Shape Of Response Spectra Research Articles

Characteristics of Spectral Matched Ground Motions Time Histories According to Seed Ground Motion Selection

According to several seismic design standards, a ground motion time history should be selected similar to the design response spectrum, or a ground motion time history should be modified by matching procedure to the design response spectrum through the time-domain method. For the response spectrum matching procedure, appropriate seed ground motions need to be selected to maintain recorded earthquake accelerogram characteristics. However, there are no specific criteria for selecting the seed ground motions for applying this methodology. In this study, the characteristics of ground motion time histories between seed motions and spectral matched motions were compared. Intensity measures used in the design were compared, and their change by spectral matching procedure was quantified. In addition, the seed ground motion sets were determined according to the response spectrum shape, and these sets analyzed the response of nonlinear and equivalent linear single degrees of freedom systems to present the seed motion selection conditions for spectral matching. As a result, several considerations for applying the time domain spectral matching method were presented.

Plasmonic-Layered InAs/InGaAs Quantum-Dots-in-a-Well Pixel Detector for Spectral-Shaping and Photocurrent Enhancement.

The algorithmic spectrometry as an alternative to traditional approaches has the potential to become the next generation of infrared (IR) spectral sensing technology, which is free of physical optical filters, and only a very small number of data are required from the IR detector. A key requirement is that the detector spectral responses must be engineered to create an optimal basis that efficiently synthesizes spectral information. Light manipulation through metal perforated with a two-dimensional square array of subwavelength holes provides remarkable opportunities to harness the detector response in a way that is incorporated into the detector. Instead of previous experimental efforts mainly focusing on the change over the resonance wavelength by tuning the geometrical parameters of the plasmonic layer, we experimentally and numerically demonstrate the capability for the control over the shape of bias-tunable response spectra using a fixed plasmonic structure as well as the detector sensitivity improvement, which is enabled by the anisotropic dielectric constants of the quantum dots-in-a-well (DWELL) absorber and the presence of electric field along the growth direction. Our work will pave the way for the development of an intelligent IR detector, which is capable of direct viewing of spectral information without utilizing any intervening the spectral filters.

Variable vs. invariable elastic response spectrum shapes: impact on the mean annual frequency of exceedance of limit states

In research studies focusing on the evaluation of the fragility function of buildings, numerical analyses are almost always carried out using a single suite of accelerograms, which is scaled in intensity to simulate earthquakes of different magnitude.Therefore, such numerical analyses usually neglect the effects of the variation of important seismological characteristics, e.g. the shape of the pseudo-acceleration response spectrum, on the structural response.To evaluate the impact of the variation of the elastic response spectrum shape with the selected earthquake return period on the mean annual frequency of exceedance of assigned limit state functions, the response of a large set of systems is determined in this paper by two different methods of analysis. In the first method of analysis, a multiple stripe analysis is carried out with accelerograms characterised by median response spectrum shape and ground motion duration variable with the earthquake intensity measure. The information pertaining the probabilistic description of the acceleration spectra has been obtained from the website of the National Institute of Geophysics and Volcanology for the Italian territory, whereas the one regarding the earthquake duration has been derived from semi-empirical relationships reported in the literature. In the second method of analysis, instead, the accelerograms are characterized by median response spectrum shape and ground motion duration invariable with the intensity measure.Finally, to evaluate the influence of the scattering of the spectral responses about their mean value, a third analysis is carried out by means of a set of artificial accelerograms with response spectra that are characterized by virtually zero standard deviation and spectrum shape and ground motion duration invariable with the magnitude of the earthquake.To increase the relevance of the results, the investigated systems include single-degree-of–freedom systems with degrading or non-degrading inelastic response and reinforced concrete and steel multi-degree of freedom systems.

A Shape of the Response Spectrum for Evaluation of the Ultimate Seismic Capacity of Structures and Equipment including High-frequency Earthquake Characteristics

In 2016, an earthquake occurred at Gyeongju, Korea. At the Wolsong site, the observed peak ground acceleration was lower than the operating basis earthquake (OBE) level of Wolsong nuclear power plant. However, the measured spectral acceleration value exceeded the spectral acceleration of the operating-basis earthquake (OBE) level in some sections of the response spectrum, resulting in a manual shutdown of the nuclear power plant. Analysis of the response spectra shape of the Gyeongju earthquake motion showed that the high-frequency components are stronger than the response spectra shape used in nuclear power plant design. Therefore, the seismic performance evaluation of structures and equipment of nuclear power plants should be made to reflect the characteristics of site-specific earthquakes. In general, the floor response spectrum shape at the installation site or the generalized response spectrum shape is used for the seismic performance evaluation of structures and equipment. In this study, a generalized response spectrum shape is proposed for seismic performance evaluation of structures and equipment for nuclear power plants. The proposed response spectrum shape reflects the characteristics of earthquake motion in Korea through earthquake hazard analysis, and it can be applied to structures and equipment at various locations.

