Seismic Design Spectra Research Articles

New seismic design spectra for nuclear power plants

New seismic design spectra for nuclear power plants

New seismic design spectra for nuclear power plants

Under a US Nuclear Regulatory Commission-sponsored project recommendations for seismic design ground motions for nuclear facilities are being developed. These recommendations will take several forms. Spectral shapes will be developed empirically and augmented as necessary by analytical models. Alternative methods of scaling the recommended shapes will be included that use a procedure that integrates over fragility curves to obtain approximately consistent risk at all sites. Site-specific soil effects will be taken into account by recommending site-specific analyses that can be used to modify rock hazard curves at a site. Also, a database of strong motion records will be archived for the project, along with recommendations on the development of artificial motions. This will aid the generation of motions for detailed soil- and structural-response studies.

A PROCEDURE FOR ESTIMATING INPUT ENERGY SPECTRA FOR SEISMIC DESIGN

In this paper, the damage potential of an earthquake ground motion is evaluated in terms of the total power of the acceleration of the ground motion. By assuming an appropriate spectral shape for the input energy spectrum, and using the well-known Parseval theorem for evaluating the total power of a random signal, the peak amplification factor for the equivalent input energy velocity spectrum can be determined. It is shown that the peak amplification factor for the input energy spectrum depends on the peak-ground-acceleration to peak-ground-velocity ratio and duration of the strong motion phase of the ground motion. Values for the equivalent input energy velocity amplification factor vary from about 2 to 10 for most of the recorded ground motions used in this study. Although a considerable scatter of data is observed in this study, the peak amplification factor predicted by the Fourier amplitude spectrum of the ground acceleration provides a fairly good estimate of the mean value of the peak input energy compared to that determined from inelastic dynamic time history analyses, particularly for systems with high damping and low lateral strength. The peak amplification factor derived in this paper provides a more consistent approach for estimation of seismic demand when compared to an earlier empirical expression used for the formulation of duration-dependent inelastic seismic design spectra, even though only a slight difference in the required lateral strength results from the use of the new formula.

Formulation of Duration-Dependent Inelastic Seismic Design Spectrum

In this paper, a procedure for developing the duration-dependent inelastic seismic design spectrum is proposed. The approach assumes that the lateral strength of the structure can be increased to compensate for the increased number of inelastic cycles that may be imposed on the structure under a long duration ground motion. Seismic input energy is considered as a part of the demand on the structure, and an empirical prediction of the seismic input energy in terms of the ground motion duration is made. Seismic design is established by requiring the structure to have a cyclic plastic strain energy capacity that is larger or equal to the portion of the seismic input energy contributing to cumulative damage. The plastic strain energy capacity of the structure is calculated using an energy-based cumulative damage model. Results from this study indicated that an increase in the lateral strength demand can be expected for an increase in the duration of the ground motion, and the increase in lateral strength is largest near the characteristic period of the ground motion. The strength deterioration parameter that characterizes the plastic strain energy capacity of the structure has been found to have a significant influence on the duration-dependent inelastic seismic design spectrum.

Seismic hazard assessment and design spectra for the Kozani-Grevena region (Greece) after the earthquake of May 13, 1995

The Kozani-Grevena (Greece) destructive earthquake occurred in a region of low seismicity. A considerable amount of strong-motion data was acquired from the permanent strong motion network of the Institute of Engineering Scismology and Earthquake Engineering (ITSAK) as well as from a temporary one installed after the earthquake. On the basis of this data set as well as on the observed macroseismic intensities, local attenuation relations for peak ground acceleration and velocity are proposed. A posteriori seismic hazard analysis is attempted for the affected and surrounding areas in terms of peak ground acceleration, velocity, bracketed duration and spectral acceleration. The analysis shows that the event of May 13, 1995 can be characterized as one with a mean return period of 500 to 1000 years. Relying on the observed spectral-acceleration amplification factors and the expected peak ground acceleration for mean return period of 500 years, region-specific elastic design spectra for the buildings of the Kozani and Grevena prefectures are proposed.

建築構造物を対象とした設計用入力地震動の強さ

The recent philosophies and methods in seismic design of buildings are discussed. In these two or three decades, several kinds of new type buildings have been constructed in Japan, that is, high rise buildings, nuclear power plant structures, base isolated buildings, structures on soft soil ground in so called “Water front” areas, and so on. These social demands of constructions have needed new philosophy and method for seismic design. On the other hand, the recent earthquake events occurred in the world, for instance, the 1968 Tokachi-oki earthquake, the 1979 Imperial Valley earthquake, the 1985 Michoacan earthquake and others, showed us important information. The actual situations of building damage and the observed data by strong motion seismographs have showed clearly that the characteristics of earthquake ground motion are greatly effected due to earthquake source processes, seismic wave propagation from source to site, deep subsurface structure in the concerned district and local site conditions. The lessons learned from these recent earthquakes have promoted the developments in the methods of evaluation of intensity of earthquake ground motion to apply the seismic design of buildings. The many kinds of attenuation formulae have been proposed on the basis of the data set of many strong motion accelerograms in the recent destructive earthquakes, and the methods of ground motion simulations have been studied on the theories of physical state on seismic fault, rupture process of seismic source, and wave propagation. Then, the current trends and ideas of evaluation of seismic load, design spectrum or ground motion time histories for response analyses, and new representation of intensity of earthquake ground motion to buildings by “energy spectrum” are discussed in this paper.

