• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.391-402
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• 1994

One of the most important design concept for reinforced concrete structures is to achieve a ductile failure mode, and also moment redistribution for economic design is possible in case that adequate ductility is provided. Flexural ductility index is, therefore, used as a reference for possibility of moment redistribution as well as for prediction of flexural behavior of designed R.C. structures. Ductility index equations, however, provide approximate values due to the linear concrete compressive stress assumption at the tension steel yielding state. Theoretically more exact ductility index is calculated by a numerical analysis with the realistic stress-strain curves for concrete and steel to be compared with the result from tire ductility index equations. Variation of ductility index for the selected variables and the reasonable maximum tension steel ratio for doubly reinforced section are investigated. A moment-curvature curve model is also proposed for future research on moment redistribution.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.297-300
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• 2008

Friction coefficients of the prestressing tendon are the basic information required to control the prestressing force introduced to PSC structure during jacking. However, the friction coefficients show considerable differences depending on the specifications, causing much confusion to designers. In this study, a procedure is proposed that can be used to estimate the wobble and curvature friction coefficients from field data and classical theory related to the friction. The procedure is applied to two PSC girder bridges with various tendon profiles. The resulting values are compared with those presented in some specifications and assumed in jacking. The resulting wobble friction coefficients are not as small as those presented in AASHTO specifications but are more or less similar to the lower limit of domestic standards, while the curvature friction coefficients approach or slightly exceed the upper limit of the same standards.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.11
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• pp.5979-5986
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• 2013

This study carried out a geometrical nonlinear dynamic analysis of laminated composite shell structures. Based on the first-order shear deformation shell theory and nonlinear formulation of Sanders, the Newmark method and Newton-Raphson iteration are used for dynamic solution considering nonlinear effects. The effects of radius, fiber angles, and layup sequences on the nonlinear dynamic response for various parameters are studied using a nonlinear dynamic finite element program developed for this study. The several numerical results were in good agreement with those reported by other investigators for square composite plates, and the new results reported in this paper show the significant interactions between the radius, fiber angles and layup sequence in the laminate. Key observation points are discussed and a brief design guideline of laminated composite shells is given.

• Computational Structural Engineering
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• v.3 no.4
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• pp.113-122
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• 1990

An analytical simulation of the flexural behavior of SFRC beam has been illustrated. Curvature distributions and crack opening in critical region were taken into account. Compressive and tensile constitutive models which express post-peak behavior of SFRC with stress-crack opening relationships were incorporated in simulating nonlinear flexural behavior of the beam. The model was able to predict test results with reasonable accuracy. Behavior of the critical section and effects of different factors m the flexural behavior of SFRC beam were investigated. Simple observation and statistical approach have been made in selecting most influential parameters in flexural behavior of SFRC.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.04b
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• pp.44-48
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• 1993

산업현장에서부터 실생활용품에 이르기까지 각종판재를 소재로하여 제작하는 가공품은 종류나 수가 매우 많다고 할수 있다. 이러한 제품들을 제작 하기 위해 여러단계의 성형 공정을 거치게 되며 원만한 성형공정 을 수행하기 위한 적절한 판재성형 제어방법으로써 다이곡률 반경의 변화나 블랭크홀딩가압정도의 부분적 변화로 드로잉률을 향상시키는 방법도 있으나 이보다 판재의 성형공정 제어방법에서 공구사이 상하에 비드 를 설치하여 판재를 성형할 경우 성형공정후 제품의 두께 분포가 비교적 균일해지고 드로잉의 마찰저항을 부분적으로 증가시키며 판재성형중 미끄럼 저항의 균형을 이루어 성형시킬 판소재가 절감도며 또한 성형중 주름을 억재하여 드로잉률을 향상시킨다. 다른 방법에 비해 비드는 설차가 간단해서 적절한 형상의 bead set을 선정하여 산업현장에서 실제 사용하고 있으며 또한 소재가 비드를 통과한후 탄성역에서 소성역으로 전환되기에 성형공정 이후 스프링백 현상으로인한 제품형상의 치수가 변하는 현상을 방지하는 효과도 기대할수 있다. 따라서 본 연구에서는 자동차용판재인 아연도금피막 강판으로 실험한 결과와 비드 이론식을 고찰해 보고자 한다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.2
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• pp.240-249
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• 1985

