• Journal of computational fluids engineering
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• v.17 no.2
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• pp.28-34
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• 2012

In this study, the reliability-based design optimization of the airfoil was performed. PARSEC function was used to consider the uncertainty of the aerodynamic shape for the reliability-based shape optimization of airfoils. Among various reliability analysis methods, the moment method was used to compute the probability of failure of the aerodynamic performance. The accuracy of the reliability analysis was compared with other methods and it was found that the moment method predicts the probability of failure accurately. Deterministic and reliability-based optimizations were performed for the shape of the airfoil and it was demonstrated that reliability-based optimum assures the aerodynamic performances under uncertainties of the shape of the airfoil.

• Computational Structural Engineering
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• v.5 no.4
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• pp.113-124
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• 1992

This study proposes a Load Factors-based Analysis Model of Optimum Reliability for the High way bridge, which is most common type of structural design, and also proposes the theoretical bases of optimum nominal safety factors as well as optimum load and resistance factors based on the expected total cost minimization. Major 2nd moment reliability analysis and design theories including both MFOSM(Mean First Order 2nd Moment) Methods and AFOSM(Advanced First Order 2nd Moment) Methods are summarized and compared, and it has been found that Lind-Hasofer's approximate and an approximate Log-normal type reliability for mula are well suited for the proposed optimum reliability study.

• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.103-110
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• 2009

Concrete carbonation is a cause of problems in concrete structures, so it needs to be estimated. And concrete cover is designed to protect structures from this damaging. Usually the cover thickness is considered based on the limit states design codes in which the important target is the reliability safety index. However, it is not clear that whether the safety index determined is optimal or not with respect to the cost. The codes are mainly proceeded quantitatively (i.e. making a safe structure) while the economic aspects are only considered qualitatively. So the reliability-based design considering life cycle cost (LCC) is called for, and here the focus is on the advanced analysis solution to optimize the reliability safety regarding LCC.

• Structural Engineering and Mechanics
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• v.45 no.2
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• pp.201-209
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• 2013

A new dynamic reliability analysis of structure under repeated random loads is proposed in this paper. The proposed method is developed based on the idea that the probability density of several times random loads can be derived from the probability density of single-time random load. The reliability prediction models of structure based on time responses under several times random loads with and without strength degradation are obtained by using the stress-strength interference theory and probability density evolution method. The resulting differential equations in the prediction models can be solved by using the forward finite difference method. Then, the probability density functions of strength redundancy of the structures can be obtained. Finally, the structural dynamic reliability can be calculated using integral method. The efficiency of the proposed method is demonstrated numerically through a speed reducer. The results have shown that the proposed method is practicable, feasible and gives reasonably accurate prediction.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.102-110
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• 2010

The reliability evaluation may be a efficient method for estimating of the quantitative structural safety considering the effect of uncertainties included in high-speed railway bridges. The expected life-cycle cost(LCC) based upon the reliability evaluation will reasonably offer the safety level and design criteria of high-speed railway bridges. Therefore, this study determined the expected life-cycle cost and optimal design method of high-speed railway bridges on the basis of the result of the numerical analysis and reliability evaluation. For this, after creating various design method based upon the standard design of high-speed railway bridges, the numerical analysis is conducted on each of the alternative design methods. The reliability evaluation by the design strength limit state function is conducted considering the effect of external uncertainties on the basis of the numerical analysis result. The expected life-cycle cost of high-speed railway bridges is calculated on the basis of the reliability evaluation result by each of the alternative design methods. Also, the optimal design method is determined using the calculated expected life-cycle cost. In addition, The result of reliability evaluation and expected life-cycle cost of optimal design method are examined considering the effect of internal uncertainties. It is expected that the result of this study can be used as a basic information for the systematic safety evaluation and optimal structure design of high-speed railway bridges.

