• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.4
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• pp.8-14
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• 2017

Nonstructural components, such as electrical equipment, have critical roles in the proper functionality of various infrastructure systems. Some of these devices in certain facilities should operate even under strong seismic shaking. However, it is challenging to define each mechanical and operational failure and determine system failure probabilities under seismic shaking due to the uncertainties in earthquake excitations and the diversity of electrical equipment, among other factors. Therefore, it is necessary to develop effective and practical probabilistic models for performance assessment of electrical equipment considering variations in equipment features and earthquakes. This study will enhance the understanding of the effect of rocking behavior on nonstructural equipment, and linear-to-nonlinear behavior of restrainers. In addition, this study will generate probabilistic seismic demand models of rigid equipment for a set of conventional and novel intensity measures.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.65-72
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• 2018

Seismically induced settlement exceeding dam freeboard may lead to a dam failure. The prediction of settlement is important also because it is also reported to be strongly related to longitudinal crack width and depth, which are critical indices used for safe evaluation of dams. The empirical correlation derived from numerical simulations is most often used. In this study, two-dimensional dynamic nonlinear analyses are performed using representative CFRD and ECRD fill dams. A total of 20 recorded motions are used to account for the influence on ground motion intensity and magnitude. The calculated crest settlements are correlated to four ground motion parameters, which are peak ground acceleration (PGA), peak ground velocity (PGV), Aria Intensity ($I_A$), and magnitude. It is demonstrated that using ground motion parameters in addition to PGA can significantly increase the prediction accuracy.

• Earthquakes and Structures
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• v.7 no.6
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• pp.1001-1024
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• 2014

The size of spread footings was found to be unnecessarily large from some actual engineering practices constructed in Taiwan, due to the strict design provisions related to footing uplift. According to the earlier design code in Taiwan, the footing uplift involving separation of footing from subsoil was permitted to be only up to one-half of the foundation base area, as the applied moment reaches the value of plastic moment capacity of the column. The reason for this provision was that rocking of spread footings was not a favorable mechanism. However, recent research has indicated that rocking itself may not be detrimental to seismic performance and, in fact, may act as a form of seismic isolation mechanism. In order to clarify the effects of the relative strength between column and foundation on the rocking behavior of a column, six circular reinforced concrete (RC) columns were designed and constructed and a series of rocking experiments were performed. During the tests, columns rested on a rubber pad to allow rocking to take place. Experimental variables included the dimensions of the footings, the strength and ductility capacity of the columns and the intensity of the applied earthquake. Experimental data for the six circular RC columns subjected to quasi-static and pseudo-dynamic loading are presented. Results of each cyclic loading test are compared against the benchmark test with fixed-base conditions. By comparing the experimental responses of the specimens with different design details, a key parameter of rocking behavior related to footing size and column strength is identified. For a properly designed column with the parameter higher than 1, the beneficial effects of rocking in reducing ductility and the strength demand of columns is verified.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.179-186
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• 2020

Investigating damage potential of the railway infrastructure requires either large amount of case histories or in-depth numerical analyses, or both for which large amounts of effort and time are necessary to accomplish thoroughly. Rather than performing comprehensive studies for each damage case, in this study we collect and analyze a case history of the high-speed railway system damaged by the 2004 M6.6 Niigata Chuetsu earthquake for the development of the seismic fragility curve. The development processes are: 1) slice the railway system as 200 m segments and assigned damage levels and intensity measures (IMs) to each segment; 2) calculate probability of damage for a given IM; 3) estimate fragility curves using the maximum likelihood estimation regression method. Among IMs considered for fragility curves, spectral acceleration at 3 second period has the most prediction power for the probability of damage occurrence. Also, viaduct-type structure provides less scattered probability data points resulting in the best-fitted fragility curve, but for the tunnel-type structure data are poorly scattered for which fragility curve fitted is not meaningful. For validation purpose fragility curves developed are applied to the 2016 M7.0 Kumamoto earthquake case history by which another high-speed railway system was damaged. The number of actual damaged segments by the 2016 event is 25, and the number of equivalent damaged segments predicted using fragility curve is 22.21. Both numbers are very similar indicating that the developed fragility curve fits well to the Kumamoto region. Comparing with railway fragility curves from HAZUS, we found that HAZUS fragility curves are more conservative.

• 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.