Spectral Shape in Accordance with the Magnitude and Distance of Earthquakes and Its Effect on Multi-DOF Structures

In this study earthquake records were collected for rock conditions that do not reflect seismic amplification by soil from global earthquake databases such as PEER, USGS, and ESMD. The collected earthquake records were classified and analyzed based on the magnitude and distance of earthquakes. Based on the analyzed earthquakes, the design response spectrum shape, effective ground acceleration, and amplification ratios for each period band are presented. In addition, based on the analyzed data, the story shear force for 5F, 10F, 15F, and 20F were derived through an analysis of the elastic time history for multi-DOF structures. The results from analyzing the rock earthquake record show that the seismic load tends to be amplified greatly in the short period region, which is similar to results observed from the Gyeongju and Pohang earthquakes. In addition, the results of the multi-DOF structure analysis show that existing seismic design criteria can be underestimated and designed in the high-order mode of short- and medium-long cycle structures.

A response spectrum-based indicator for structural damage prediction

Improving predictive relationships between strong ground motion and seismically induced damage in buildings is an important topic for seismic risk assessment. Spectral acceleration at a structure’s fundamental period Sa(T1) has often been used as the indicator of the potential damage a given ground motion may induce on structural systems. However, such a scalar indicator (Damage Potential Indicator, DPI) captures only limited information about the ground motion time history and response spectrum shape. In a severely damaged state, the effective period of a structure will change, which makes the structure respond to other parts of the response spectrum. In this study, a new response spectrum-based DPI that contains an intensity component and a spectral shape component is proposed. The critical period range of the response spectrum that should be considered in spectral shape evaluation is determined using a circle rule for bilinear single-degree-of-freedom (SDOF) systems. The effectiveness of the newly proposed DPI is validated by comparing damage potential similarity using a database of ground motion records.

On selection and scaling of ground motions for analysis of seismically isolated structures

A broader consensus on the number of ground motions to be used and the method of scaling to be adopted for nonlinear response history analysis (RHA) of structures is yet to be reached. Therefore, in this study, the effects of selection and scaling of ground motions on the response of seismically isolated structures, which are routinely designed using nonlinear RHA, are investigated. For this purpose, isolation systems with a range of properties subjected to bidirectional excitation are considered. Benchmark response of the isolation systems is established using large sets of unscaled ground motions systematically categorized into pulse-like, non-pulse-like, and mixed set of motions. Different subsets of seven to 14 ground motions are selected from these large sets using (a) random selection and (b) selection based on the best match of the shape of the response spectrum of ground motions to the target spectrum. Consequences of weighted scaling (also commonly referred to as amplitude scaling or linear scaling) as well as spectral matching are investigated. The ground motion selection and scaling procedures are evaluated from the viewpoint of their accuracy, efficiency, and consistency in predicting the benchmark response. It is confirmed that seven time histories are sufficient for a reliable prediction of isolation system displacement demands, for all ground motion subsets, selection and scaling procedures, and isolation systems considered. If ground motions are selected based on their best match to the shape of the target response spectrum (which should be preferred over randomly selected motions), weighted scaling should be used if pulse-like motions are considered, either of weighted scaling or spectral matching can be used if non-pulse-like motions are considered, and an average of responses from weighted-scaled and spectrum-matched ground motions should be used for a mixed set of motions. On the other hand, the importance of randomly selected motions in representing inherent variability of response is recognized and it is found that weighted scaling is more appropriate for such motions.

Comparison of seismic design for steel moment frames in Europe, the United States, Japan and China

Seismic provisions to guide the design of steel moment frames in Europe, the United States, Japan and China are comprehensively examined. Seismic hazard levels and performance requirements, ground type classification, magnitude and shape of elastic response spectra, seismic design force and distribution of required story shear strength, local ductility requirements, and reduction factors are compared. The results show that the no-collapse requirements in Eurocode and Japanese code correspond to a lower level of ground motion than the other two codes. The unreduced elastic response spectra given in four codes are quite different in recognition of different ground types and seismicity, in particular, Japanese code generally specifies much larger elastic spectrum than other codes. Although local ductility requirements are quite similar, U.S. code specifies higher reduction factors than Eurocode and Japanese code, while Chinese code stipulates a constant reduction factor with a relatively small value regardless of the ductility level of structures. As a result of such over-conservatism, Chinese code designed steel moment frames exhibit 20% to 150% larger lateral stiffness and resistance than Eurocode and U.S. code in most cases, while the significant even larger lateral stiffness and resistance predicted by Japanese code than that by Chinese code is mainly due to the larger seismic force from elastic response spectrum.