• Computers and Concrete
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• v.6 no.1
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• pp.59-78
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• 2009

Reliability analysis for a proposed limit state bridge design code is performed. In order to introduce reliability concept to design code, the proposed live load model is based on truck weight survey. Test data of domestic material strengths are collected to model statistical properties of member strengths. Sample RC and PSC girder sections are designed following the safety factor format of the proposed code and compared with the current design practice. Reliability indexes are calculated and examined for material and member resistance factor formats and sample calibrations of safety factors are presented. It is concluded that the proposed code provides reasonable level of reliability compared to the international design standards.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.2 no.3
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• pp.87-99
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• 1982

This study proposes a reliability based design criteria for the R.C. superstructures of highway bridges. Uncertainties associated with the resistance of T or rectangular sections are investigated, and a set of appropriate uncertainties associated with the bridge dead and traffic live loads are proposed by reflecting our level of practice. Major 2nd moment reliability analysis and design theories including both Cornell's MFOSM(Mean First Order 2nd Moment) Methods and Lind-Hasofer's AFOSM(Advanced First Order 2nd Moment) Methods are summarized and compared, and it has been found that Ellingwood's algorithm and an approximate log-normal type reliability formula are well suited for the proposed reliability study. A target reliability index (${\beta}_0=3.5$) is selected as an optimal value considering our practice based on the calibration with the current R.C. bridge design safety provisions. A set of load and resistance factors is derived by the proposed uncertainties and the methods corresponding to the target reliability. Furthermore, a set of nominal safety factors and allowable stresses are proposed for the current W.S.D. design provisions. It may be asserted that the proposed L.R.F.D. reliability based design criteria for the R.C. highway bridges may have to be incorporated into the current R.C. bridge design codes as a design provision corresponding to the U.S.D. provisions of the current R.C. design code.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.39 no.12
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• pp.1150-1159
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• 2011

Reliability is defined as a probability that a system will operate properly for a specified period of time under the design operating conditions without failure. Reliability-Redundancy Optimization Problem(RROP) involves selection of components with multiple choices, redundancy levels and redundancy strategy(Active or Standby) for maximizing system reliability with constraints such as cost, weight, etc. Based on the design configuration of Multi-Spectral Camera(MSC) system of KOMPSAT-2, the mathematical programming model for RROP is suggested in this study. Due to the nature of RROP, i.e. NP-hard problem, Parallel Particle Swarm Optimization(PPSO) algorithm is proposed to solve it. The result of the numerical experiment for RROP is presented as instance of recommended design configuration at some mission time.

• Journal of Korean Society for Quality Management
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• v.43 no.3
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• pp.373-382
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• 2015

Purpose: In this paper, we developed a reliability index (RI) to efficiently compare reliability of products based on the design, development and production information such as reliability tests, quality, product life-cycle management. RI also can be applied to reliability prediction of a novel product as well as comparison evaluation among existing products. Methods: For evaluating RI, we proposed evaluation process which is composed of five steps. Target modules are selected based on warranty data and correlation analysis. Scores of selected target modules are calculated by scoring function. Finally, weights of RI model are determined by optimization method. Results: This paper presented an empirical analysis based on failure data of mobile devices. In this case study, we demonstrated that there is a direct correlation between evaluated RI and field failure probability of each product. Conclusion: We proposed the index for comprehensive and effective assessment of product reliability level. From the procedure of this study, we expected to be applied for reliability estimation of novel products and deduction of field failure-related factors.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1992.10a
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• pp.79-89
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• 1992

This study is directed to propose a stability analysis and Design Criteria for Bridge Caisson foundations, with Could possibly replace the traditionals W.S.D. provisions of the Current Code, based on the FBOR(Load Factors based on optimum Reliability). The optimum reliability indices(Vertical bearing Capacity : $\beta$opt : 3.19, Lateral bearing Capacity : $\beta$opt= 3.15(ordinary), $\beta$opt : 2.93 (earthquake), Shearing resistance Capacity ; $\beta$opt : 2.87) are Selected as optimal Values Considering our practice base on the Calibration with the current Bridge Caisson foundation design Safety provisions, Load and resistance factors are measure by Using the proposed uncertainties and the Selected optimum reliability indices. furthermore, a set of nominal safety factors are proposed for the U.S.D. design provisions.