• Journal of Korean Association for Spatial Structures
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• v.14 no.1
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• pp.77-84
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• 2014

Simple 3, 10, and 30-story buildings with a nonstructural element which is located at roof or near the middle of the building height are selected. Based on 2009 Korean Building Code, the seismic design force applied at the nonstructural element is evaluated. Response spectrum analysis is conducted with the design response acceleration spectrum of 2009 Korean Building Code and the analytical response is compared with the seismic design force from the Code. Furthermore, an artificial earthquake based on Korean design response acceleration spectrum and the 50% intensity of El Centro earthquake, which can be considered as the maximum future earthquake possibly occurring in Korea, are selected to conduct time history analysis. When the period of the nonstructural element is shorter than 0.06 second or longer than that of the 1st period of each building, the Code equations of seismic design force for nonstructural element seems to be appropriate. However, the period of the nonstructural element is close to the one of the building's higher mode periods including the 1st period, seismic force of the nonstructural element might exceed the Code specified seismic design force.

• Structural Engineering and Mechanics
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• v.40 no.4
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• pp.517-539
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• 2011

This paper presents the seismic responses of a 1:5-scale five-story reinforced concrete building model, which represents a residential apartment building that has a high irregularity of weak story, soft story, and torsion simultaneously at the ground story. The model was subjected to a series of uni- and bi-directional earthquake simulation tests. Analysis of the test results leads to the following conclusions: (1) The model survived the table excitations simulating the design earthquake with the PGA of 0.187 g without any significant damages, though it was not designed against earthquakes; (2) The fundamental mode was the torsion mode. The second and third orthogonal translational modes acted independently while the torsion mode showed a strong correlation with the predominant translational mode; (3) After a significant excursion into inelastic behavior, this correlation disappeared and the maximum torsion and torsion deformation remained almost constant regardless of the intensity of the two orthogonal excitations; And, (4) the lateral resistance and stiffness of the critical columns and wall increased or decreased significantly with the large variation of acting axial forces caused by the high bi-directional overturning moments and rocking phenomena under the bi-directional excitations.

• Journal of the Korean Geotechnical Society
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• v.20 no.7
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• pp.33-44
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• 2004

This paper is focused on the spatial variability of measured strong motion data during earthquake and its relationship with the performance of water distribution pipelines and residential buildings. Analyses of strong motion and the correlations of peak ground velocity (PGV) and pipeline and building damage were conducted with a very large geographical information system (GIS) database including the relationship of time and earthquake intensity and the measured location, and Kriging spatial statistics. Kriging was used to develop regressions of pipeline repair rate (RR) and residential building damage ratio (DR) associated with $90\%$ confidence peak ground velocity (PGV). Such regressions using Kriging provide an explicit means of characterizing the uncertainty embodied in the strong motion data compared with other spacial statistics such as inverse distance method.

• Earthquakes and Structures
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• v.18 no.2
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• pp.163-170
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• 2020

Floor acceleration plays a major role in the seismic design of nonstructural components and equipment supported by structures. Large floor acceleration may cause structural damage to or even collapse of buildings. For precision instruments in high-tech factories, even small floor accelerations can cause considerable damage in this study. Six P-wave parameters, namely the peak measurement of acceleration, peak measurement of velocity, peak measurement of displacement, effective predominant period, integral of squared velocity, and cumulative absolute velocity, were estimated from the first 3 s of a vertical ground acceleration time history. Subsequently, a new predictive algorithm was developed, which utilizes the aforementioned parameters with the floor height and fundamental period of the structure as the new inputs of a support vector regression model. Representative earthquakes, which were recorded by the Structure Strong Earthquake Monitoring System of the Central Weather Bureau in Taiwan from 1992 to 2016, were used to construct the support vector regression model for predicting the peak floor acceleration (PFA) of each floor. The results indicated that the accuracy of the predicted PFA, which was defined as a PFA within a one-level difference from the measured PFA on Taiwan's seismic intensity scale, was 96.96%. The proposed system can be integrated into the existing earthquake early warning system to provide complete protection to life and the economy.

• Nuclear Engineering and Technology
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• v.46 no.5
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• pp.699-706
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• 2014

The probabilistic seismic performance of a standard Korean nuclear power plant (NPP) with an idealized isolation is investigated in the present work. A probabilistic seismic hazard analysis (PSHA) of the Wolsong site on the Korean peninsula is performed by considering peak ground acceleration (PGA) as an earthquake intensity measure. A procedure is reported on the categorization and selection of two sets of ground motions of the Tohoku earthquake, i.e. long-period and common as Set A and Set B respectively, for the nonlinear time history response analysis of the base-isolated NPP. Limit state values as multiples of the displacement responses of the NPP base isolation are considered for the fragility estimation. The seismic risk of the NPP is further assessed by incorporation of the rate of frequency exceedance and conditional failure probability curves. Furthermore, this framework attempts to show the unacceptable performance of the isolated NPP in terms of the probabilistic distribution and annual probability of limit states. The comparative results for long and common ground motions are discussed to contribute to the future safety of nuclear facilities against drastic events like Tohoku.