• Earthquakes and Structures
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• v.6 no.2
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• pp.141-161
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• 2014

This article presents a new generation of empirical ground motion models for the prediction of response spectral accelerations in soil conditions, specifically developed for the Vrancea intermediate-depth seismic source. The strong ground motion database from which the ground motion prediction model is derived consists of over 800 horizontal components of acceleration recorded from nine Vrancea intermediate-depth seismic events as well as from other seventeen intermediate-depth earthquakes produced in other seismically active regions in the world. Among the main features of the new ground motion model are the prediction of spectral ordinates values (besides the prediction of the peak ground acceleration), the extension of the magnitudes range applicability, the use of consistent metrics (epicentral distance) for this type of seismic source, the extension of the distance range applicability to 300 km, the partition of total standard deviation in intra- and inter-event standard deviations and the use of a national strong ground motion database more than two times larger than in the previous studies. The results suggest that this model is an improvement of the previous generation of ground motion prediction models and can be properly employed in the analysis of the seismic hazard of Romania.

• Earthquakes and Structures
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• v.2 no.4
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• pp.357-376
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• 2011

Ground motion models predict the mean and standard deviation of the logarithm of spectral acceleration, as a function of predictor variables such as earthquake magnitude, distance and site condition. Such models have been developed for a variety of seismic environments throughout the world. Some calculations, such as the Conditional Mean Spectrum calculation, use this information but additionally require knowledge of correlation coefficients between logarithmic spectral acceleration values at multiple periods. Such correlation predictions have, to date, been developed primarily from data recorded in the Western United States from active shallow crustal earthquakes. This paper describes results from a study of spectral acceleration correlations from Japanese earthquake ground motion data that includes both crustal and subduction zone earthquakes. Comparisons are made between estimated correlations for Japanese response spectral ordinates and correlation estimates developed from Western United States ground motion data. The effect of ground motion model, earthquake source mechanism, seismic zone, site conditions, and source to site distance on estimated correlations is evaluated and discussed. Confidence intervals on these correlation estimates are introduced, to aid in identifying statistically significant differences in correlations among the factors considered. Observed general trends in correlation are similar to previous studies, with the exception of correlation of spectral accelerations between orthogonal components, which is seen to be higher here than previously observed. Some differences in correlations between earthquake source zones and earthquake mechanisms are observed, and so tables of correlations coefficients for each specific case are provided.

• Earthquakes and Structures
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• v.10 no.1
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• pp.105-123
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• 2016

In this paper, using the probabilistic methods, the seismic demand of buckling restrained braced frames subjected to earthquake was evaluated. In this regards, 4, 6, 8, 10, 12 and 14-storybuildings with different buckling restrained brace configuration (including diagonal, split X, chevron V and Inverted V bracings) were designed. Because of the inherent uncertainties in the earthquake records, incremental dynamical analysis was used to evaluate seismic performance of the structures. Using the results of incremental dynamical analysis, the "capacity of a structure in terms of first mode spectral acceleration", "fragility curve" and "mean annual frequency of exceeding a limit state" was determined. "Mean annual frequency of exceeding a limit state" has been estimated for immediate occupancy (IO) and collapse prevention (CP) limit states using both Probabilistic Seismic Demand Analysis (PSDA) and solution "based on displacement" in the Demand and Capacity Factor Design (DCFD) form. Based on analysis results, the inverted chevron (${\Lambda}$) buckling restrained braced frame has the largest capacity among the considered buckling restrained braces. Moreover, it has the best performance among the considered buckling restrained braces. Also, from fragility curves, it was observed that the fragility probability has increased with the height.

• Earthquakes and Structures
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• v.11 no.3
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• pp.505-516
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• 2016

This paper evaluates the scaling of ground motions recorded from nine intermediate-depth earthquakes produced in the Vrancea seismic zone in Romania. The considered ground motion database consists of 363 horizontal recordings obtained on soil classes B and C (according to Eurocode 8). An analysis of the inter- and intra-event spectral accelerations is performed in order to gain information regarding the magnitude and distance scaling of the Vrancea ground motions. The analyses reveal a significant influence of the earthquake magnitude and focal depth on the distance scaling and different magnitude and distance scaling for the two soil classes. A linear magnitude and distance scaling is inferred from the results for the range of magnitudes $5.2{\leq}M_W{\leq}7.1$. The results obtained are checked through stochastic simulations and the influence of the stress drop and kappa values on the ground motion levels is assessed. In addition, five ground motion models which were tested in other studies using recordings from Vrancea earthquakes are analyzed in order to evaluate their corresponding host stress drop and kappa. The results show generally a direct connection between the host kappa values and the host stress drop values. Moreover, all the ground motion models depict magnitude dependent host kappa and stress drop levels.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.5
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• pp.992-1002
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• 1988

The dynamic response of rotor-bearing systems subjected to six-component nonststionary earthquake ground accelerations is analyzed. The governing equations of motion for the rotor are derived using Lagrangian approach. The six-component earthquake inputs result in both inhomogeneous and parametric excitations, so that the conventional spectral analysis of random vibration is not applicable. The method of Monte Carlo simulation is utilized to simulate the six-component nonstationary earthquake ground motions and to determine the response statistics of rotor-bearing systems. The significant influences due to rotational motions of seismic base on the overall structural response is demonstrated by a numerical example.

