• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.43-52
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• 2003

The present study is to investigate the ultimate behavior and limit state design of 2-I) R/C structures, with the changing of crack direction, and the yielding of the reinforcing steel bars, and Is to introduce an algorithm for the limit state design and analysis of 2-D R/C structures, directly from the finite element model. For the design of reinforcement in concrete the limit state design equation is incorporated into finite element algorithm to be based on the pointwise elemental ultimate behavior. It is also introduced a simplified nonlinear analysis algorithm for stress-strain relationship of R/C plane stress problem considering the cracking and its rotation in concrete and the yielding of the reinforcing steel bar. The algorithm is incorporated into the nonlinear finite element analysis. The analysis model is compared with the experimental model of R/C shear wall. In a simple design example for a shear wall, the required reinforcement ratios in each finite element is obtained from the limit state design equations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.12
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• pp.1186-1192
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• 2008

The reliability of gas turbine engine blades was studied. Yield strength, Young’s modulus, engine speed and gas temperature were considered as statistically independent random variables. The failure probability was calculated using five different methods. Advanced Mean Value Method was the most efficient without significant loss in accuracy. When random variables were assumed to have normal, lognormal and Weibull distributions with the same means and standard deviations, the CDF of limit state equation did not change significantly with the distribution functions of random variables. The normalized sensitivity of failure probability with respect to standard deviations of random variables was the largest with gas temperature. The effect of means and standard deviations of random variables was studied. The increase in the mean of gas temperature and the standard deviation of engine speed increased the failure probability the most significantly.

• Journal of the Korean Chemical Society
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• v.40 no.6
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• pp.409-414
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• 1996

The limit of applicability of Navier-Stokes equation to stationary plane shock-waves is examined by using the principle of minimum entropy production of linear irreversible thermodynamics. In order to obtain analytic results, the equation is linearized near the equilibrium of downstream. Results show that the solution of Navier-Stokes equation which fits the boundary condition of far downstream flow is consistent with the thermodynamic requirement within the first order when the solution is expanded around the M=1, where M is the Mach number of upstream speed.

• The Korean Journal of Applied Statistics
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• v.23 no.4
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• pp.747-757
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• 2010

This paper studies the Markov modeling of multiclass loss systems supporting several kinds of customers. The concept of unit for loss systems is introduced and the method of equal probability allocation among units is especially considered. Equilibrium equations and limiting distribution of the loss systems are studied and loss probabilities are computed. We analyze an example of a simple system to gain an insight about general systems.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.817-820
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• 2008

이 논문은 초고강도 섬유보강 I형 보의 거동을 Diana를 사용하여 3차원 유한요소해석을 수행하였다. 보통 또는 고강도 콘크리트의 구성방정식과 달리 초고강도 섬유보강 콘크리트의 재료적 특성 즉, 인장 변형률 강화를 고려한 탄-소성 파괴 역학적 모델을 제안하여 해석에 반영하였다. 인장영역에서는 인장 변형률 강화를 고려한 다차원 고정 균열 규준을 사용하였고, 압축영역에서는 associated flow rule을 고려한 Drucker-Prager Criterion을 채택하였다. UHPFRC(Ultra-High Performance Fiber Reinforced Concrete) I형 보의 하중변형관계, 최초 균열, 최초 대각 균열, 극한상태 등의 결과를 실험결과와 비교하여 해석법의 유용성을 입증하였다.

• Korean Chemical Engineering Research
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• v.48 no.2
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• pp.224-231
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• 2010

In GvdW EOS, a recently presented paper, shows that the characteristic status for spherical non-linear particle, of which the mutual behavior is known to be vdWf(van der Waals force) only, could be described well enough in the critical region. However, in current papers, analysis has not been done on GvdW about whether it is accurate or not, even for the particles in the linear form or those with the additional mutual behavior such as static-electricity, so there's some argument about the wide use of that. Therefore, in this paper, for the simulation in the critical region of Normal-alkane group(R=methane, ethane, propane, butane) which are the particles that has a linear charateristic and Normal-amine group($RNH_2$, R=methyl-, ethyl-, propyl-amine) where static-electricity is extremely shown, GvdW parameter values about these particles are defined, and based on this simulation, we compared results to the current EOS presented recently, and analyzed them. Through the simulation, it was shown that in case of Normal-alkane group and Normal-amine group molecules, GvdW presents an accurate critical region characteristic which is far more close to the measurement compared to current EOSs. Especially for butane with big amount in molecules, we found out that only GvdW EOS can reach close enough to the critical point.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.647-657
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• 2006

