• KSCE Journal of Civil and Environmental Engineering Research
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• v.36 no.3
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• pp.451-461
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• 2016

The objective of this study is to illustrate the methods and procedures for estimating the failure probability of small fill dams subjected to earthquake events and to estimate the seismic failure probability of the Korean disaster risk fill dams where geotechnical information is not available. In this study, first of all, seismic failure probabilities of 7 disaster risk small fill dams, where geotechnical information is available, were evaluated using event tree analysis. Also, the methods and procedures for evaluating probabilities are illustrated. The relationship between dam height and freeboard for 84 disaster risk small dams, for which the safety diagnosis reports are available, was examined. This relationship was associated with the failure computation equation contained in the toolbox of US Army corps of engineers. From this association, the dam height-freeborard critical curve, which represents 'zero' failure probability, was derived. The seismic failure probability of the Korean disaster risk fill dams was estimated using the critical curve and the failure probabilities computed for 7 small dams.

• Journal of the Korean GEO-environmental Society
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• v.18 no.3
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• pp.31-38
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• 2017

The purpose of this study is to propose a chart that can easily estimate the seismic failure probability of small and medium sized earthfill dams with little geotechnical information. By considering the existing method and procedure for estimating the seismic failure probability of a dam, the zero seismic failure probability curve, on which the seismic probability is zero regardless of the geotechnical properties of the dam, was determined in the form of hyperbola in the dam height and freeboard ratio plane. It was confirmed that the dam height-freeboard ratio distribution pattern of the Korean small and medium sized dams was shaped like a hyperbola like the zero seismic failure probability curve. Therefore, a estimation chart was constructed in which a number of seismic failure probability contours are represented by a number of hyperbolas at regular intervals in the dam height-freeboard ratio plane. The proposed chart was applied to the calculation of the seismic failure probability of two small and midium sized dams with relatively well-managed geotechnical properties and the validity of the chart was confirmed by comparison with the results obtained by the existing procedures and methods. In the future, the proposed chart is expected to be useful in considering investment priorities for maintenance and reinforcement of small and medium sized dams in preparation for earthquakes.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.53-64
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• 2018

In this study, the evaluation to probability of failure for risk assessment of port structures on DCM reinforced soils, where stability and risk assessment are increasing in importance, was performed. As a random variables affecting the risk of DCM improved ground, the design strength, superposition (overlap) of construction, strength of the natural ground, internal friction angle and unit weight of the modified ground were selected and applied to the risk assessment. In addition, the failure probability for the entire system under ordinary conditions and under earthquake conditions were analyzed. As a result, it was found that the highest coefficient of variation in the random variable for the risk assessment of the DCM improved ground is the design strength, but this does not have a great influence on the safety factor, ie, the risk of the system. The main risk factor for the failure probability of the system for the DCM reinforced soils was evaluated as horizontal sliding in case of external stability and compression failure in case of internal stability both at ordinary condition and earthquake condition. In addition, the failure probability for ordinary horizontal sliding is higher than that for earthquake failure, and the failure probability for ordinary compression failure is lower than that for earthquake failure. The ordinary failure probability of the entire system is similar to the failure probability on earthquake condition, but in this case, the risk of earthquake is somewhat higher.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.1
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• pp.25-34
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• 2010

A method is presented for evaluating the seismic failure probability of bridge structures which show a nonlinear hysteretic dynamic behavior. Bridge structures are modeled as a bilinear dynamic system with a single degree of freedom. We regarded that the failure of bridges will occur when the displacement response of a deck level firstly crosses the predefined limit state during a duration of strong motion. For the estimation of the first-crossing probability of a nonlinear structural system excited by earthquake motion, we computed the average frequency of crossings of the limit state. We presented the non-Gaussian closure method for the approximation of the joint probability density function of response and its derivative, which is required for the estimation of the average frequency of crossings. The failure probabilities are estimated according to the various artificial earthquake acceleration sets representing specific seismic characteristics. For the verification of the accuracy and efficiency of presented method, we compared the estimated failure probabilities with the results evaluated from previous methods and the exact values estimated with the crude Monte-Carlo simulation method.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.2
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• pp.47-58
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• 2009

In this study, a seismic fragility analysis was performed for substation systems in Korea. To evaluate the seismic fragility function of the substation systems, a fragility analysis of the individual equipment and facilities of the substation systems was first performed, and then all systems were considered in the fragility analysis of the substation systems using a fault-tree method. For this research, the status of the substation systems in Korea was investigated for the classification of the substation systems. Following the classification of the substation systems, target equipment was selected based on previous damage records in earthquake hazards. The substation systems were classified as 765kV, 345kV, and 154kV systems. Transformer and bushing were chosen as target equipment. The failure modes and criteria for transformer and bushing were decided, and fragility analysis performed. Finally, the fragility functions of substation system were evaluated using the fault tree method according to damage status.