Ductility‐dependent intensity measure that accounts for ground‐motion spectral shape and duration

SummaryThe calculated nonlinear structural responses of a building can vary greatly, even if recorded ground motions are scaled to the same spectral acceleration at a building's fundamental period. To reduce the variation in structural response at a particular ground‐motion intensity, this paper proposes an intensity measure (IMcomb) that accounts for the combined effects of spectral acceleration, ground‐motion duration, and response spectrum shape. The intensity measure includes a new measure of spectral shape that integrates the spectrum over a period range that depends on the structure's ductility. The new IM is efficient, sufficient, scalable, transparent, and versatile. These features make it suitable for evaluating the intensities of measured and simulated ground motions.The efficiency and sufficiency of the new IM is demonstrated for the following: (i) elastic‐perfectly plastic single‐degree‐of‐freedom (SDOF) oscillators with a variety of ductility demands and periods; (ii) ductile and brittle deteriorating SDOF systems with a variety of periods; and (iii) collapse analysis for 30 previously designed frames. The efficiency is attributable to the inclusion of duration and to the ductility dependence of the spectral shape measure. For each of these systems, the transparency of the intensity measure made it possible to identify the sensitivity of structural response to the various characteristics of the ground motion. Spectral shape affected all structures, but in particular, ductile structures. Duration only affected structures with cyclic deterioration. Copyright © 2015 John Wiley & Sons, Ltd.

A time–frequency approach for generation of synthetic time-histories of earthquake signals

Seismic signals are non-stationary in nature, generated by earthquake and some other sources like explosive, landslides etc. In this paper, pattern of time varying frequency components of real-time recorded data of seismic signal are investigated by computing the mean of Gabor transform. In most of the cases, it is not possible to use recorded data of strong ground motion at a given site. It is therefore essential to analyze synthetic time-history which gives the prediction of strong ground motion in the regions where actual records can’t be used. In this work, the problem has been shown in synthetic time-histories where time–frequency variation is not controlled and suggested Gabor transformation based approach for generation of site specific synthetic time-history having control on time–frequency variation. Synthetic time-histories have been generated at five different sites by computing the average of Gabor transform of eight records for different earthquakes at each site. It is also shown that shape of response spectrum calculated from the generated synthetic time-history at each site is quite comparable to shape of mean response spectrum of recorded time-histories. Synthetic time-histories of a realistic time–frequency variation will be very useful for the researchers who wish to perform the nonlinear analysis of structures for a particular site.

A Study of the Sensitivity of Response Spectral Amplitudes on Seismological Parameters Using Algorithmic Differentiation

Abstract Response spectra are of fundamental importance in earthquake engineering and represent a standard measure in seismic design for the assessment of structural performance. However, unlike Fourier spectral amplitudes, the relationship of response spectral amplitudes to seismological source, path, and site characteristics is not immediately obvious and might even be considered counterintuitive for high oscillator frequencies. The understanding of this relationship is nevertheless important for seismic‐hazard analysis. The purpose of the present study is to comprehensively characterize the variation of response spectral amplitudes due to perturbations of the causative seismological parameters. This is done by calculating the absolute parameter sensitivities (sensitivity coefficients) defined as the partial derivatives of the model output with respect to its input parameters. To derive sensitivities, we apply algorithmic differentiation (AD). This powerful approach is extensively used for sensitivity analysis of complex models in meteorology or aerodynamics. To the best of our knowledge, AD has not been explored yet in the seismic‐hazard context. Within the present study, AD was successfully implemented for a proven and extensively applied simulation program for response spectra (Stochastic Method SIMulation [SMSIM]) using the TAPENADE AD tool. We assess the effects and importance of input parameter perturbations on the shape of response spectra for different regional stochastic models in a quantitative way. Additionally, we perform sensitivity analysis regarding adjustment issues of ground‐motion prediction equations.

