• Computational Structural Engineering
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• v.8 no.4
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• pp.65-74
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• 1995

Direct method developed for the inelastic analysis of planar frames subjected to monotonic loads is extended to cyclic loads. Two frame elements for Direct Method(inelastic truss and inelastic beam) are developed. The accuracy and reliability of the preposed method is verified by comparing the analysis results of example with step-by-step analysis. Direct Method is superior to Step-by-step analysis in view of reliability of solution and analysis cost.

• Journal of computational fluids engineering
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• v.1 no.1
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• pp.142-149
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• 1996

이차원 노즐을 통하여 저밀도 환경으로 팽창하는 희박류의 분석에 있어서 불연속좌표법과 결합된 유한차분법(finite-difference method coupled with the discrete-ordinate method, FDDO)과 직접모사법(direct-simulation Monte-Carlo method, DSMC)이 비교되었다. FDDO를 이용한 분석에서는 충돌적분모델을 도입하여 간단해진 볼츠만식(Boltzmann equation)이 불연속좌표법을 이용하여 물리적 공간에서는 연속이나 분자속도 공간에서는 불연속좌표로 표시되는 편미분방정식군으로 변환되어 유한차분법에의하여 수치해석 되었다. 직접모사법에서는 분자모델로 가변강구모델(variable hard sphere model, VHS)이, 충돌샘플링모델로는 비시계수법(no time counter method, NTC)이 채택되었다. 전혀 다른 두 가지 방법에 의한 노즐 내부에서의 유체흐름 해석결과는 매우 잘 일치하였으며, 노즐 외부의 plume 영역에서는 FDDO에 의한 해석결과가 직접모사법에 의한 해석결과에 비하여 약간 느린 팽창을 보였다.

• Computational Structural Engineering
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• v.10 no.3
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• pp.46-51
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• 1997

본 고에서는 3차원 전선구조해석에 사용하는 직접구조해석기법 및 준직접구조해석기법에 대하여 설명하고 실선계산을 통하여 두 기법의 차이를 비교하였다. 직접구조해석은 준직접구조해석에 비하여 방대한 시간 및 노력이 요구되기 때문에 전선구조해석의 목적으로 사용하기에는 추천할 기법은 아니나 준직접구조해석의 검증, 피로해석 및 신로도 해석 등 응력의 확률 기준이 필요한 경우에는 필수적으로 수행해야 할 것이다.

• Journal of Korean Society of Steel Construction
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• v.22 no.4
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• pp.293-303
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• 2010

The purpose of this study was to evaluate the influence of the methods of application of the direct analysis method, using the load amplification factor suggested by the KBC 2009 design code, for the evaluation of frame stability. For this purpose, the direct analysis method was performed for three-story-one-bay and five-story-three-bay unbraced steel frames with various notional loads, bending stiffness reductions, and factor B2s. The results of the analyses were compared with the results of the second-order inelastic analysis to evaluate the influence of the applied methods. The scale of the frame, the axial load ratio, and the axial load distribution pattern were added to the main parameters to investigate the external effects. The research results showed that the influence of the methods of application of the direct analysis method is not significant in the case of the required axial strength and the application of the additional notional loads; and that the application of the factor B2 with the story stiffness concept to the direct analysis method is appropriate for the required flexural strength.

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.487-495
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• 2013

As the first step to suggest effective ways of using direct analysis method considering current situations of construction fields in Korea, analytical approach is used to verify direct analysis method which adapts initial imperfection limitation of Korean specification of building construction. The main analytical variables are size of frames, axial load ratio, axial load distribution, value of notional loads, location of notional loads, and applied method of notional loads. The results show that the use of initial imperfection limitation of Korean specification, L/700 is suitable, and the recommendable method to use direct analysis method is applied notional loads based on L/700 as minimum lateral load at each story, even if B2 is less than 1.5 and lateral loads exist.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.65-73
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• 2002