Innovative seismic design aspects of the Intermountain Power Project Converter Stations

Seismic designer requirements for the Intermountain Power Project Converter Station at Adelanto, California, were among the most stringent ever imposed. The project design criteria for critical HVDC components called for the use of a 0.5 g design ground acceleration. A report is presented on the seismic design of two such components: the thyristor valves and the large bushings. Innovative seismic design aspects include suspension of the thyristor valves from the roof of the valve hall and installation of a gimbal device to connect the bushings to their structural supports. Both schemes seismically isolated the equipment from the severest parts of the 0.5 g seismic design spectrum.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Innovative Seismic Design Aspects of the Intermountain Power Project Converter Stations

Seismic designer requirements for the Intermountain Power Project Converter Station at Adelanto, California, were among the most stringent ever imposed. The project design criteria for critical HVDC components called for the use of a 0.5 g design ground acceleration. A report is presented on the seismic design of two such components: the thyristor valves and the large bushings. Innovative seismic design aspects include suspension of the thyristor valves from the roof of the valve hall and installation of a gimbal device to connect the bushings to their structural supports. Both schemes seismically isolated the equipment from the severest parts of the 0.5 g seismic design spectrum. >

The Mexico Earthquake of September 19, 1985—Design Spectra for Mexico's Federal District

We describe the methods used to obtain seismic design spectra adopted for different zones of Mexico's Federal District in 1987 Building Code. Paper exposes the two approaches followed in the study, deterministic and probabilistic. The assumptions adopted are presented and justified. Several aspects that require detailed scrutiny are pointed out.

Development of stochastic ground movement: study on SMART-1 array data

The purpose of this paper is to estimate the possible effects of the source as well as the local soil characteristics on the spectral characteristics of ground motions. A stochastic soil amplification function was first developed. The parameters that control the spectral shape of ground motion were depth of soil deposit, soil density and shear modulus, corner frequency of the source as well as the high frequency decay rate of acceleration. The result of the model was compared to the data record by SMART-1 array. The development of seismic design spectrum was also discussed based on the proposed ground motion model. It is concluded that the local soil density, depth of soil deposit and the source corner frequency are the most significant factors to the influence of design spectrum. With the proposed ground motion model, a method to predict the design spectrum for a given earthquake magnitude can be constructed.

Standardized seismic design spectra for nuclear plant equipment

Standardized seismic design spectra were developed for the nuclear plant equipment. Such standardized spectra will reduce unnecessary spectrum computation for the individual plants as well as expedite the selection, purchase and qualification of equipment. Most attractive of all, standard equipment such as electric components can be conservatively qualified just once and then used by all plants located in the same seismic zones. Presented here are idealized design spectrum peak envelopes for different types of structure materials and for both the SSE and OBE conditions. Procedures are also provided for the application of the design spectrum peak envelopes to the seismic qualification of equipment either by dynamic analysis or testing.

Seismic design spectra and mapping procedures using hazard analysis based directly on oscillator response

AbstractThe calculation of design spectra for building sites threatened by seismic ground motion is approached by considering the maximum responses of linearly elastic oscillators as indicators of ground motion intensity. Attenuation functions describing the distribution of response as a function of earthquake magnitude and distance are derived using 68 components of recorded ground motion as data. With a seismic hazard analysis for several hypothetical building sites, the distributions of maximum oscillator responses to earthquakes of random magnitude and location are calculated, and spectra are drawn to indicate the maximum responses associated with specified probability levels. These spectra are compared to design spectra calculated from published methods of amplifying peak ground motion parameters. The latter spectra are found to be inconsistent in terms of risk for building sites very close and very far from faults. A ground motion parameter defined to be proportional to the maximum response of a 1 Hz, 2 per cent damped linearly elastic oscillator is investigated; this parameter, in conjunction with peak ground acceleration, is found to lead to risk‐consistent design spectra. Through these two parameters, a design earthquake magnitude and design hypocentral distance are defined, for a specified building site and risk level. The use of these parameters in the seismic hazard mapping of a region is illustrated.