• Journal of Korean Tunnelling and Underground Space Association
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• v.22 no.3
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• pp.249-259
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• 2020

Design criteria for limit state design of underground structures have already been published overseas, and research has been conducted to revise the design method in Korea. In order to estimate the probability of failure under seismic load, the probability variable should be considered in the reliability analysis. In this study, the failure probability of the existing shield tunnel segment lining design was calculated by applying the coefficient of variation (COV) for the earth pressure and the seismic load effect in consideration of the statistical characteristics of the domestic ground properties. Based on the results of calculating the reliability index (β) from the calculated probability of failure and analyzing the reliability index according to the change in the load factor and the results of domestic and foreign research, the target reliability index (β_T) during earthquakes of shield tunnel segment lining is analyzed to be "2.3", it was proposed as the target reliability index for the design of the limit state under seismic load.

• Geotechnical Engineering
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• v.5 no.1
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• pp.27-34
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• 1989

This study presents a probabilistic analysis of the stability of homogeneous soil slopes during earthquakes. The stability of the slope is measured through its probability of failure rather than the customary factor of safety. The maximum horizontal ground acceleration is deterimined with Donovan and McGuire equation. The earthquake magnitude (m) is a random variable the Probability density function f(m) has been obtained with a use of Richter law. The potential failure surfaces are taken to be of an exponential shape (log-spiral) , Uncertainties of the shear strength parameters along potential failure surface are expressed by one-dimensional random field model. From a first order analysis the mean and variance of safety margin is osculated. The dependence on significant seismic parameters of the probability of failure of the slope is examined and the results are presented in a number of graphs and tables. On the base of the results obtained in this study, it is concluled that (1) the present model is useful in assessing the reliability of soil slopes under both static and seismic conditions: and (2) the probability of failure of a soil slope is greatly affected by the values of the seismic parameters that are associated with it.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.442-445
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• 2009

지진에 대한 건축물의 확률적 성능평가에 대해서는 지진하중에 대한 건축물의 손상확률 또는 파괴확률을 나타내는 지진취약도 함수를 작성하여 대상 건축물에 대한 지진위험도를 평가하는 방법을 이용하고 있으며 이에 대한 많은 연구가 이루어지고 있다. 본 연구에서는 지진하중과 구조물 재료특성의 불확실성을 고려하고 대상 건축물의 지진취약도 해석을 통하여 비내력벽의 유무에 따른 건축물의 지진거동 및 내진성능을 평가하였다. 비내력벽을 보편화된 모형화 방법인 등가의 대각 압축 스트럿으로 고려하여 비내력벽의 유무에 따른 저층 철근콘크리트 건축물을 모형화하였으며 지진하중의 강도는 유효최대지반가속도를 이용하여 각 건축물에 대하여 지진취약도를 작성하였다. 취약도해석 결과로 연약층을 가지고 있는 건축물의 경우는 손상확률이 골조만 있는 경우보다 크며 동일한 해석모델의 경우에도 해석방법에 따라서 취약도 곡선의 형태가 다름을 알 수 있었다.

• Journal of the Society of Disaster Information
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• v.15 no.4
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• pp.626-633
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• 2019

Purpose: The primery objecting of this paper is to explore the seismics fragility of curved bridge based on the change of girder section. Method: The cross section of the bridge structure was constructed with I, T, and Box shapes and then, in order to perform the seismic fragility 24 seismic ground motions were used, including Gyeongju Pohang Earthquake. Result: Fist, T-Shape of the bridge strucrue was much fragility in terms of the stress on girder section, in comparison to the other shapes. The seismic fragilies of the structures with respect to displacement(drift ratio), however, were shown simialr. Conclusion: In other to wvaluation the seismic fragility of curved structure using different girder shapes, analytical models of the structure were constructed and then, the probability failure of box-shape girder was shown lower probability. In further, Parametric studies of curved structures must be conducted.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.2
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• pp.1-13
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• 2010

This paper proposes an optimal design method for the nonlinear seismic isolated bridge. The probabilities of failure at the pier and the seismic isolator are considered as objective functions for optimal design, and a multi-objective optimization technique is employed to efficiently explore a set of multiple solutions optimizing mutually-conflicting objective functions at the same time. In addition, a stochastic linearization method is incorporated into the multi-objective optimization framework in order to effectively estimate the stochastic responses of the bridge without performing numerous nonlinear time history analyses during the optimization process. As a numerical example to demonstrate the efficiency of the proposed method, the Nam-Han river bridge is taken into account, and the proposed method and the existing life-cycle-cost based design method are both applied for the purpose of comparing their seismic performances. The comparative results demonstrate that the proposed method not only shows better seismic performance but also is more economical than the existing cost-based design method. The proposed method is also proven to guarantee improved performance under variations in seismic intensity, in bandwidth and in the predominant frequency of the seismic event.