• Structural Engineering and Mechanics
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• 제59권5호
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• pp.853-866
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• 2016

This paper examines a methodology for computing the probability of structural failure of reinforced concrete beams subjected to fire. The significant load variables considered are dead load, sustained live load and fire temperature. Resistance is expressed in terms of moment capacity with random variables taken as yield strength of steel, concrete class (or grade of concrete), beam width and depth. The flexural capacity is determined based on the design equations recommended in Indian standard IS456:2000. Simplified method named $500^{\circ}C$ isotherm method detailed in Eurocode 2 is incorporated for fire design. A transient thermal analysis is conducted using finite element software ANSYS$^{(R)}$ Release15. Reliability is evaluated from the initial state to 4h of fire exposure based on the first order reliability method (FORM). A procedure is coded in MATLAB for finding the reliability index. This procedure is validated with available literature. The effect of various parameters like effective cover, yield strength of steel, grade of concrete, distribution of reinforcement bars and aggregate type on reliability indices are studied. Parameters like effective cover of concrete, yield strength of steel has a significant effect on reliability of beams. Different failure modes like limit state of flexure and limit state of shear are checked.

• 한국지반환경공학회 논문집
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• 제4권2호
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• pp.77-91
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• 2003

연속체 해석을 위한 암반거동 모델로서 널리 이용되고 있는 Hoek-Brown 파괴기준은 1980년도에 발표된 이후 수차례의 수정 보완을 거쳐 1994년에 발표된 Generalized Hoek-Brown 파괴기준식을 토대로 현재 암반을 대상으로 한 지반구조물 해석에 많이 적용되고 있다. 그러나 지반구조물 수치해석시 Hoek-Brown 파괴기준의 적용은 일반적으로 등가의 Mohr-Coulomb 전단강도정수를 산정하여 간접적으로 이용하게 되는데, 이때 등가의 암반 전단강도정수를 암반내 주응력 분포와 상관없이 일정 상수로 적용함으로서 Hoek-Brown 파괴기준의 비선형성을 고려하지 못하는 단점이 있다. 따라서 본 연구에서는 암반사면의 안정성 평가를 위한 연속체 해석시 Hoek-Brown 파괴기준의 비선형성을 고려할 수 있는 해석기법을 검토하고, 수치해석기법에 의한 사면안정검토에 주로 이용되고 있는 강도감소법을 이용하여 암반사면의 안정성을 정량적으로 평가하고자 하였다. 특히 최근에 발표된 수정 Hoek-Brown 파괴기준을 토대로 수정된 등가 Mohr-Coulomb 강도정수 산정법과 사면굴착시 발파 및 응력이완에 의한 암반 교란/손상을 고려한 암반교란상수(Disturbance Factor) D을 이용하여 안정해석을 수행하였다.

• Composites Research
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• 제23권2호
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• pp.40-47
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• 2010

본 논문에서는 복합 반응면 기법을 제안하고 성능을 고찰하였다. 복합 반응면 기법은 MPP의 좌표를 기준으로 하여 근사모델을 반복 계산하는 기법이다. 성능을 검증하기 위해 비선형 함수와 복합재 적층판에 대하여 신뢰성 해석 기법을 적용하여 파괴확률, MPP(Most Probable failure Point), 신뢰도 지수를 계산하고 일반적인 반응면 기법의 결과와 비교하였다. 파괴확률은 비선형 한계상태식을 가정하고 임의의 파괴 기준을 정의하여 계산하였다. 제안한 복합 반응면 기법을 이용하여 파괴확률을 계산한 결과 일반적인 반응면 기법보다 향상된 성능을 나타내었다.

• 대한전기학회논문지:전력기술부문A
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• 제54권10호
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• pp.480-486
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• 2005

This paper proposes a method to consider an aging failure probability and survival probability of power system components, though only aging failure probability has been considered in existing mean life calculation. The estimates of the mean and its standard deviation is calculated by using Weibull distribution, and each estimated parameters is obtained from Data Analytic Method (Type H Censoring). The parameter estimation using Data Analytic Method is simpler and faster than the traditional calculation method using gradient descent algorithm. This paper shows calculation procedure of the mean life and its standard deviation by the proposed method and illustrates that the estimated results are close enough to real historical data of combustion turbine generating units in Korean systems. Also, this paper shows the calculation procedures of a probabilistic failure prediction through a stochastic data analysis. Consequently, the proposed methods would be likely to permit that the new deregulated environment forces utilities to reduce overall costs while maintaining an are-related reliability index.