It has been recognized that the damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the nonlinear response is required. The methods available to the design engineer today are nonlinear time history analyses, monotonic static nonlinear analyses, or equivalent static analyses with simulated nonlinear influences. Some building codes propose the capacity spectrum method based on the nonlinear static analysis(pushover analysis) to determine the earthquake-induced demand given by the structure pushover curve. These procedures are conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method(NDSM) to evaluate seismic performance of structures, without iterative computations, given by the structural initial elastic period and yield strength from the pushover analysis, especially for MDF(multi degree of freedom) systems. The purpose of this paper is to investigate the accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters. The conclusions of this study are as follows; 1) NDSM is considered as practical method because the peak deformations of nonlinear system of MDF by NDSM are almost equal to the results of nonlinear time history analysis(NTHA) for various ground motions. 2) When the results of NDSM are compared with those of NTHA. mean of errors is the smallest in case of post-yielding stiffness factor 0.1, static force by MAD(modal adaptive distribution) and unloading stiffness degradation factor 0.2~0.3.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.5 s.45
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• pp.75-86
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• 2005

In performance-based design methods, it is clear that the evaluation of the nonlinear response is required. Analysis methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. The nonlinear time analysis is the most accurate method in computing the nonlinear response of structures, but it is time-consuming and necessitate more efforts. Some codes proposed the capacity spectrum method based on the nonlinear static analysis to determine earthquake-induced demand. The nonlinear direct spectrum method is proposed and studied to evaluate nonlinear response of structures, without iterative computations, given by the structural linear vibration period and yield strength from pushover analysis. The purpose of this paper is to compare the accuracy and the reliability of approximate nonlinear methods with respect to shear buildings and various earthquakes. The conclusions of this study are summarized as follows: 1) Linear capacity spectrum method may fail to find a convergent answer or make a divergence. Even if a convergent answer is found, it has a large error in some cases and the error varies greatly depending on earthquakes. 2) Although nonlinear capacity spectrum method need much less calculation than capacity spectrum method and find an answer in any case, it may be difficult to obtain an accurate answer and generally large error occurs. 3) The nonlinear direct spectrum method is thought to have good applicability because it produce relatively correct answer than other methods directly from pushover curves and nonlinear response spectrums without additional and iterative calculations.

• Tunnel and Underground Space
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• v.12 no.1
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• pp.37-42
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• 2002

A back analysis algorithm was developed to determine the major parameters for tunnel design; the elastic modulus(E) and the ratio of horizontal to vertical stress(K). The algorithm is based on direct search method and was coded by FISH language of FLAC, a commercial finite difference program. Developed code was applied on some models to verify the validity and estimate the efficiency of the algorithm. Verification by theoretical solutions and published results of Gens' research, was successful.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.4
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• pp.13-20
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• 1987

Methods of nonlinear structural design sensitivity analysis are developed in parallel with the nonlinear finite element structural analysis methods and numerically evaluated. Direct decomposition and iterative solution methods for the secant stiffness approach and direct use of tangent stiffness in the design sensitivity analysis phase are derived and presented as the methods of nonlinear structural analysis and design sensitivity analysis are closely related. From the considerations of theoretical and numerical behavior, the tangent stiffness approach is shown to be efficient as the intermediate results of structural analysis can be effectively used in the design sensitivity analysis stage.

• Journal of Korean Society of Steel Construction
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• v.21 no.6
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• pp.627-636
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• 2009

The purpose of this study was to evaluate the validity of the second-order analysis using the load amplification factor suggested by design codes. For this purpose, the first-order analysis with the B1 and B2 factors suggested by KBC 2005 and the direct analysis with the load amplification factor suggested by KBC 2009 (draft) were performed for three-story -one-bay and five-story-three-bay unbraced steel frames. The results of the analyses were compared with the results of the second-order inelastic analysis to evaluate the validity of the suggested methods. The main parameters of the analysis were the scale of the frame, the axial load ratio of the column, and the methods of analysis. The research results showedthat the method suggested by KBC 2005 does not properly consider the second-order effect under the high axial load ratio, but the direct analysis method suggested by KBC 2009 (draft) properly estimates the second-order effect without any serious problem.