Investigating the Effect of Depth and Impedance of Foundation Rock in Seismic Analysis of Gravity Dams

2014 ◽  
Vol 5 (2) ◽  
pp. 1-18
Author(s):  
Sharad Joshi ◽  
Ishwer Datt Gupta ◽  
Lalitha R. Pattanur ◽  
Pranesh B. Murnal
Keyword(s):  
Half Space ◽  
Seismic Analysis ◽  
Free Field ◽  
Time History ◽  
Gravity Dams ◽  
Ground Acceleration ◽  
Rock Interaction ◽  
Foundation Block ◽  
Substructure Approach ◽  
Foundation Rock

The inhomogenieties of the foundation can be modeled explicitly in standard FEM procedure, however, the results vary significantly with the extent of foundation block modeled and mechanism of applying the input earthquake excitation. The substructure approach provides mathematically exact solution but assumes average properties for the entire foundation as viscoelastic half space. This paper has carried out detailed investigations with varying impedance contrasts and different size of foundation block to show that the results, with suitably deconvoluted free-field ground acceleration time-history applied at the base of foundation block in the FEM approach, are in good agreement with the substructure approach. However, the other variants of the FEM approach may lead to erroneous and overestimated stresses in the dam body. As the foundation of gravity dams can generally be approximated as an equivalent homogeneous half-space, the more accurate and efficient substructure approach can be used to model the dam-foundation rock interaction (SSI) effects in most practical situations.

Seismic Analysis Approach Applied to a Small Size Next Generation Nuclear Reactor

2008 ◽  
Author(s):  
G. Forasassi ◽  
R. Lo Frano
Keyword(s):  
Nuclear Power ◽  
Nuclear Reactor ◽  
Seismic Analysis ◽  
Methodological Approach ◽  
Free Field ◽  
Time History ◽  
Future Generation ◽  
Energy System ◽  
Ground Acceleration ◽  
Input Motion

The aim of the paper is to evaluate the behaviour of a Near Term nuclear energy system example with reference to IRIS (International Reactor Innovative and Safety) project. As it is well known the development of new and future-generation nuclear power plant (Gen IV NPP) is strictly related to the sustainability, safety and reliability as well as to the proliferation resistance. In this paper, the safety aspects related to the effects of a severe earthquake (Safe Shutdown Earthquake) as well as to the induced loads are treated by means the Substructure and Time History Approaches, assuming a free field Peak Ground Acceleration equal to 0.3 g as input motion. The analyses and upgrading of the geometry structures with highest probability of criticality are performed on rather complex and detailed 3D finite element (FE) models. The main goals were: the evaluation of the dynamic characteristics of each considered structure, the verification of the load bearing structures in order to obtain a preliminary assessment of the adopted methodological approach and structural models. The analyses results and dynamic response of internal components (e.g. Nuclear Buildings, etc.) seem to confirm the possibility to upgrade the geometry and the performances of the proposed design choices.

Study on Methods for HCLPF Value of Nonlinear Supports System of Steam Generator

2018 ◽  
Author(s):  
Feng-chun Cai ◽  
Xian-hui Ye ◽  
Qian Huang ◽  
Wenzheng Zhang
Keyword(s):  
Steam Generator ◽  
Nonlinear Model ◽  
Seismic Analysis ◽  
Time History ◽  
Nonlinear Time History Analysis ◽  
Cost Calculation ◽  
Seismic Capacity ◽  
Ground Acceleration ◽  
Reactor Building ◽  
Nonlinear Time History

High confidence of low probability of failure (HCLPF) values of equipment, representing the seismic capacities of the equipment, are the fundamental ingredient in seismic probability safety assessment (SPSA) and seismic margin analyses (SMA). In this paper, two methods for calculating the HCLPF values of equipment were investigated, fragility analysis, and conservative deterministic failure margin (CDFM). These methods are linear methods. Based on these methods, HCLPF value of equipment can be computed conveniently by scaling the results of the existing seismic analysis. For a nonlinear systems, the HCLPF values based on these linear scaling methods are unrealistic. For a complicated nonlinear equipment or structure, a detail nonlinear model was used to derive the seismic capacity. The results by this method are realistic, but cost calculation time. In this paper, a nonlinear model of reactor coolant system coupled reactor building was built. This model includes the steam generator and considers the nonlinear factors of steam generator such as gap in the supports, plasticity of hot leg and cold leg. Forced motion was applied to the base of reactor building. And seismic response of the steam generator was calculated iteratively by scaling the ground motion level step by step. Based on these calculations, a curve of load on the supports VS peak ground acceleration (PGA) can be obtained. Then based on these curves and allowable load of supports of steam generator, which derived from stress analysis on support of steam generator, seismic capacity of the supports of steam generator was determined. Then the HCLPF Value of the supports of steam generator was obtained by this nonlinear time history analysis and was compared with the results based on the CDFM. The two results were different. Therefore, the HCLPF seismic capacity of equipment with nonlinearity, such as gap nonlinearity, should be calculated by nonlinear time history method.

