• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.324-337
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• 2010

For the development of load and resistance factor design, reliability analysis is required to calibrate resistance factors in the framework of reliability theory. The distribution of measured-to-predicted pile resistance ratio was constructed based on only the results of load tests conducted to failure for the assessment of uncertainty regarding pile resistance and used in the conventional reliability analysis. In other words, successful pile load test (piles resisted twice their design loads without failure) results were discarded, and therefore, were not reflected in the reliability analysis. In this paper, a new systematic method based on Bayesian theory is used to update reliability index of driven steel pile piles by adding more pile load test results, even not conducted to failure, into the prior distribution of pile resistance ratio. Fifty seven static pile load tests performed to failure in Korea were compiled for the construction of prior distribution of pile resistance ratio. Reliability analyses were performed using the updated distribution of pile resistance ratio and the total load distribution using First-order Reliability Method (FORM). The challenge of this study is that the distribution updates of pile resistance ratio are possible using the load test results even not conducted to failure, and that Bayesian update are most effective when limited data are available for reliability analysis or resistance factors calibration.

• 한국산학기술학회논문지
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• 제21권11호
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• pp.884-891
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• 2020

교량은 현대 사회에서 중요한 사회기반시설물 중에 하나로 교량의 붕괴는 막대한 인명 피해와 경제적 손실을 일으킬 수 있다. 따라서 교량의 구조적 안전성을 평가하는 것은 매우 중요하며, 이를 위해 교량을 둘러싼 여러 종류의 불확실성 요인들을 고려하는 구조신뢰성 해석이 흔히 사용된다. 본 연구에서는 다양한 하중 조건에서 교량의 안전성을 평가하기 위한 새로운 구조신뢰성 해석 플랫폼을 제안한다. 제안 플랫폼 FERUM-MIDAS는 신뢰성 해석 소프트웨어인 Finite Element Reliability Using MATLAB(FERUM)과 교량 설계/해석에 특화된 상용 소프트웨어인 MIDAS/CIVIL을 연결하여, 자동적인 입출력 데이터 교환을 통해서 구조신뢰성 해석을 수행한다. 나아가 MIDAS/CIVIL의 그래픽 사용자 인터페이스로만 소프트웨어 구동이 가능한 한계점을 극복하기 위하여 FERUM에 별도의 그래픽 사용자 인터페이스 제어 모듈을 추가하였다. 본 연구에서는 제안 플랫폼을 간단한 프레임 예제에 적용하여 대표적인 신뢰성 해석 방법인 FORM(First-Order Reliability Method)과 MCS(Monte Carlo simulation)의 해석 결과를 비교·분석하였으며, 계산된 파괴확률 차이가 5% 미만인 것을 확인하여 제안 플랫폼의 검증을 완료하였다. 이와 더불어 개발된 플랫폼을 활용하여 KL-510 활하중 모델을 고려한 프리스트레스트 콘크리트(pre-stressed concrete, PSC)교의 파괴확률과 신뢰도 지수를 도출하고, 그 결과를 분석하여 교량의 구조적 안전성을 평가하였다. 본 연구에서 제안한 새로운 구조신뢰성 해석 플랫폼을 통해 교량의 효과적인 신뢰도 기반 안전성 평가가 가능할 것으로 기대된다.

• Steel and Composite Structures
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• 제42권1호
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• pp.59-74
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• 2022

This study introduces a general reliability-based, performance-based design framework to design frames regarding their uncertainties and user-defined design goals. The Iterative-R method extracted from the main framework can designate a proper R (i.e., response modification factor) satisfying the design goal regarding target reliability index and pre-defined probability of collapse. The proposed methodology is based on FEMA P-695 and can be used for all systems that FEMA P-695 applies. To exemplify the method, multiple three-dimensional, four-story steel special moment-resisting frames are considered. Closed-form relationships are fitted between frames' responses and the modeling parameters. Those fits are used to construct limit state functions to apply reliability analysis methods for design safety assessment and the selection of proper R. The frameworks' unique feature is to consider arbitrarily defined probability density functions of frames' modeling parameters with an insignificant analysis burden. This characteristic enables the alteration in those parameters' distributions to meet the design goal. Furthermore, with sensitivity analysis, the most impactful parameters are identifiable for possible improvements to meet the design goal. In the studied examples, it is revealed that a proper R for frames with different levels of uncertainties could be significantly different from suggested values in design codes, alarming the importance of considering the stochastic behavior of elements' nonlinear behavior.

• 한국신뢰성학회지:신뢰성응용연구
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• 제5권3호
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• pp.327-342
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• 2005

전자 패키지가 열을 받을 때 회로기판과 칩의 열팽창계수 차이에 의해 발생되는 응력은 솔더 조인트의 파손에 영향을 미친다. 본 연구에서는 이 영향을 정량적으로 규명하기 위하여 열충격시험기를 이용해 얻어진 솔더 조인트의 전기저항 변화와 수명과의 상관관계를 규명하였고, BGA솔더 조인트의 수명을 정량적으로 도출하였다. 또한 Sn-3.5Ag-0.5Cu 무연 솔더와 63Sn-37Pb 유연 솔더를 위의 실험에 동시에 적용시켜 건전성을 FORM(first-order reliability method)과 Weibull Function Model을 이용해 비교하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1992년도 봄 학술발표회 논문집
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• pp.51-57
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• 1992

The primary objective of this study is the development of second moment methods for the efficient reliability evaluations of structural systems. Two methods are presented. One is the improved first order reliability method (IFORM), and the other is the modified probabilistic network evaluation technique (MPNET). For the purpose of verifying the proposed methods, example analyses are carried out on several cases with two failure modes, a plane frame structure involving three failure modes and simplified parallel member models for fatigue reliability evaluations of offshore structures. Numerical results indicate that the effectiveness of the proposed methods over the conventional ones (i.e., the FORM and the PNET) increases very significantly as the number of failure modes of the system increases.