• Journal of the Earthquake Engineering Society of Korea
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• v.26 no.6
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• pp.237-246
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• 2022

Based on the random-vibration-theory methodology, dynamic responses of nuclear facilities subjected to obliquely incidental and incoherent earthquake ground motions are calculated. The spectral power density functions of the 6-degree-of-freedom motions of a rigid foundation due to the incoherent ground motions are obtained with the local wave scattering and wave passage effects taken into consideration. The spectral power density function for the pseudo-acceleration of equipment installed on a structural floor is derived. The spectral acceleration of the equipment or the in-structure response spectrum is then estimated using the peak factors of random vibration. The approach is applied to nuclear power plant structures installed on half-spaces, and the reduction of high-frequency earthquake responses due to obliquely incident incoherent earthquake ground motions is examined. The influences of local wave scattering and wave passage effects are investigated for three half-spaces with different shear-wave velocities. When the shear-wave velocity is sufficiently large like hard rock, the local wave scattering significantly affects the reduction of the earthquake responses. In the cases of rock or soft rock, the earthquake responses of structures are further affected by the incident angles of seismic waves or the wave passage effects.

• Structural Engineering and Mechanics
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• v.26 no.6
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• pp.687-707
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• 2007

High-tech facilities engaged in the production of semiconductors and optical microscopes are extremely expensive, which may require time-domain analysis for seismic resistant design in consideration of the most critical directions of seismic ground motions. This paper presents a framework for generating three-dimensional critical seismic ground acceleration time histories compatible with the response spectra specified in seismic design codes. The most critical directions of seismic ground motions associated with the maximum response of a high-tech facility are first identified. A new numerical method is then proposed to derive the power spectrum density functions of ground accelerations which are compatible with the response spectra specified in seismic design codes in critical directions. The ground acceleration time histories for the high-tech facility along the structural axes are generated by applying the spectral representation method to the power spectrum density function matrix and then multiplied by envelope functions to consider nonstationarity of ground motions. The proposed framework is finally applied to a typical three-story high-tech facility, and the numerical results demonstrate the feasibility of the proposed approach.

• Earthquakes and Structures
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• v.12 no.2
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• pp.177-189
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• 2017

For energy-based seismic design, a simplified normalized cumulative hysteretic energy spectrum proposed for obtaining hysteretic energy as energy demand is the main objective in this paper. The dimensionless parameter, ${\beta}_{Eh}$, is presented to express hysteretic energy indirectly. The ${\beta}_{Eh}$ spectrum is constructed directly through subtracting the hysteretic energy of single degree-of-freedom (SDOF) system energy equation. The simplified ${\beta}_{Eh}$ spectral formulation as well as pseudo-acceleration spectrum of modern seismic provisions is developed based on the regression analysis of the large number of seismic responses of SDOF system subjected to earthquake excitations, which considers the influence of earthquake event, soil type, damping ratio, and ductility factor. The relationship between PGV and PGA is established according to the statistical analysis relied on a total of 422 ground motion records. The combination of ${\beta}_{Eh}$ spectrum and PGV/PGA equation allows determining the cumulative hysteretic energy as a main aseismic design indicator.

• Earthquakes and Structures
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• v.5 no.1
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• pp.1-22
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• 2013

Soft storey failure mechanism is a common collapse mode for masonry-infilled (MI) reinforced concrete (RC) buildings subjected to severe earthquakes. Simple analytical equations correlating global with local ductility demands are derived from pushover (PO) analyses for seismic assessments of regular MI RC frames, considering the critical interstorey drift ratio, number of storeys and lateral loading configurations. The reliability of the equations is investigated using incremental dynamic analyses for MI RC frames of up to 7 storeys. Using the analytical ductility relationship and a coefficient-based method (CBM), the response spectral accelerations and period shift factors of low-rise MI RC frames are computed. The results are verified through published shake table test results. In general applications, the analytical ductility relationships thus derived can be used to bypass the onerous PO analysis while accurately predicting the local ductility demands for seismic assessment of regular MI RC frames.

• Structural Engineering and Mechanics
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• v.20 no.5
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• pp.527-542
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• 2005

The main objective of this study is to examine the accuracy of the complete quadratic combination (CQC) rule with the modal responses defined by the ordinates of the uniform hazard spectra (UHS) to evaluate the peak responses of the multi-degree-of-freedom (MDOF) systems subjected to nonstationary seismic excitations. For the probabilistic analysis of the peak responses, it is considered that the seismic excitations can be modeled using evolutionary power spectra density functions with uncertain model parameters. More specifically, a seismological model and the Kanai-Tajimi model with the boxcar or the exponential modulating functions were used to define the evolutionary power spectral density functions in this study. A set of UHS was obtained based on the probabilistic analysis of transient responses of single-degree-of-freedom systems subjected to the seismic excitations. The results of probabilistic analysis of the peak responses of MDOF systems were obtained, and compared with the peak responses calculated by using the CQC rule with the modal responses given by the UHS. The comparison seemed to indicate that the use of the CQC rule with the commonly employed correlation coefficient and the peak modal responses from the UHS could lead to significant under- or over-estimation when contributions from each of the modes are similarly significant.