Displacement-Based Fragility Curves for Seismic Assessment of Adobe Buildings in Cusco, Peru

The seismic vulnerability of single-story adobe dwellings located in Cusco, Peru, is studied based on a mechanics-based procedure, which considers the analysis of in-plane and out-of-plane failure mechanisms of walls. The capacity of each dwelling is expressed as a function of its displacement capacity and period of vibration and is evaluated for different limit states to damage. The seismic demand has been obtained from several displacement response spectral shapes. From the comparison of the capacity with the demand, probabilities of limit state exceedance have been obtained for different PGA values. The results indicate that fragility curves in terms of PGA are strongly influenced by the response spectrum shape; however, this is not the case for the derivation of fragility curves in terms of limit state spectral displacement. Finally, fragility curves for dwellings located in Pisco, Peru, were computed and the probabilities of limit state exceedance were compared with the data obtained from the 2007 Peruvian earthquake.

지진기록 사용에 따른 고층 면진건물의 동적 응답

The purpose of this study is to evaluate seismic capacity of seismically isolated building according to the earthquake motion record selection method. To analyze the seismic behavior, 20-story building is designed, which has base isolation system. The using earthquake motion record were selected by two categories. The one is a proposed earthquake record according to soil type and response spectrum shape, and the other is a well known earthquake events such as El Centro (1940). The time history analysis results of base isolation buildings be induced difference results according to each ground motion records. Therefore detailed guidelines for the ground motion records selection method must be prepared. And the response of isolation story displacement and shear force show good seismic performance in consideration of the proposed earthquake records.

Risk-oriented seismic microzoning study of an urban settlement

A methodology is presented to evaluate the local seismic response of an urbanized site and to realize cost-effective seismic microzoning studies on a quantitative basis with the aim to provide more insights for the choice of risk mitigation measures. The methodology makes use of an integrated deterministic and probabilistic seismic hazard analysis to select the reference earthquake and the related ground motion used to assess the local seismic response. Amplified response spectra, related to local site effects, are obtained after the investigation of the local geological conditions carried out through integrated geological, geophysical and geotechnical surveys. The amplified response spectra are then converted into reference ones, to match the shape of conventional response spectra provided by many international seismic codes such as Eurocode 8 ( Design of structures for earthquake resistance). A vulnerability analysis provided the distribution of the buildings’ typology in the urban centre and allowed for computing the expected damages. The outcome is a zoning of the investigated site matching the correlation between the severity of the expected seismic actions as modified by the local seismic response and the structural features of the buildings present in the urban area. The resulting seismic microzoning is more informative than conventional ones, having the potential to be used for the adoption of risk mitigation measures such as the seismic retrofitting of buildings and the formulation of emergency plans for civil protection purposes.

Influence of the Sedimentary Cover in the Cologne Area on the Shape of Response Spectra

For the greater area of the city of Cologne a microzonation from an earthquake engineering perspective was introduced. The area has been divided into eight subregions with approximately uniform soil profile. For all regions the influence of the sediments on simulated earthquakes has been investigated by three well known methods: 2-layer solution, SHAKE 91, HASKELL matrix algorithm. The transfer functions and response spectra were computed and compared to the elastic acceleration response spectra of the German building code E-DIN 4149. Two different methods for the generation of synthetic accelerograms and the three wave propagation analysis procedures have been compared and a series of issues relevant to the practical application of them were discussed.

Comparison of European and Japanese seismic design of steel building structures

This paper compares EuroCode 8 (EC8) and the Japanese seismic design code (BCJ) for steel moment frames and braced frames. Soil classification, magnitude and shape of unreduced elastic response spectra, distribution of seismic shear along the height, member ductility requirements, and behavior factor are compared. It was found that the two codes are relatively similar except for the seismic force stipulated for the serviceability limit state. EC8 gives an approximately 2.5 times larger force for this limit state. Behavior factors that allow for system ductility are significantly different between the two codes; for moment frames BCJ is more conservative by about 50%. Strength demanded by EC8 and BCJ is evaluated for steel moment frames and chevron braced frames. Although the behavior factor is less conservative in EC8, the net strength required by EC8 is significantly greater than the corresponding BCJ strength for steel moment frames, and it occurs because of the significantly larger design force stipulated for serviceability in EC8. With regard to braced frames, BCJ leads to larger lateral story strength except for chevron braced frames with slender braces.

