• Proceedings of the KIEE Conference
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• 2006.04a
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• pp.246-248
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• 2006

This paper is concerned with non-fragile guaranteed cost state feedback controller design algorithm for descriptor systems with time-varying delay and static state feedback controller with multiplicative uncertainty. The considered uncertainties are norm-bounded and time delay is time-varying. Under the condition of controller gain variations, conditions for the existence of controller satisfying asymptotic stability and non-fragility and controller design method are derived via LMI approach. Moreover, the measure of non-fragility and the upper bound to minimize guaranteed cost function are given.

• Earthquakes and Structures
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• v.14 no.3
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• pp.203-214
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• 2018

Predictive demand and collapse fragility functions are two essential components of the probabilistic seismic demand analysis that are commonly developed based on statistics with enormous, costly and time consuming data gathering. Although this approach might be justified for research purposes, it is not appealing for practical applications because of its computational cost. Thus, in this paper, Bayesian regression-based demand and collapse models are proposed to eliminate the need of time-consuming analyses. The demand model developed in the form of linear equation predicts overall maximum inter-story drift of the lowto mid-rise regular steel moment resisting frames (SMRFs), while the collapse model mathematically expressed by lognormal cumulative distribution function provides collapse occurrence probability for a given spectral acceleration at the fundamental period of the structure. Next, as an application, the proposed demand and collapse functions are implemented in a seismic fragility analysis to develop fragility and consequently seismic demand curves of three example buildings. The accuracy provided by utilization of the proposed models, with considering computation reduction, are compared with those directly obtained from Incremental Dynamic analysis, which is a computer-intensive procedure.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.6
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• pp.265-273
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• 2023

This study proposes a methodology for the regional seismic risk assessment of structural damage to buildings in Korea based on evaluating individual buildings, considering inconsistency between the administrative district border and grid lines to define seismic hazard. The accuracy of seismic hazards was enhanced by subdividing the current 2km-sized grids into ones with a smaller size. Considering the enhancement of the Korean seismic design code in 2005, existing seismic fragility functions for seismically designed buildings are revised by modifying the capacity spectrum according to the changes in seismic design load. A seismic risk index in building damage is defined using the total damaged floor area considering building size differences. The proposed seismic risk index was calculated for buildings in 29 administrative districts in 'A' city in Korea to validate the proposed assessment algorithm and risk index. In the validation procedure, sensitivity analysis was performed on the grid size, quantitative building damage measure, and seismic fragility function update.

• Journal of the Korean Geotechnical Society
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• v.32 no.11
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• pp.31-42
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• 2016

Usually the seismic stability analysis of slope uses the pseudostatic analysis considering the inertial force by the earthquake as a static load. Geostructures such as slope include the uncertainty of soil properties. Therefore, it is necessary to consider probabilistic method for stability analysis. In this study, the probabilistic stability analysis of slope considering the uncertainty of soil properties has been performed. The fragility curve that represents the probability of exceeding limit state of slope as a function of the ground motion has been established. The Monte Carlo Simulation (MCS) has been implemented to perform the probabilistic stability analysis of slope with pseudostatic analysis. A procedure to develop the fragility curve by the pseudostatic horizontal acceleration has been presented by calculating the probability of failure based on the Artificial Neural Network (ANN) based response surface technique that reduces the required time of MCS. The results showed that the proposed method can get the fragility curve that is similar to the direct MCS-based fragility curve, and can be efficiently used to reduce the analysis time.

• Journal of the Korean Geotechnical Society
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• v.33 no.7
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• pp.29-41
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• 2017

There are uncertainties about the seismic load caused by seismic waves, which cannot be predicted due to the characteristics of the earthquake occurrence. Therefore, it is necessary to consider these uncertainties by probabilistic analysis. In this paper, procedures to develop a fragility curve that is a representative method to evaluate the safety of a structure by stochastic analysis were proposed for cut slopes. Fragility curve that considers uncertainties of soil shear strength parameters was prepared by Monte Carlo Simulation using pseudo static analysis. The fragility curve considering the uncertainty of the input ground motion was developed by performing time-history seismic analysis using selected 30 real ground input motions and the Newmark type displacement evaluation analysis. Fragility curves are represented as the cumulative probability distribution function with lognormal distribution by using the maximum likelihood estimation method.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.203-210
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• 2004

