• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.5
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• pp.23-29
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• 2008

This study investigates the dynamic instability of strength-limited bilinear single degree of freedom (SDF) systems under seismic excitation. The strength-limited bilinear hysteretic model best replicates the hysteretic behavior of the steel moment resisting frames. To estimate the dynamic instability of SDF systems, the collapse strength ratio is used, which is the yield-strength reduction factor when collapse occurs. Statistical studies are carried out to estimate median collapse strength ratios and those dispersions of strength-limited bilinear SDF systems with given natural periods, hardening stiffness ratios, post-capping stiffness ratios, ductility and damping ratios ranging from 2 to 20% subjected to 240 earthquake ground motions recorded on stiff soil sites. Equations to calculate median and standard deviation of collapse strength ratios in strength-limited bilinear SDF systems are obtained through nonlinear regression analysis. By using the proposed equations, this study estimated the probabilistic distribution of collapse strength ratios, and compared this with the exact values from which the accuracy of the proposed equations was verified.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.133-141
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• 2002

Isotropic rock and anisotropic rock have different tensile strength which has the greatest influence on rock failure. In this study, elastic modulus of anisotropic rock is obtained through uniaxial compression test, and tensile strength and tension failure behavior are analyzed through indirect tensile strength test. Stress concentration factor of a specimen at the center is obtained from anisotropic elastic modulus and strain by indirect tensile strength test. Theoretical solutions for tensile strength of isotropic and anisotropic rock are compared. Stress concentration factor of anisotropic rock is either higher or lower than isotropic rock depending on the inclination angle of bedding plane. The use of stress concentration factor of isotropic rock resulted in overestimation or underestimation of tensile strength.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.11a
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• pp.19-22
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• 2012

본 논문에서는 영상의 Intensity와 색상의 채도 분석을 통한 안개 강도 측정과 제거, 그리고 색상을 보정하는 방법을 제안한다. 이를 위해 영상에서 안개가 많은 지역과 적은 지역을 히스토그램을 통해 분석하고 안개 강도 맵을 만들어 안개의 양에 따라 안개를 제거한다. 안개로 인하여 악화된 영상의 색상은 HSI 공간에서 분석하여, 안개 강도에 따른 보정을 한다. 색상뿐만 아니라 전달량에 따른 Intensity를 보정하여 영상의 전체적인 밝기와 Contrast를 향상시킨다. 제안하는 기법은 기존의 기법들과 비교하여 색상의 편향성을 보정하여 가시성뿐만 아니라 영상 내에 색상이 자연스럽게 조화된 결과를 얻었다.

• Journal of Korea Technology Innovation Society
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• v.9 no.1
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• pp.1-25
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• 2006

Technological innovation is being recognized as a core capability of competitive advantage for sustainable growth of a company. In this regard, lots of research activities have been conducted on technological innovation and performance at firm level. Ihis study empirically investigates those relationship with cross-sectional and time-series data according to firm-specific characteristics along industry. Patent intensity, R&D intensity, and intangible asset intensity smoothing by firm size are used as proxy measures for explanation of performance with net income per employee. As a result with 162 high-tech firms for 11 years, it was found that high performances were positively related to patent and R&D intensity. Also, firms classified into 8 categories based on firm-specific technological innovation characteristics show difference upon performances. To sum up, firms that have high patent and R&D intensity demonstrate high performance compared to other firms.

• Journal of the Korea Convergence Society
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• v.13 no.4
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• pp.287-292
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• 2022

In this paper, the stochastic distribution of the springback amount is investigated for the stamping process of a U-channel shaped-product with ultra-high strength steel. Using the reliability-based design optimization technique (RBDO), stochastic distribution of process parameters is considered in the analysis including material properties and process variation. Quantification of the springback scatters is carried out with the statistical analysis method according to the material strength. It is found that the scattering amount of springback decreases while the amount of springback increases as the tensile strength of the blank material increases, which is investigated by analyzing the strain and stress distribution of the punch and die shoulder. It is noted that the proposed scheme is capable of predicting and responding to the unavoidable scattering of springback in the sheet metal forming process.

