...
This study presents the effects of the spatial variation of ground motions in a hard rock site on the seismic responses of a base-isolated nuclear power plant (BI-NPP). Three structural models were studied for the BI-NPP supported by different number of lead rubber bearing (LRB) base isolators with different base mat dimensions. The seismic responses of the BI-NPP were analyzed and investigated under the uniform and spatial varying excitation of El Centro ground motion. In addition, the rotational degrees of freedom (DOFs) of the base mat nodes were taken to consider the flexural behavior of the base mat on the seismic responses under both uniform and spatial varying excitation. Finally, the seismic response results for all the analysis cases of the BI-NPP were investigated in terms of the vibration periods and mode shapes, lateral displacements, and base shear forces. The analysis results indicate that: (1) considering the flexural behavior of the base mat has a negligible effect on the lateral displacements of base isolators regardless of the number of the isolators or the type of excitation used; (2) considering the spatial variation of ground motions has a substantial influence on the lateral displacements of base isolators and the NPP stick model; (3) the ground motion spatial variation effect is more prominent on lateral displacements than base shear forces, particularly with increasing numbers of base isolators and neglecting flexural behavior of the base mat.
