• Magazine of the Korea Concrete Institute
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• v.1 no.1
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• pp.87-94
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• 1989

철근콘크리트 뼈대구조와 같이 설계변수가 과다하고, 제약조건식이 복잡한 구조물의 최적화를 위하여는 구조물을 여러개의 부분구조물로 분할하여 최적해를 구하는 분할법이 많이 사용되고 있다. 그러나 기존의 분할법에 의한 최적화는 구조해석과정과 고정된 부재력에대한 단면설계변수의 부분최적화 과정만으로 이루어지기 때문에, 최적해를 구하려면 반복적인 재해석과정만을 수행하지 않으면 안된다. 따라서 본 연구에서는 다단계분할법에 의하여 철근콘크리트 뼈대구조의 최적화 문제를 3단계로 형성하고, 분할된 부분최적화문제의 최적화시 전체구조의 강성 및 부재력 변화가 반영되어 부분 구조물의 결합을 유지시킬 수 있는 최적화 알고리즘을 제안하였다. 최적화 문제에서 설계변수로는 단면의 크기, 철근량, 모멘트 재분배율등을 취하고,목적함수는 경비함수, 제약조건으로는 강도설계법에 의한 부재강도, 시방서의 요구사항등을 고려하여 문제를 형성하였다. 본 연구에서 개발한 다단계 최적화과정의 첫째 단계에서는 탄성해석에 의하여 재분배모멘트의 설계공간을 형성한다. 이 때 부재력변화량추정(forece approximation technique)에 의하여 단면치수의 변화에 따른 부재력의 변화를 제약조건식 내에 포함시킬 수 있도록 하였다. 둘째 단면에서는 첫째 단계에서 구한 부재력변화량추정이 포함된 제약조건식 내에서 무제약최소화기법에 의하여 단면치수를 최적화하도록 하였다. 셋째 단계에서는 재분배 모멘트를 최적화하였으며, 이 때 재분배모멘트의 변화에 따른 단면설계 변수의 변화는 둘째 단계에서 구한 설계민감도(design sensitivity)를 이용하여 반영시키도록 하였다. 제안된 알고리즘을 1층 2경간 및 2층 1경간 뼈대구조에 적용하여 알고리즘의 타당성과 효율성을 입증하였다. 따라서 본 연구의 알고리즘은 철근 콘크리트 뼈대구조의 최적설계에 안정성있게 적용할 수 있을 것으로 판단된다.

• Journal of the Korea Concrete Institute
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• v.14 no.6
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• pp.892-899
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• 2002

Among the methods for enhancement of load-carrying capacity on flexural concrete member, recently, a concept is being investigated which replaces the steel in a conventional reinforced concrete member with a fiber reinforced polymer(FRP) shell. This study focuses on modeling of the structural behavior of concrete surrounded with FRP shells in flexural bending members. A numerical model of fiber cross-sectional analysis is proposed to predict the stress and deformation state of the FRP shell and concrete. The stress-strain relationship of concrete confined by a FRP shell is formulated to be based on the constitutive law of concrete in multi-axial compressive stress state, in assuming that the compression response is dependent on the radial expansion of the concrete. To describe the FRP shell behavior, equivalent orthotropic properties of in-plane behavior from classical lamination theory are used. The present model is validated to compare with the experiments of 4-point bending tests of FRP shell concrete beam, and has well predicted the moment-curvature relationships of the members, axial and hoop strains in the section, and the enhancement of confinement effect in concrete surrounded by FRP shell.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.41-50
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• 1989

A basic formulation of the panel method, which is based on the potential field formulation, is reviewed for the case of two-dimensional hydrofoil problems. Numerical procedures to improve the computational efficiency of the panel method are suggested. By investigating local behavior of the flow around the trailing edge, a wedge type Kutta condition is formulated. By subdividing the trailing edge panels, where dipole strengths of the subdivided panels follow the local behavior of the potential values of the flow outside a wedge, the circulation around a hydrofoil is calculated accurately with a relatively small number of panels. The subdividing technique to improve the accuracy of the numerical Kutta condition is proved to be efficient. A local behavior of the flow around the leading edge is also investigated. By matching the flow around the leading edge with that around a parabola, a very accurate velocity distribution is obtained with relatively small number of panels. An accurate prediction of the stagnation point and the pressure distribution near the leading edge may contribute to improve the accuracy of cavity predictions and boundary layer calculations around hydrofoils.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.60-67
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• 2019

In general, a reinforced concrete slabs are known to have a high fire resistance performance due to thermal properties of concrete materials. However, according to previous research, the thermal behavior of voided slabs is reported to be different from that of conventional RC solid slabs, and the differences seem to be caused by the air layer formed inside the voided slab. Therefore, it is difficult to estimate the temperature distribution of the voided slab under fire by using the existing methods that do not take into account the air layer inside the voided slab. In this study, a numerical analysis model was proposed to estimate the temperature distribution of voided slabs under fire, and evaluated. Heat transfer of slabs under fire is generally caused by conduction, convection and radiation, and time-dependent temperature changes of slab can be determined considering these phenomena. This study proposed a numerical method to estimate the temperature distribution of voided slabs under fire based on a finite difference method in which a cross-section of the slab is divided into a number of layers. This method is also developed to allow consideration of heat transfer through convection and radiation in air layer inside of slabs. In addition, the proposed model was also validated by comparison with the experimental results, and the results showed that the proposed model appropriately predicts the temperature distribution of voided slabs under fire.

• Journal of the Korean Geotechnical Society
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• v.40 no.4
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• pp.105-112
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• 2024

Increased extreme weather conditions have led to a rise in flood damage to domestic rivers in Korea. This in turn has caused increased discharge through the structures and foundations of submerged weirs, leading to piping phenomena that can destroy these weirs. Therefore, extensive research into increased infiltration rates is necessary for the management and design of submerged weirs. In this study, seepage discharges were calculated and comparatively analyzed for weirs by varying the depth of the stratum and the length and location of sheet piles using numerical analysis, the fragment method, and the Polubarino-Kochina method. The results showed that the seepage discharge decreased as S/T increased and tended to increase as X/b increased. Changes in the length of the sheet pile had a greater impact on the infiltration rate than changes in the position of the sheet pile. Therefore, it is considered that installing longer sheet piles upstream can decrease the seepage discharge, enabling a safer design against piping in the weir design.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.7A
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• pp.1006-1016
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• 2000

This study is to segment white matter, gray matter, and cerebrospinal fluid(CSF) on a brain MR image and to calculate the volume of each. First, after removing the background on a brain MR image, we segmented the whole region of a brain from a skull and a fat layer. Then, we calculated the partial volume of each component, which was present in scanning finite thickness, with the arithmetical analysis of gray value from the internal region of a brain showing the blurring effects on the basis of the MR image forming principle. Calculated partial volumes of white matter, gray matter and CSF were used to determine the threshold for the segmentation of each component on a brain MR image showing the blurring effects. Finally, the volumes of segmented white matter, gray matter, and CSF were calculated. The result of this study can be used as the objective diagnostic method to determine the degree of brain atrophy of patients who have neurodegenerative diseases such as Alzheimer's disease and cerebral palsy.