• 한국신뢰성학회:학술대회논문집
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• 한국신뢰성학회 2005년도 학술발표대회 논문집
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• pp.287-294
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• 2005

전자 패키지가 열을 받을 때 회로기판과 칩의 열팽창계수 차이에 의해 발생되는 응력은 솔더 조인트의 파손에 영향을 미친다. 본 연구에서는 이 영향을 정량적으로 규명하기 위하여 열충격시험기를 이용해 얻어진 솔더조인트의 전기저항 변화와 수명과의 상관관계를 규명하였고, BGA 솔더조인트의 수명을 정량적으로 도출하였다. 또한 Sn-3.5Ag-0.5Cu 무연솔더와 63Sn-37Pb 유연솔더를 위의 실험에 동시에 적용시켜 건전성을 FORM(first-order reliability method)과 Weibull Function Model을 이용해 비교하였다.

• 대한기계학회논문집A
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• 제33권12호
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• pp.1464-1470
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• 2009

RBDO approach based on a sampling method with the Kriging metamodel and Constraint Boundary Sampling (CBS), which is sequential sampling method to generate metamodels is proposed. The major advantage of the proposed RBDO approach is that it does not require Most Probable failure Point (MPP) which is essential for First-Order Reliability Method (FORM)-based RBDO approach. The Monte Carlo Sampling (MCS), most well-known method of the sampling methods for the reliability analysis is used to assess the reliability of constraints. In addition, a Cumulative Distribution Function (CDF) of the constraints is approximated using Moving Least Square (MLS) method from empirical distribution function. It is possible to acquire a probability of failure and its analytic sensitivities by using an approximate function of the CDF for the constraints. Moreover, a concept of inactive design is adapted to improve a numerical efficiency of the proposed approach. Computational accuracy and efficiency of the proposed RBDO approach are demonstrated by numerical and engineering problems.

• Structural Engineering and Mechanics
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• 제36권1호
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• pp.19-36
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• 2010

The load and resistance factors are generally obtained using the First Order Reliability Method (FORM), in which the design point should be determined and derivative-based iterations have to be used. In this paper, a simple method for estimating the load and resistance factors using the first four moments of the basic random variables is proposed and a simple formula for the target mean resistance is also proposed to avoid iteration computation. Unlike the currently used method, the load and resistance factors can be determined using the proposed method even when the probability density functions (PDFs) of the basic random variables are not available. Moreover, the proposed method does not need either the iterative computation of derivatives or any design points. Thus, the present method provides a more convenient and effective way to estimate the load and resistance factors in practical engineering. Numerical examples are presented to demonstrate the advantages of the proposed fourth moment method for determining the load and resistance factors.

• Geomechanics and Engineering
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• 제29권6호
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• pp.599-614
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• 2022

In this study, the reliability analysis of internal and external stabilities of Reinforced Soil Walls (RSWs) under static and seismic loads are investigated so that it can help the geotechnical engineers to perform the design more realistically. The effect of various variables such as angle of internal soil friction, soil specific gravity, tensile strength of the reinforcements, base friction, surcharge load and finally horizontal earthquake acceleration are examined assuming the variables uncertainties. Also, the correlation coefficient impact between variables, sensitivity analysis, mean change, coefficient of variation and type of probability distribution function were evaluated. In this research, external stability (sliding, overturning and bearing capacity) and internal stability (tensile rupture and pull out) in both static and seismic conditions were investigated. Results of this study indicated sliding as the predominant failure mode in the external stability and reinforcing rupture in the internal stability. First-Order Reliability Method (FORM) are applied to estimate the reliability index (or failure probability) and results are validated using the Monte Carlo Simulation (MCS) method. The results showed among all variables, the internal friction angle and horizontal earthquake acceleration have dominant impact on the both reinforced soil wall internal and external stabilities limit states. Also, the type of probability distribution function affects the reliability index significantly and coefficient of variation of internal friction angle has the greatest influence in the static and seismic limits states compared to the other variables.

• 대한토목학회논문집
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• 제28권1C호
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• pp.19-29
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• 2008

국내 기초구조물에 대한 하중저항계수설계법 개발의 일환으로 항타강관말뚝에 대한 신뢰성 수준을 평가하고 목표 신뢰도지수를 결정하였다. 국내 정재하시험 및 지반조사 자료를 수집하여 말뚝의 대표 측정 극한지지력을 결정하였고, 정역학적 지지력공식과 Meyerhof 경험식을 이용하여 설계 극한지지력을 산정하였다. 이들 자료의 비교 분석을 통해 저항편향계수를 산정하였다. 저항편향계수의 통계 특성을 이용하여 일차신뢰도법 및 몬테카를로 시뮬레이션에 의한 신뢰성 분석을 실시하였다. 정역학적 지지력공식은 자료의 변동성이 낮았고 Meyerhof 경험식은 내재적 보수성이 크게 나타났다. 안전율 3.0~5.0에 대한 신뢰도지수 분석 결과 정역학적 지지력공식은 1.50~2.89, Meyerhof 경험식은 1.61~2.72로 평가되었다. 신뢰성 분석 결과를 바탕으로 목표 신뢰도지수는 무리말뚝으로 시공되는 경우 2.0, 2.33을, 무리말뚝으로 시공되지 않는 경우 2.5의 값을 결정하였다.