Simplified Seismic Analysis Methods Research Articles

Influence of soil to structure stiffness on the accuracy of the pushover method for underground structures

The pushover method for underground structures is a seismic analysis method featured by high calculation accuracy and a simple implementation process. The method has been widely used in seismic design and other related scientific research; however, the influence of different soil-structure flexibility ratios on the accuracy of this method is still not well understood. In this study, we select the cross-section structures beneath the Daikai subway station as the research object and establish 12 finite element analysis models with different soil-structure flexibility ratios using ABAQUS. All models are computed by the dynamic time-history method or the pushover method. Furthermore, the dynamic time-history solution result is taken as the standard solution, and the precision and application of the pushover analysis method are discussed based on the parameters of peak interlayer displacement and peak internal force of the middle column section. The results show that the soil-structure flexibility ratio has a significant influence on the calculation accuracy of the pushover method, and the calculation accuracy of this method is the most ideal when the soil-structure flexibility is equal to 1. The research results can provide significant references for the seismic design of underground structures or the improvement of simplified seismic analysis methods.

Allowable Torsional Eccentricity for the Simplified Method for the Seismic Analysis of Low-Rise Confined Masonry Shear-Wall Buildings of Mexican Codes

A parametric study devoted to assess the limiting value for the static eccentricity (es) for the application of the simplified method for seismic analysis (SMSA) of bearing-wall confined masonry structures of Mexican Building Codes is presented. Based upon the results of a comprehensive parametric study, limiting values for es for the use of the SMSA are proposed for three different performance levels for the structure: (a) elastic response, (b) completely nonlinear (cracked) response of all walls along the building height and, (c) partially nonlinear (cracked) response along the height. The criterion used to propose limiting values for es was that the underestimation of shear forces predicted for the first story walls with the SMSA was within reasonable limits with respect to those shear forces computed with a rigorous 3D static analysis using an equivalent linearization for the nonlinear (cracked) response of the walls, in order to insure reasonably safe designs of such structures.

A Simplified Method for Seismic Analysis of Tanks with Floating Roof by using Finite Element Method: Case Study of Kharg (Southern Iran) Island Tanks

Tanks with floating roof have shown high vulnerability subjected to past earthquakes, such as Kobe, and Izmit. The main cause of damage is believed to be the interaction between the floating roof and the tank wall. In this paper a simplified method is presented for modeling the floating roof and its interaction with the tank wall, making it possible to use Finite Element Analysis (FEA) for calculating the seismic response of tank-floating roof system. In the proposed method, assuming that the sloshing phenomenon is mainly suppressed by the floating roof, the seal between the roof and the tank's wall is modeled by introducing some radial pre-compressed ‘only-compression elements’ all around the roof, itself substituted by a rigid disk, and the tank's wall is modeled by 3-dimensional shell elements. The dynamic effect of the impounded oil in the tank is taken into account by the use of added mass concept. If during the time history analysis the maximum relative displacement between the roof disk and the tank's wall in any radial direction exceeds the initial length of the pre-compressed only-compression springs the tank is considered to be vulnerable. The proposed method has been applied to a tank sample in Kharg (southern Iran) island.

A simplified method for seismic analysis of rooftop telecommunication towers

A simplified method is presented in this paper for the estimation of forces at the base of telecommunication towers mounted on building rooftops due to seismic excitation. Although some codes and standards propose simplified methods for the evaluation of base shear forces for towers founded on ground, no method yet exists for the evaluation of overturning moments. The proposed simplified method is based on numerical simulations using truncated modal superposition, which is widely used for seismic analysis of linear structures. The method requires the prediction of input seismic acceleration at the building–tower interface, the definition of an acceleration profile along the building-mounted tower, and the determination or evaluation of the mass distribution of the tower along its height. The method was developed on the basis of detailed dynamic analyses of three existing towers assumed to be mounted separately on three buildings. It was found that the method yields conservative results, especially for the overturning moments.Key words: self-supporting towers, earthquake, horizontal excitation, dynamic analysis, acceleration, modal superposition.

Simplified Method for Seismic Analysis of Industrial Chimneys

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A simplified method for seismic analysis of lattice telecommunication towers

A simplified static method for estimating the member forces in self-supporting lattice telecommunication towers due to both horizontal and vertical earthquake excitations is presented in this paper. The method is based on the modal superposition technique and the response spectrum approach, which are widely used for seismic analysis of linear structures. It is assumed that the lowest three flexural modes of vibration are sufficient to correctly estimate the tower's response to horizontal excitation, while only the lowest axial mode is sufficient to capture the response to vertical excitation. An acceleration profile along the height of the tower is defined using estimates of the lowest three flexural modes or the lowest axial mode, as appropriate, together with the spectral acceleration values corresponding to the associated natural periods. After the mass of the tower is calculated and lumped at the leg joints, a set of equivalent static lateral or vertical loads can be determined by simply multiplying the mass profile by the acceleration profile. The tower is then analyzed statically under the effect of these loads to evaluate the member forces. This procedure was developed on the basis of detailed dynamic analysis of ten existing three-legged self-supporting telecommunication towers with height range of 30-120 m. The maximum differences in member forces obtained with the proposed method and the detailed seismic analysis are of the order of ±25% in the extreme cases, with an average difference of ±7%. The results obtained for two towers with heights of 66 and 83 m are presented in this paper to demonstrate the accuracy and practicality of the proposed method.Key words: self-supporting tower, earthquake, vertical excitation, dynamic analysis.