여러 가지 조건하에서 한쪽면만 이온질화 처리된 SCM4 의 평판을 모델로 하여 질화층의 기계적 성질과 잔류응력을 연구하였다. 질화층에서의 재료의 성질은 질소함량분포에 비례하여 변할 것이 라는 가정하에 외팔보의 굽힘과 온도-곡률의 관계를 구하는 이론적 모델을 정립하고 이에 따른 간접적 실험방법을 제시하였다. 질화층 표면에서의 선팽창 계수는 질화되지 않은 코어의 값에 비 해 2내지 12% 증가를 보였고 탄성계수는 50내지 700%증가를 보였다. 질화로 인한 축방향 팽창은 변형도로 약 0.002를 얻었다. 상온에서의 코어의 최대인장 잔류응력은 2내지 25Kg/mm$^{2}$이 며, 질화층표면에서 일어나는 최대압축잔류응력은 질화조건에 따라 50내지 300Kg/mm$^{2}$을 얻었다.

• Computational Structural Engineering
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• v.11 no.4
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• pp.239-251
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• 1998

본 연구에서는 비대칭 박벽단면을 갖는 곡선보의 안정성해석을 수행할 수 있는 이론 및 엄밀해를 제시하기 위하여, 3차원 연속체로부터 유도된 평형방정식으로부터 선형화된 가상일의 원리를 적용하였다. 박벽단면의 구속된 ？(warping)과 곡률효과를 고려하고 유한한 회전각의 2차항을 포함하는 곡선보의 변위장을 도입하여 단면에 대해 적분함으로써 도심축에 대한 박벽 곡선보의 총포텐셜에너지를 유도하였다. 또한, 단순지지되고 일축대칭 단면을 갖는 박벽원형 곡선보의 면내 및 면외좌굴에 대한 엄밀해를 유도하기 위하여, 면내에 대해서는 균일압축을 받는 원형아치의 역대칭 좌굴모드에 대한 좌굴하중을 유도하고 면외좌굴에 대해서는 균일압축 및 순수휨을 받는 아치의 처짐함수를 가정하여 곡선보의 횡좌굴하중에 대한 일반해를 제시하였다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.8
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• pp.816-822
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• 1992

In this paper, propagation characteristics of trapezoidal-shaped segmented core single mode fibers is investigated theoretically as a function of relative Index difference ratio( =p) under the condition of zero dispersion at i=1.,isrm, and bending loss of trape zoidalshaped segmented core single mode fiber is greatly decreased less than that of conventional single mode fibers ( triangular Index, dual shape core). And mode field distribution In core Is confined 2H% stronger than that of a tapezoidal Index fiber In addition, the advantages of trapezoldal-shaped segmented core fibers are compared with t hose of conventional triangular -shaped segmented core fibers.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.100-107
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• 2018

The objective of this study is to assess the strengthening effects of fiber reinforced polymer(FRP) sheets such as Carbon fiber, Glass fiber, and PET(polyethylene terephthalate) on reinforced concrete flexural members. Variables of theoretical analysis are types of strengthening materials, material properties and amount of strengthening materials. A virtual flexural member without FRP sheets was created as a control specimen to understand the structural behavior of the non-strengthened specimen in terms of elastic and ultimate cross section. In total, 11 specimens including one non-strengthened and ten strengthened specimens were investigated. Various variables such as types of strengthening, strengthening properties, and amount of strengthening were studied to compare the behavior of the control specimen with those of strengthened specimens with regard to moment-curvature relationship. Results of theoretical analysis showed that the moment capacity of strengthened specimens was superior to that of the control specimen. However, the control specimen indicated the best ductility among all the specimens. As the amount of strengthening increased, flexural performance was improved. Furthermore, the results indicated that the ductile effect of members was affected by the ultimate strain of FRP sheets. The strengthening effect on the damaged member was similar to that on the non-damaged one since there was less than 10% difference in terms of flexural strength and ductility. Therefore, even if a damaged member is treated as non-damaged for analysis there is probably no noticeable difference.