The fragility curves of seismic retrofitted bridges by steel jacketing at bridge columns and restrainers at expansion joints after the 1994 Northridge earthquake are developed. Fragility curves are represented by lognormal distribution functions with two parameters (median and log-standard deviation) and developed as a function of peak ground acceleration(PGA). Two parameters in the lognormal distribution are estimated by the maximum likelihood method. The sixty ground acceleration time histories for Los Angeles area developed for FEMA SAC project are used for the dynamic analysis of bridges. The comparison of fragility curves of the bridges before and after column retrofit demonstrates that the improvement of the bridges with steel jacketing on the seismic performance is excellent for the damage states defined in this study. The comparison of fragility curves of the bridges before and after the installation of restrainers at expansion joints also shows the improvement in the seismic performance of restrained bridges for the severe damage state.

• Structural Engineering and Mechanics
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• v.76 no.6
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• pp.751-763
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• 2020

Available records of recent earthquakes show that near-field earthquakes have different characteristics than far-field earthquakes. In general, most of these unique characteristics of near-fault records can be attributed to their forward directivity. This phenomenon causes the records of ground motion normal to the fault to entail pulses with long periods in the velocity time history. The energy of the earthquake is almost accumulated in these pulses causing large displacements and, accordingly, severe damages in the building. Damage to structures caused by past earthquakes raises the need to assess the chance of future earthquake damage. There are a variety of methods to evaluate building seismic vulnerabilities with different computational cost and accuracy. In the meantime, fragility curves, which defines the possibility of structural damage as a function of ground motion characteristics and design parameters, are more common. These curves express the percentage of probability that the structural response will exceed the allowable performance limit at different seismic intensities. This study aims to obtain the fragility curve for low- and mid-rise structures of reinforced concrete moment frames by incremental dynamic analysis (IDA). These frames were exposed to an ensemble of 18 ground motions (nine records near-faults and nine records far-faults). Finally, after the analysis, their fragility curves are obtained using the limit states provided by HAZUS-MH 2.1. The result shows the near-fault earthquakes can drastically influence the fragility curves of the 6-story building while it has a minimal impact on those of the 3-story building.

• Journal of Ocean Engineering and Technology
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• v.24 no.5
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• pp.48-54
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• 2010

The analysis of the seismic risk of an offshore structure with a control device is presented. First, a probability density function was developed to represent seismic hazard, and seismic fragility under artificial earthquake conditions was determined. Fragility curves for an offshore structure with both passive and active control devices were determined. Displacement criteria were set to evaluate the performance of the structure. Based on numerical analysis, the seismic risk to the structure was considerably reduced when the structure had a seismic control device. The seismic risk to the actively controlled structure was decreased by 80% compared to the uncontrolled case. Reasonable performance evaluations of offshore structure with control devices can be conducted through risk analysis.

• Earthquakes and Structures
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• v.10 no.5
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• pp.1181-1212
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• 2016

Fragility and loss functions are developed to predict damage and economic losses due to earthquake loading in Reinforced Concrete (RC) structural components with smooth rebars. The attention is focused on external/internal beam-column joints and ductile/brittle weak columns, designed for gravity loads only, using low-strength concrete and plain steel reinforcing bars. First, a number of damage states are proposed and linked deterministically with commonly employed methods of repair and related activities. Results from previous experimental studies are used to develop empirical relationships between damage states and engineering demand parameters, such as interstory and column drift ratios. Probability distributions are fit to the empirical data and the associated statistical parameters are evaluated using statistical methods. Repair costs for damaged RC components are then estimated based on detailed quantity survey of a number of pre-70 RC buildings, using Italian costing manuals. Finally, loss functions are derived to predict the level of monetary losses to individual RC components as a function of the experienced response demand.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.8
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• pp.1491-1497
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• 2007

This paper considers robust and non-fragile guaranteed cost controller design method for descriptor systems with parameter uncertainties and time delay, and static state feedback controller with gain variations. The existence condition of controller, the design method of controller, the upper bound to minimize guaranteed cost function, and the measure of non-fragility in controller are proposed using linear matrix inequality (LMI) technique, which can be solved efficiently by convex optimization. Therefore, the presented robust and non-fragile guaranteed cost controller guarantees the asymptotic stability and non-fragility of the closed loop systems in spite of parameter uncertainties, time delay, and controller fragility.