스펙트럼 형상이 원전 기기 지진취약도에 미치는 영향 평가

최근 수행된 우리나라 원전 부지에 대한 지진재해도 해석 결과 작성된 등재해도 스펙트럼에서 고진동수 성분의 지진동이 매우 우세하게 나타나고 있다. 일반적으로 지진취약도 해석에서는 설계 스펙트럼에 내재된 보수성을 평가하기 위해 스펙트럼 형상계수가 사용된다. 본 연구에서는 입력지반운동 스펙트럼의 형상이 변화함에 따른 층응답스펙트럼의 형상 변화를 분석하였다. 이때 입력 스펙트럼으로부터 직접 층응답스펙트럼을 작성할 수 있는 직접법을 사용하였다. 본 연구 결과 건물 내부에 설치된 기기의 취약도해석에서는 입력스펙트럼에 내재된 보수성을 구조물의 고유진동수에 대한 스펙트럼 형상계수가 아닌 기기의 고유진동수에 따른 층응답스펙트럼 형상계수로 고려하는 것이 정확한 취약도해석 결과를 주는 것으로 나타났다. The result of recent seismic hazard analysis indicates that the ground motion response spectra for Korean nuclear power plant site have relatively large frequency acceleration contents. In the ordinary seismic fragility analysis of nuclear power plant structures and equipments, the safety margin of design ground response spectrum is directly used as a response spectrum shape factor. The effects of input response spectrum shape on the floor response spectrum were investigated by performing the direct generation of floor response spectrum from the ground response spectrum. The safety margin included in the design ground response spectrum should be considered as a floor response spectrum shape factor for the seismic fragility analysis of the equipments located in a building.

모드기여도를 고려한 복수모드구조물의 지진취약도분석

이 연구는 원자력발전소 구조물의 확률론적 내진성능을 평가하는 수단으로 이용되고 있는 지진취약도분석 기법에 대하여 소개하고, 지진취약도분석에 입력자료로 제공되는 기본변수의 특성에 대하여 논의하였다. 특히, 지진취약도 분석결과에 지대한 영향을 미칠 수 있는 입력변수의 하나인 응답스펙트럼형태계수의 정의 방법을 개선하였다. 새로운 응답스펙트럼형태계수는 구조물의 고유진동모드별 기여도가 전체 구조응답에 미치는 영향을 고려할 수 있도록 모드별 기여도를 이용하여 표현하였다. 대표적인 원자력발전소 구조물을 대상으로 예제분석을 수행하고, 제안된 응답스펙트럼형태계수의 유용성 및 적용성을 검증하였다. 특히, 이 논문의 방법은 복합모드감쇠특성을 갖는 구조물의 경우에도 효과적으로 적용될 수 있음을 확인하였다. In the course of seismic probabilistic risk assessment(SPRA), seismic fragility analysis(SFA) is utilized as a tool to evaluate the actual seismic capacity of structures. This paper introduces a methodology of SFA and its evaluation procedures, especially focusing on the basic fragility variables. A new definition of the response spectrum shape factor as one of the most critical basic variables is suggested. The new factor is expressed as a term of linear algebraic sum using the modal contribution factor. The efficiency of new response spectrum shape factor is evaluated and validated to use in practice through the case study of the nuclear power plant structures. The case study results show that the proposed method can be effectively applicable to multi-mode structures with composite modal damping.

Influence of earthquake source parameters and damping on elastic response spectra for Iranian earthquakes

In this paper the influence of effective duration of strong motion, soil condition, magnitude and shape of accelerogram time history on the elastic response spectra has been investigated. A total of 106 of Iran's horizontal acceleration components of strong motion records are selected. These accelerograms are categorized based on their earthquake parameters and soil condition of recording station and the influence of different soil conditions are plotted in graphs. The influence of damping ratio on the response spectra is also investigated. Analytical results show that the influence of soil condition is significant for the shape of response spectra. The influence of effective duration of strong motion has been studied by definition based on the energy of the accelerogram. It can be seen that an increase in effective duration causes a reduction in the slope of response spectra in the long period part and increases the spectral values. The effect of damping on response spectra is represented by a special coefficient which depends on the period and damping of the structure and soil condition.

“Site & region-specific” response spectra: a probabilistic approach

Design seismic forces depend on Peak Ground Acceleration (PGA) values and on the shape of Response Spectrum (RS) curves dictated by Building Codes or which need to be evaluated in every particular case. The PGA values and RS curves strictly depend on earthquake magnitude and distance, as well as on the regional and local geological conditions. At present, there is no doubt that it is necessary to construct so-called “Site & Region-specific” Building Code provisions reflecting the influence of different magnitude events at different distances that may occur during the life time of the construction, as well as the variety of local ground conditions. A scheme of Uniform Hazard Response Spectra and PGA estimation considering local site response is described in this paper. The assessments of these design parameters are obtained on the basis of Uniform Hazard Fourier spectra using the conception of “dominant earthquakes”. The effect of local geology is included by means of the soil/reference site spectral ratios.