• Structural Engineering and Mechanics
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• 제12권2호
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• pp.201-214
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• 2001

Four finite element (FE) models are examined to find the one that best estimates moment-rotation characteristics of top- and seat-angle with double web-angle connections. To efficiently simulate the real behavior of connections, finite element analyses are performed with following considerations: 1) all components of connection (beam, column, angles and bolts) are discretized by eight-node solid elements; 2) shapes of bolt shank, head, and nut are precisely taken into account in modeling; and 3) contact surface algorithm is applied as boundary condition. To improve accuracy in predicting moment-rotation behavior of a connection, bolt pretension is introduced before the corresponding connection moment being surcharged. The experimental results are used to investigate the applicability of FE method and to check the performance of three-parameter power model by making comparison among their moment-rotation behaviors and by assessment of deformation and stress distribution patterns at the final stage of loading. This research exposes two important features: (1) the FE method has tremendous potential for connection modeling for both monotonic and cyclic loading; and (2) the power model is able to predict moment-rotation characteristics of semi-rigid connections with acceptable accuracy.

• 약학회지
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• 제45권6호
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• pp.623-633
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• 2001

Various bupivacaine-loaded microspheres were prepared using poly(d,1-lactide) (PLA) and poly(d,1-lactic-co-glycolide) (PLGA) by a solvent evaporation method for the sustained release of drug. The effects of process conditions such as drug loading, polymer type and solvent type on the characteristics of microspheres were investigated. The prepared microspheres were characterized for their drug loading, size distribution, surface morphology and release kinetics. Drug loading efficiency and yield of PLGA micro- spheres were higher than those of PLA microspheres. The prepared microspheres had an average particle size below 5${\mu}{\textrm}{m}$. The particle size range of microspheres was 1.65~2.24${\mu}{\textrm}{m}$. As a result of SEM, the particle size of PLA microspheres was smaller than that of PLGA microspheres. In morphology studies, microspheres showed a spherical shape and smooth surface in all process conditions. In thermal analysis, bupivacaine-loaded microspheres showed no peaks originating from bupivacaine. This suggested that bupivacaine base was molecular-dispersed in the polymer matrix of microspheres. The release pattern of the drug from microspheres was evaluated for 96 hours. The initial burst release of bupivacaine base decreased with increasing the molecular weight of PLGA, and the drug from microspheres released slowly. In conclusion, bupivacaine-loaded microspheres were successfully prepared from poly(d,1-lactide) and poly (d,1- lactic-co-glycolide) polymers with different molecular weights allowing control of the release rate.

• 대한토목학회논문집
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• 제26권3D호
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• pp.435-444
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• 2006

본 논문은 AREA법을 사용하는 줄눈 콘크리트포장의 평가에 3차원 유한요소모델을 사용하는 경우 나타나는 특성을 조사하는데 목적이 있다. 이를 위해 실제 콘크리트포장을 거동을 반영할 수 있는 3차원 유한요소모델을 구축하였고 2차원 모델과 비교한 후 민감도 분석을 수행하였다. ILLISLAB을 사용한 2차원 모델과 비교하였고 하중형태의 영향 보다 하중재하 지점의 자체수축과 기층모델에 따른 영향을 더 많이 받는 것으로 나타났다. 3차원 모델에서 비선형 온도구배를 선형 온도구배로 변화시키는 경우 발생하는 영향을 조사하였고 큰 차이를 보이지는 않았으나 지반 탄성계수가 작아질수록 더 많은 차이를 보였다. 동적하중에 의한 처짐을 구하였고 정적하중에 의한 처짐과 비교한 결과 낮은 지반 탄성계수에서는 동적하중에 의한 처짐이 작게 나타났으나 높은 지반 탄성계수에서는 동적하중에 의한 처짐이 크게 나타났다. 동적하중에 의한 처짐 이력을 구하고 AREA법을 이용하여 동적지지력과 탄성계수를 역산하였으며 이를 정적 처짐에 의한 결과와 비교하였다. 그 결과 동적지지력의 경우 정적 해석에 의한 값보다 동적해석에 의한 값이 낮게 나타났고 탄성계수의 경우 반대의 경향을 나타내어 현장에서 AREA법을 사용하는 경우 나타나는 평가결과의 특성을 설명하는 것으로 판단되었다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 봄 학술발표회 논문집
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• pp.313-321
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• 1999

To design steel box girder bridge, designers have taken the classical load distribution coefficient methods. Due to the rapidly developing computer technique, steel box girder bridge is simply modeled as grillage method for analyzing the girder, or as fully finite element method for more accurate and detailed analysis. Recently, cruciform space frame method is developed for modeling and analyzing it more simply and easily compared with finite element method. So, this study for the examination of upper methods' characteristics loaded unit moment load and analyzed the distortional deflection with shell element method and cruciform space frame method, and for three span three girder steel box bridge, loading DB-24 loads, analyzed it by upper methods and compared the results.

• International Journal of Railway
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• 제3권1호
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• pp.14-18
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• 2010

This paper describes design and characteristic analysis of long primary type linear synchronous motor (LSM) for high speed train system. LSM is designed using loading distribution method and magnetic equivalent circuit. For characteristic analysis of LSM, analytical and numerical methods are applied. Analytical method for solving the magnetic field distribution of the analytic model is based on the Maxwell’s equations. Using the characteristic equation and magnetic equivalent circuit, we analyze the effect of variation of parameters, and then we validate the result by comparing with numerical method by finite element method (FEM). We compare the analytical method with numerical method for analyzing the effect by variable parameters. This result will be useful of design and forecast of performance without FEM.

