• Journal of Magnetics
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• 제21권1호
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• pp.115-124
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• 2016

The present study analyzes T1 TSE and T1 slice sel. IR (dark_fluid) signal strength according to the degree of gadolinium contrast agent dilution and analyzes the turbo factors with regard to changes in the maximum and overall signal strength to study correlations between changes and signal-to-noise ratios (SNRs) and compare peak-to-peak SNR (PSNR) enhancement in order to improve the quality of T1-weighted images. Enhancement TR (600 msec) evaluated to determine the T1 TSE turbo factor and obtain the maximum signal strength, T1WI were used sequentially to experiment with turbo factors_1-4. T1 slice sel. IR (dark-fluid) was used to sequentially test turbo factors_2-5 but not turbo factor_1 at a TR (1500 msec) and compare data at an increase in T1 of 900 msec. The T1 TSE was reduced according to the contrast agent concentration. Phantom signal strength increased, whereas turbo factors_1-4 exhibited maximum signal strength at a concentration of 3 mmol, followed by a gradual decrease. In the turbo factors_2-5, the signal strength increased sharply to maximum signal strength at 0.7 mmol, followed by a reduction. T1 TSE had a greater maximum signal strength than did T1 slice sel. IR (dark_fluid). A comparison of SNR found that T1 TSE imaging was superior (33.3 dB) in turbo factor_1 and T1 slice sel. IR (dark_fluid) was highest (33.9 dB) at turbo factor_5. A PSNR comparison analysis was not sufficient to distinguish between the images obtained with both techniques at 30 dB or higher under all experimental conditions.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.225-226
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• 2009

Day by day, concrete buildings and structure became high-rising and magnificently vast scheduled, as contributed from the development of improved equipments that suitable to specific construction works and high qualitied Material, the durability of the concrete was highly improved. The temporary elastic reduction occur at vertical members such as walls and columns under vertical loads. Specially, inelastic reduction such as creep and shrinkage occur long termly with elastic one in case of reinforced concrete members. Generally, creep and shrinkage depend on time and this is affected by concrete strength, concrete type, member size, steel ratio, and relative humidity. And elastic reduction rely on time, too because concrete is loaded before revelation of perfect strength in terms of construction conditions. So, tests on mechanical properties of concrete certainly need in order to apply to construction by forecasting an amount of reduction caused by the complex factors. Therefore, in this study the tests on creep, shrinkage are carried out to offer basic data for predicting an amount of long-term Properties at the concrete columns of an object structure, and results of the tests are described.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1997년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 1997
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• pp.193-200
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• 1997

Current seismic design code is based of the assumption that the designed structures would be behaved inelastically during a severe earthquake ground motion. For this reason, seismic design forces calculated by seismic codes are much lower than the forces generated by design earthquakes which makes structures responding elastically. Present procedures for calculating seismic design forces are based on the use of elastic spectra reduced by a strength reduction factors known as "response modificaion factor". Because these factors were determined empirically, it is difficult to know how much inelastic behaviors of the structures exhibit. In this study, base shear forces required to maintain target ductility ratio were first calculated from nonlinear dynamic analysis on the single degree of freedom system. And then, base shear foeces specified in seismic design code compare with above results. If the strength(base shear) required strength should be filled by overstrength and/or redundancy. Therefore, overstrength of moment resisting frame structure will be estimated from the results of static nonlinear analysis(push-over analysis).analysis).

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.373-378
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• 2000

The objective of this study was to investigate the influence the influence of theoretical void ratio(T.V.R), grading of aggregate and curing method on the strength and water permeability of porous concrete, and the reduction proportion of water permeability by these factors. The results of the study showed that its strength and water permeability were greatly depended on the T.V.R and grading of aggregate, but didn't on the curing method. And, when the T.V.R and grading of aggregate were increased, the reduction proportion of water permeability was small. As the relation ship between its physical properties and non-destruction test values was very high, its use for the estimation of the physical properties will be useful.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 봄 학술발표회 논문집
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• pp.293-298
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• 1995

The strength of shear connectors embedded in lightweight concrete slab with deck plate is influenced by various factors of deck plate, shear conncetor and concrete. Generally, it is reported that the strength of shear connector in lightweight concrete decreases in comparison with that in normal concrete. So this paper is to use compressive strength of lilghtweight concrete, width-height ratio of deck plate, and cross sectional area of shear conncetor as variables, to evaluate the strength of shear conncetors in composite beam of steel and lilghtweight concrete slabs with deck plate, and then to suggest the reasonable strength equation by comparing the push-out test results with establixhed strength formula. As the result of 24 specimens test, in case of lightweight concrete slab with deck plate, it has showed that in the same strength, the strength of shear connector decreased about 10~20% in comparison with that in normal concrete. In spite of lightweight concrete, the test results were closely approached the established strength formula of shear connector using Fisher's reduction coefficient.