scholarly journals Performance-based seismic assessment of vulnerability of dam using time history analysis

2018 ◽  
Vol 149 ◽  
pp. 02035
Author(s):  
Oumnia Elmrabet ◽  
Hasnae Boubel ◽  
El Mehdi Echebba ◽  
Mohamed Rougui ◽  
Ouadia Mouhat
Keyword(s):  
Soil Structure ◽  
Seismic Vulnerability ◽  
Seismic Analysis ◽  
Time History ◽  
Time History Analysis ◽  
Seismic Assessment ◽  
Assessment Procedure ◽  
Ground Acceleration ◽  
History Analysis ◽  
Al Hoceima

The current performance-based seismic assessment procedure can be computationally intensive as it requires many time history analyses (THA) each requiring time intensive post-processing of results. Time history analysis is a part of structural analysis and is the calculation of the response of a structure to any earthquake. It is one of the main processes of structural design in regions where earthquakes are prevalent. The objective of this study is to evaluate the seismic performance of embankment dam located on the Oued RHISS in the Province of AL HOCEIMA using the THA method. To monitor structural behavior, the seismic vulnerability of structure is evaluated under real earthquake records with considering the soil-structure-fluide interaction. In this study, a simple assistant program is developed for implementing earthquake analyses of structure with ANSYS, ground acceleration–time history data are used for seismic analysis and dynamic numerical simulations were conducted to study and identify the total response of the soil-structure system.

Seismic Analysis for the Subsea Pipeline System

2010 ◽  
Author(s):  
Rosman B. Arifin ◽  
Wan M. Shafrizal B. Wan M. Yusof ◽  
Pengfei Zhao ◽  
Yong Bai
Keyword(s):  
Seismic Wave ◽  
Seismic Analysis ◽  
Ground Deformation ◽  
Time History ◽  
Metal Loss ◽  
Pipeline System ◽  
Wave Impact ◽  
Ground Acceleration ◽  
Permanent Ground Deformation ◽  
The Impact

Seismic activity in Malaysia is very low as earthquakes are infrequent in this region. The strongest measured earthquake magnitude record in this region since 1978 was 4, which had a very low impact on the integrity of pipelines system in Malaysia. Although this is the case, there exists seismic events in the neighbouring regions and such events may impact the operability, stability and safety of Malaysia submarine pipeline systems. Based on this, a pipeline integrity analysis has been carried out to check the pipeline integrity under the seismic influence. The purpose of the analysis includes: • To calculate earthquake response for three PCSB PMO main export pipelines — for each pipeline both buried and unburied conditions will be taken into account. • To understand the characteristics of buried and unburied pipelines under strong earthquakes affecting Malaysia waters. • To determine the peak ground acceleration (PGA) the pipelines can withstand. • To determine the largest permanent ground deformation (PGD) the pipeline can withstand. • To estimate the impact of the metal loss on the pipeline integrity. • To assist PETRONAS to prepare for such severe earthquakes. Two typical methods have been employed to make the analysis: • Time history method is used to calculate both buried and unburied pipeline response. Two typical seismic wave records have been used in the analysis, which will give a better estimation of the pipeline response under the seismic wave impact. • Soil-pipe element method is used to simulate the behavior between the soil and buried pipeline system. Based on choosing the suitable experimental equations, this method can simulate the soil behaviour accurately. This paper discusses results of the seismic analysis. Based on the analysis results, the pipeline system will be safe under the seismic wave impact. More attention should be given to fault hazard, as the pipeline system will been failed under the fault impact. Finally, the metal loss will be taken into consideration, for the pipeline stress will be much higher due to great metal loss. All those analysis results will be further utilised to estimate the pipeline response in the case of the earthquake.

Lateral Structure Interaction With Seismic Waves

1971 ◽  
Vol 38 (1) ◽  
pp. 125-134 ◽  
Author(s):  
R. J. Scavuzzo ◽  
J. L. Bailey ◽  
D. D. Raftopoulos
Keyword(s):  
Half Space ◽  
San Francisco ◽  
Nuclear Power ◽  
Power Plants ◽  
Seismic Waves ◽  
Structural Characteristics ◽  
Free Field ◽  
Elastic Half Space ◽  
Inertia Force ◽  
Ground Acceleration

The interaction of lateral structural inertia forces with horizontal seismic motion is formulated in terms of an integral equation of the Volterra type. By means of normal mode theory the inertia force at the base of the structure is expressed as a function of the foundation motion. After the motion of the two-dimensional elastic half space resulting from a uniform horizontal foundation force varying arbitrarily with time over a specified interval on the boundary of the half space has been determined, the interaction equation is derived. Numerical studies for two free-field acceleration inputs are made for different ground stiffnesses and structural characteristics. The first of these free-field inputs is a ramp sine function and the second is the east-west ground acceleration recorded at Golden Gate Park during the 1957 San Francisco earthquake. The interaction effects for structures similar to nuclear power plants prove to be significant.

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