• 대한치과기공학회지
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• 제29권1호
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• pp.93-101
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• 2007

The purpose of this study is to evaluate the effect of three different oblique mechanical loading to occlusal surfaces of posterior implant partial dentures on the stress distributions in surrounding bone, using 3-dimensional finite element method. A 3-dimensional finite element model of a posterior implant partial dentures composed of three unit implants, simplified 3 gold alloy crown and supporting bone was developed according to the design of AVANA self tapping implant for this study. Three kinds of surface distributed oblique loads(300 N) are applied to following occlusal surfaces in the three crowns; 1) All occlusal surfaces in the three crown(load of 300 N was shared to three crown), 2) Occlusal surface of centered crown (load of 300 N was applied to a centered crown), 3) Occlusal surface of proximal crown(load of 300 N was applied to a distal proximal crown). In the results, 141 MPa of maximum von Mises stress was calculated at third loading condition and 98 MPa of minimum von Mises stress was calculated at first loading condition. From the results, location and type of occlusive loading conditions are important for the safety of supporting bone.

• 한국항공우주학회지
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• 제33권2호
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• pp.39-45
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• 2005

본 연구에서는 현재 일반 프로펠러 항공기에 사용 중인 둥근 팁 형상을 갖는 Hartzell 사 제작 프로펠러에 대해서 두께소음과 하중소음에 대한 예측을 시도하였다. 음향장 해석에 앞서서 프로펠러 표면상에 존재하는 압력분포는 자유후류 패널 방법과 비정상 베르누이 방정식을 이용하여 구하였다. 음향장 해석을 위해서는 FW-H의 음향상사 법칙을 적용하였다. 주어진 프로펠러 형상과 운전 조건에 대한 소음 예측으로부터 두께소음은 프로펠러 회전면을 기준으로 전방과 후방이 서로 비슷한 면대칭 분포를 갖는 반면에, 하중소음은 프로펠러 후방의 소음이 전방에 비해서 더 크게 나오는 결과를 보여주었다. 일반적인 운전조건에서는 전반적으로 하중소음이 두께소음보다 지배적인 결과를 보여주었다.

• Computers and Concrete
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• 제4권5호
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• pp.331-346
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• 2007

A computer program was developed to analyze the non-linear, cyclic flexural performance of reinforced concrete structural members under various types of loading paths including non-sequential variations in axial load. This performance is significantly affected by the loading history. Different monotonic material models as well as hysteresis rules for confined and unconfined concrete and steel, some developed and calibrated against test results on material samples, were implemented in a fiber-based moment-curvature and in turn force-deflection analysis. One of the assumptions on curvature distribution along the member was based on a method developed to address the variation of the plastic hinge length as a result of loading pattern. Functionality of the program was verified by reproduction of analytical results obtained by others for several cases, and accuracy of the analytical process and the implemented models were evaluated against the experimental results from large-scale reinforced concrete columns tested under the analyzed loading cases. While the program can be used to predict the response of a member under a certain loading pattern, it can also be used to examine various analytical models and methods or refine a custom material model against test data.

• Computers and Concrete
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• 제19권2호
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• pp.143-152
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• 2017

This paper has numerically investigated the changes of loading-induced stress in concrete with the corrosion time in the sulfate-containing environment. Firstly, based on Fick's law and reaction kinetics, a diffusion-reaction equation of sulfate ion in concrete is proposed, and it is numerically solved to obtain the spatial and temporal distribution of sulfate ion concentration in concrete by the finite difference method. Secondly, by fitting the existed experimental data of concrete in sodium sulfate solutions, the chemical damage of concrete associated with sulfate ion concentration and corrosion time is quantitatively presented. Thirdly, depending on the plastic-damage mechanics, while considering the influence of sulfate attack on concrete properties, a simplified chemo-mechanical damage model, with stress-based plasticity and strain-driven damage, for concrete under axial loading and sulfate attack is determined by introducing the chemical damage degree. Finally, an axially compressed concrete prism immersed into the sodium sulfate solution is regarded as an object to investigate the time-varying stress in concrete subjected to the couplings of axial loading and sulfate attack.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3892-3898
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• 1996

In this study, the prediction of the fatigue life as well as the extimation of the characteristics of fatigue cumulative damage on GFRP under random loading were performed. The constant amplitude tests and the ramdom loading test were carried on notched GFRP specimens with a circular hole. Random waves were generated with a micro-computer and had wide band spectra. Since it is useful that the prediction of fatigue life ot the given load sequences is based on S-N curves under constant amplitude loading, the estimation of equivalent stress is done on every random waves. The equivalent stress wasat first estimated by Miner's rule and then by the proposed model which was based on Hashin-Rotem's comulative damage theory regarding nonlinear fatigue cumulative damage behavior. The fatigue lives were predicted from each equivalent stress evaluated. And each predicted fatigue llife was compared with experimental results. The number of cycles of random loads were counted by mean-cross counting method. The reuslts showed that the fatigue life predicted by proposed model was correlated well with the experimental results in comparison with Miner's model.