• 한국해안·해양공학회논문집
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• 제21권5호
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• pp.405-409
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• 2009

중요도추출법을 이용한 항만구조물의 신뢰성해석방법을 제시하였다. 몬테카를로모사법(Monte Carlo Simulation)을 이용하여 신뢰성해석을 수행할 때 전도파괴확률과 같이 매우 낮은 파괴확률을 가진 경우는 해석시간이 과다하게 소요되는 문제점이 있다. 항만구조물 신뢰성해석 시 나타나는 이러한 문제를 극복하기 위해 파괴면주위의 추출점을 이용하여 해석시간을 단축시킬 수 있는 중요도추출법을 적용하였다. 중요도추출법을 항만구조물에 적용한 경우 파괴확률이 매우 낮은 파괴모드에 대한 신뢰성해석을 효율적으로 수행할 수 있음을 보였다. 수치해석에서 케이슨 안벽의 신뢰성해석을 수행하였으며 파괴확률의 낮고 높음에 따른 중요도추출법의 효용성을 검증하였다.

• 전기학회논문지
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• 제66권3호
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• pp.500-506
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• 2017

In 2014, ISO 55000s has been enacted and the power plant asset management is becoming a hot issue for all over the world. The asset management system is being developed as a combination of CBM(Condition Based Maintenance) and RCM(Reliability Centered Maintenance). Therefore, the research on the calculation of the failure rate which is the most basic index of RCM is actively carried out. The failure rate calculation has been going on for a long time, and the most widely used probability distribution is the Weibull distribution. In the Weibull distribution, the failure rate function is determined in three types according to the value of the shape parameter. However, the Weibull distribution has a limitation that it is difficult to apply it when the trend of failure rate changes-such as bathtub curves. In this paper, the failure rate is calculated using the mixture Weibull distribution which can appropriately express the change of the shape of the failure rate. Based on these results, we propose the necessity and validity of applying mixture Weibull distribution.

• Composites Research
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• 제15권4호
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• pp.9-16
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• 2002

복합재료가 항공기 구조물 및 기계 부품등에 폭 넓게 적용됨에 따라, 복합재료 구조물에서 가장 취약한 복합재료 체결부의 설계는 매우 중요한 연구분야로 대두되고 있다. 본 논문에서는 동일 적층순서를 가지는 복합재료 기계적 체결부의 강도를 예측하기 위하여 파괴면적지수법을 제안하고 복합재료 체결부의 강도를 예측하였다. 제안된 파괴면적지수법에 의하여 기계적 체결구조를 갖는 복합재료의 체결부의 강도를 예측한 결과, 6.03%내에서 체결부의 강도를 예측할 수 있었다.

• Industrial Engineering and Management Systems
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• 제4권2호
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• pp.192-197
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• 2005

Among many amplitude parameters, Kurtosis (4-th normalized moment of probability density function) is recognized to be the sensitive good parameter for machine diagnosis. Kurtosis has a value of 3.0 under normal condition and the value generally goes up as the deterioration proceeds. In this paper, simplified calculation method of kurtosis is introduced for the analysis of impact vibration with one sided affiliated impact vibration which occurs towards the progress of time. That phenomenon is often watched in the failure of such as bearings’ outer race. One sided affiliated impact vibration is approximated by one sided triangle towards the progress of time and simplified calculation method is introduced. Varying the shape of one sided triangle, various models are examined and it is proved that new index is a sensitive good index for machine failure diagnosis. Utilizing this method, the behavior of kurtosis is forecasted and analyzed while watching machine condition and correct diagnosis is executed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 A
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• pp.29-31
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• 2006

The most crucial requirement of a power system is o supply quality electric energy to customers without interrution. This problem is directly related to reliability of power system. Reliability assessment of power system has been an important topic for the past several decades. This paper deals with reliability assessment of a 154kV power substation n KEPCO. In his paper, exponential distribution is used to calculate reliablity index. The failure rate data that are utilited for reliablity index based on the realistic system. Also, FTA(Fault Tree Analysis) is used to compute substation reliablity

• 대한전기학회논문지:전력기술부문A
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• 제48권10호
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• pp.1198-1205
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• 1999

This study is focused on the reliability evaluation for distribution system based on deterministic evaluation technique. Average failure rates, average outage time, and average annual outage time of electrical parts and load points are calculated through network reduction method and failure mode & effective analysis method. And reliability indices of distribution system are calculated. Finally, by employing analytic hierarchy process method, unique index which evaluates and improves the distribution system is calculated. As a result, finding weak points and expansion schedule of the system is possible. The usefulness of this method is verified by applying it to the Inchon International Airport.