• 콘크리트학회논문집
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• 제22권4호
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• pp.451-460
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• 2010

리모델링에는 여러 형태가 있을 수 있다. 그 중 건축주나 리모델링 수행자가 선호하는 방법이 두 개의 주거 공간을 하나로 만들어 평면 확장을 목표로 하는 세대 병합형 리모델링이다. 그러나 이러한 방법을 현재 국내에서 리모델링 대상이 되고 있는 벽식 구조의 아파트에 적용할 경우 주요 횡력 저항 요소인 전단벽에 큰 손상을 가하게 될 수 있다. 그러나 아직 이러한 주요 구조 부재인 철근콘크리트 전단벽에 개구부가 발생할 경우의 명확한 손상 정도를 정의 해주는 연구는 진행되고 있지 않은 실정이다. 현행 ACI 기준은 이러한 철근콘크리트 전단벽 내의 개구부에 대한 명확한 고려 방안을 제시하지 않고 있다. 반면 AIJ 기준은 철근콘크리트 전단벽 내부의 벽체에 대한 고려 방안으로 강도 저감률 $\gamma$를 제시하고 있다. 그러나 이 강도 저감률은 탄성 판 이론으로부터 제시된 것으로 철근콘크리트 부재에 있어서의 강도 저감률을 제대로 표현하지 못하고 있는 실정이다. 그러므로 이 연구에서는 AIJ에서 제시하고 있는 강도 저감률 $\gamma$에 대하여 현재까지 진행되었던 실험 결과에 대한 통계적 분석과 유한요소해석을 통한 변수 분석을 통해 개구부에 의한 강도 저감률에 대한 연구를 수행하였다. 통계적 분석 결과 현재 제시되어 있는 강도 저감률은 개구부의 벽체 면적에 대한 비율만을 변수로 설정하여 그 저감률이 실험 결과보다 크게 나타나고 있었다. 또한 개구부의 형상비를 면적과 통합적으로 고려하며 철근비에 대한 고려를 하지 못하는 것으로 나타났다. 이에, 기존의 실험 결과와 이를 토대로한 유한요소해석을 통한 변수분석을 수행하여 새로운 강도 저감률을 제안하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 추계 학술발표회
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• pp.196-203
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• 2008

Durability of geosynthetics for soil reinforcement is accounted for creep and creep rupture, installation damage and weathering, chemical and biological degradation. Among these, the long-term creep properties have been considered as the most important factors which are directly related to the failure of geosynthetic-reinforced soil(GRS). However, the creep test methods and strain limits are too various to compare the test results with each other. The most widely used test methods are conventional creep test, time-temperature superposition and stepped isothermal method as accelerated creep tests. Recently developed design guidelines recommend that creep-rupture curve be used to determine the creep reduction factor($RF_{CR}$) which is a conservative approach. In this study, the different creep test methods were compared and the creep reduction factors were estimated at different creep strain limits of 10% of total creep strain and creep rupture. In order to minimize the impact of creep strain to the GRS structures, the various creep reduction factors using different creep test methods should be investigated and then the most appropriated one should be selected for incorporating into the design.

• 한국지반공학회논문집
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• 제19권5호
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• pp.163-173
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• 2003

본 연구에서는 억지말뚝으로 보강된 사면에서 한계평형 해석법과 3차원 해석 결과를 비교 분석하였다. 특히, 유한차분법을 이용한 FLAC 3D를 바탕으로 하는 커플링 해석에 주안점을 두었으며, FLAC을 이용하여 전단강도감소기법에 따른 보강사면의 안전율을 계산하기 위해 FLAC의 내장언어인 FISH를 이용하여 작성하였다. 커플링 해석에서 억지말뚝에 의한 안정화된 사면을 해석하기 위해 말뚝의 거동과 사면안정을 동시에 고려하였다. 따라서 본 연구에서는 이 두 방법을 적용하여 일렬 억지말뚝이 사면선단, 중앙부, 정부에 위치할 경우에 있어서 각각의 활동 파괴면 및 안전율을 비교 분석하였으며 강도정수 감소법을 적용한 해석기법의 적용성과 타당성에 대한 분석을 수행하였다.

• 한국지반공학회논문집
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• 제19권4호
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• pp.65-74
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• 2003

본 논문에서는 사면안정해석에 있어서의 유한요소법과 한계평형법의 결과를 나타내었다 해석의 타당성을 부여하기 위하여 유한요소법과 한계평형법에 의한 안전율을 비교하였으며, 각각의 방법에 의한 안전율이 잘 일치됨을 보여 전단강도감소기법을 사용한 유한요소해석이 사면안정해석에 있어서 효과적으로 사용될 수 있음을 확인하였다. 구성 법칙, 사면의 경사각, 흐름법칙, 그리고 유한요소망의 이산화에 따른 일련의 유한요소해석을 실시한 결과, 전단강도감소기법에 근거한 유한요소해석법은 안전율에 관하여 합리적인 결과를 제공할 수 있음을 확인하였고 유한요소해석결과는 구성법칙과 흐름법칙의 선택에 의해 상당한 영향을 받을 수 있음을 알 수 있다.

• Structural Engineering and Mechanics
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• 제12권3호
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• pp.249-266
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• 2001

Current seismic design provisions allow structures to deform into inelastic range during design level earthquakes since the chance to meet such event is quite rare. For this purpose, design base shear is defined in current seismic design provisions as the value of elastic seismic shear force divided by strength reduction factor, R (${\geq}1$). Strength reduction factor generally consists of four different factors, which can account for ductility capacity, overstrength, damping, and redundancy inherent in structures respectively. In this study, R factor is assumed to account for only the ductility rather than overstrength, damping, and redundancy. The R factor considering ductility is called "ductility factor" ($R_{\mu}$). This study proposes ductility factor with correction factor, C, which can account for dynamic P-${\Delta}$ effect. Correction factor, C is established as the functional form since it requires computational efforts and time for calculating this factor. From the statistical study using the results of nonlinear dynamic analysis for 40 earthquake ground motions (EQGM) it is shown that the dependence of C factor on structural period is weak, whereas C factor is strongly dependant on the change of ductility ratio and stability coefficient. To propose the functional form of C factor statistical study is carried out using 79,920 nonlinear dynamic analysis results for different combination of parameters and 40 EQGM.