A simplified method for seismic analysis of lattice telecommunication towers

A simplified static method for estimating the member forces in self-supporting lattice telecommunication towers due to both horizontal and vertical earthquake excitations is presented in this paper. The method is based on the modal superposition technique and the response spectrum approach, which are widely used for seismic analysis of linear structures. It is assumed that the lowest three flexural modes of vibration are sufficient to correctly estimate the tower's response to horizontal excitation, while only the lowest axial mode is sufficient to capture the response to vertical excitation. An acceleration profile along the height of the tower is defined using estimates of the lowest three flexural modes or the lowest axial mode, as appropriate, together with the spectral acceleration values corresponding to the associated natural periods. After the mass of the tower is calculated and lumped at the leg joints, a set of equivalent static lateral or vertical loads can be determined by simply multiplying the mass profile by the acceleration profile. The tower is then analyzed statically under the effect of these loads to evaluate the member forces. This procedure was developed on the basis of detailed dynamic analysis of ten existing three-legged self-supporting telecommunication towers with height range of 30-120 m. The maximum differences in member forces obtained with the proposed method and the detailed seismic analysis are of the order of ±25% in the extreme cases, with an average difference of ±7%. The results obtained for two towers with heights of 66 and 83 m are presented in this paper to demonstrate the accuracy and practicality of the proposed method.Key words: self-supporting tower, earthquake, vertical excitation, dynamic analysis.

Simplified seismic analysis methods used by AECL for the seismic qualification of CANDU nuclear power plants

This paper presents some of the simplified procedures and methods used by AECL for the seismic qualification of CANDU Nuclear Power Plants (NPPs). The approaches described herein are well tested and have been used in Canada and elsewhere for a number of years. Most of these simplified seismic analysis, testing and inspection procedures, and their underlying principals, have been accepted by the Atomic Energy Control Board of Canada for licensing purposes. In this respect, a comprehensive inspection of completed NPPs, to determine their ability to safely survive a design basis earthquake (DBE), is a prerequisite for licensing of CANDU NPP's in Canada. Many of the methods and recommendations given in the following tie in closely with [1].

Simplified seismic analysis methods in the Federal Republic of Germany (FRG) — Application to low seismicity sites

Despite worldwide existing information and knowledge about earthquake consequences on structures and technical equipment, the design procedures used for nuclear power plants are based on theoretical and not on realistic assumptions. Except innecessary hardware measures, time-consuming calculations and operational disadvantages due to the results, for instance, of the piping design, are possible. Therefore, for almost a decade in the FRG efforts were undertaken to realize a more realistically oriented design procedure and to modify the corresponding licensing requirements, such as KTA rules. Due to objections of the licensing and regulation committee, a general change in the KTA rules, to be utilized for the design of our CONVOY plants, could not be achieved. Therefore a compromise had to be found, particularly for the design of piping systems. This compromise includes a pipe routing guidline (VR) and guidlines for planning and acceptance (PAR). However, the situation will remain unsatisfactory until the necessary modifications of the KTA rule, and their adoption to reality, have been realized.

Simplified seismic analysis methods in Japan

A great deal of effort has been paid to simplify the procedures to ensure seismic safety, which is one of the most complicated problems for nuclear power facilities in Japan. Two main achievements are introduced here as recent issues in the relevant fields. Through extensive analysis of the strong accelerograms obtained from various rock sites, a simplified method to obtain input earthquake ground motions on the harder rock site is introduced in the first part. The second is the introduction of a practical method to evaluate the effect of soil—structure interaction by means of the explicit solution of elastic wave propagation.

Simplified seismic analysis methods in Belgium

Seismic design and analysis of nuclear plant systems, structures and components have requested huge effort and tremendous costs in the past two decades. The extended use of sophisticated, linear response type methods (modal analysis, spectral response) and the associated conservatism are responsible for the significant stiffening of the piping systems and the multiplication of supports and snubbers. The remedy used against the seismic risk seems worse than the pain itself, and safety might be impaired rather than improved. Indeed, system stiffening increases the average load level in normal operation (stresses, fatigue, nozzle loads, etc.); supports do not behave ideally as assumed (friction, rust, etc.) and snubbers are remarkably unreliable. On the other hand, experience with actual earthquakes shows that industrial facilities designed using very simplistic seismic techniques, or even no seismic requirement at all, suffer essentially no damage, even in the case of a large earthquake. This paradox challenges the traditional seismic design techniques, and appeals for revised seismic qualification methods of piping systems. When the assumption of the occurrence of an earthquake event is made in a plant in operation, which has not been designed against seismic criteria, the use of the standard seismic qualification techniques is still more questionable; simplified (quasi-static) techniques offer in this case a valuable and economically justified alternative. The paper describes the application of the quasi-static “modified load coefficient method” to the seismic assessment of the piping in a nuclear plant in operation, designed during the pre-seismic era.

Simplified seismic analysis methods in France

This paper presents current French practice for seismic analysis of nuclear power plants; special emphasis is made on topics where simplified methods are currently applied. Attention is drawn to the consequences of design standardization of French NPPs on seismic analysis. standardization of French NPPs on seismic analysis. • • Determination of ground motion. • • Structure analysis (soil—structure interaction, superstructures, basemat uplift). • • Equipment analysis (floor response spectra, primary loop, piping systems, bridge cranes).