Probabilistic Risk Assessment considering statistically random variables is performed for the preliminary design of a Cable Stayed Bridge, which is Prestressed Concrete Bridge consisted of cable and plate girders, based on the method of Working Stress Design and Strength Design. Component reliabilities of cables and girders have been evaluated using the response surface of the design variables at the selected critical sections based on the maximum shear, positive and negative moment locations. Response Surface Method (RSM) is successfully applied for reliability analyses for this relatively small probability of failure of the complex structure, which is hard to obtain through Monte-Carlo Simulations. or through First Order Second Moment Method that can not easily calculate the derivative terms of implicit limit state functions. For the analysis of system reliability, parallel resistance system consisting of cables and plate girder is changed into series connection system and the result of system reliability of total structure is presented. As a system reliability, the upper and lower probabilities of failure for the structural system have been evaluated and compared with the suggested prediction method for the combination of failure modes. The suggested prediction method for the combination of failure modes reveals the unexpected combinations of element failures in significantly reduced time and efforts compared with the previous permutation method or system reliability analysis method, which calculates upper and lower bound failure probabilities.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.4A
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• pp.383-389
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• 2010

The concrete structural design provisions in Korea are based on ultimate strength design. Up to service load stage, it is assumed a linear stress-strain relation, but there is no stress-strain relationship for a concrete material from service load stage to limat state. According to the current provisions, an independent method is provided for the each calculation of deflection and crack width. In EC2 provisions based on limit state design, however, a stress-strain relationship of concrete is provided. Thereby, it is able to calculate a strength as well as a deflection directly from concrete stress-strain relationship. In this paper the moment-curvature relationship is directly calculated from a material law using equilibrium and compatibility conditions. Then strength and deflection are formulated. These results are compared with the values from the current provisions in Korea. From the results, the deflection based on a moment-curvature relationship is well agreed with experimental results and it is appeared that the deflection after the yielding of steel is also possible.

• Computational Structural Engineering
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• v.4 no.2
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• pp.111-117
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• 1991

The analysis method calculating the mean and standard deviation for the eigenvalue of complicated structures in which the limit state equation is implicitly expressed is formulated and applied to the buckling analysis by combining probabilistic finite element method with direct differential method which is a kind of sensitivity analysis technique. Also, the probability of buckling failure is calculated by combining classical reliability techniques such a MVFOSM and AFOSM. As random variables external load, elastic modulus, sectional moment of inertia and member length are chosen and Parkinson's iteration algorithm in AFOSM is used. The accuracy of the results by this study is verified by comparing the results with the crude Monte Carlo simulation and Importance Sampling Method. Through the case study of some structures the important aspects of buckling reliability analysis are discussed.

• Journal of Korea Water Resources Association
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• v.30 no.3
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• pp.269-278
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• 1997

Operating rules, the basic principle of reservoir operation, are mostly developed from maximum or minimum, mean inflow series so that those rules cannot be used in practical operating situations to estimate the expected benefits or provide the operating policies for uncertainty conditions. Many operating rules based on the deterministic method that considers all operation variables including inflows as known variables can not reflect to uncertainties of inflow variations. Explicit operating rules can be developed for improving the weakness. In this method, stochastic trend of inflow series, one of the reservoir operation variables, can be directly method, the stochastic technique was applied to develop reservoir operating rule. In this study, stochastic dynamic programming using the concepts was applied to develop optimal operating rule for the Chungju reservoir system. The developed operating rules are regarded as a practical usage because the operating policy is following up the basic concept of Lag-1 Markov except for flood season. This method can provide reservoir operating rule using the previous stage's inflow and the current stage's beginning storage when the current stage's inflow cannot be predicted properly.