• Journal of the Korean Geotechnical Society
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• v.24 no.11
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• pp.157-166
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• 2008

To investigate the relationship between compressive strength ($q_u$) of Lightweight Air-mixed soil (LAS) and its physical deformation coefficient ($E_{50}$), a series of unconfined compressive tests have been performed on specimens of LAS according to various dredged soil types by percentage of sand, silt and clay. From the results it was found that the cement content ($C_i$) and unit weight (${\gamma}_m$) are most influence factors on strength, and percentage of sand, silt, clay by grain size analysis (KS F2302) have more effect on compressive strength than other physical properties of soil. It was also found that the rate of strength (a) increases with curing time, but it reduces with the increase of percentage of clay ($C_%$).

• The Journal of Engineering Geology
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• v.24 no.1
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• pp.101-110
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• 2014

This study presents the results of a regression analysis of the point-load strength ($I_{s(50)}$) and the uniaxial compressive strength (UCS) of granites in Korea. The regression was carried out for three cases using the least-squares method, reclassifying the granite samples based on their physical properties. The first regression analysis through the origin according to the weathering grade did not give a result with a sufficient degree of confidence, due to the small number of samples. However, the general trend of the correlation between UCS and $I_{s(50)}$according to weathering grade shows that the slope of the linear regression for weathered granite is steeper than that for fresh granite. The second analysis was a simple linear regression for all the granite samples using the least-squares method as well as a linear regression using the bootstrap resampling method in order to increase the confidence level and the accuracy of the regression results. The third regression considered the average strength of granite groups reclassified according to physical properties. These linear regression analyses yielded linear regression equations with slopes of 14 and small standard deviations being similar to values reported in previous studies on Korean granites, but whose intercept values range from 16 to 43 and have a larger standard deviation than those of the present study. In conclusion, it would be advisable to estimate UCS from $I_{s(50)}$, considering the error range derived from the deviation of the regression equations.

• Journal of the Korean Geotechnical Society
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• v.17 no.1
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• pp.5-13
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• 2001

강도 또는 변형 이방성은 층리진 최적암, 박층모양의 변성암, 균일하게 절 리가 나있는 암석에서 흔히 볼 수 있다(Amadei, 1982, 1996). 특히, 대구지역은 퇴적암의 일종인 셰일로 구성되어 층리면의 각도에 따라 역학적인 특성이 달리 산정되어져야 한다. 이에 본 연구에서는 층리면의 각도를 달리하여 시료를 성형한 후 각종 시험을 수행하였다. 그 결과 일축 압축강도는 수평면과 층리면이 이루는 각이 0$^{\circ}$, 90$^{\circ}$에서 최고 강도를, 60$^{\circ}$에서 최저 강도를 나타내었다. 또한 간접 인장시험과 점 하중시험, 탄성파시험에서는 90$^{\circ}$에서 최고값을, 0$^{\circ}$에서 최저값을 보였다. 그리고, 층리에 따른 퇴적압의 일축 압축강도를 간접 인장강도, 점하중강도와의 상관성을 분석하여 각각의 관계를 회귀분석을 통한 상관식으로 나타내었다. 추가적으로 층리에 따른 공학적특성을 정량적으로 나타내었다.

• Magazine of the Korea Concrete Institute
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• v.4 no.2
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• pp.111-118
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• 1992

본 연구는 실리카흄을 혼화재료로 사용하여 1200kg/$ extrm{cm}^2$정도의 초고강도 콘크리트를 제조하였으며 이에 대한 재료특성을 실험 및 보부재의 휨거동을 실험을 실시 비교 분석하였다. 재료특성 실험으로는 기본적인 강도 시험, 파괴음 측정에 의한 AE실험 그리고 수은압입법에 의한 세공실험을 실시하였다. 초고강도 콘크리트의 재료특성치는 ACI 363의 고강도 콘크리트 재료특성 결가보다 크게 나타났으며 압축강도와 미세공극량은 선형적으로 비례하였다. 보부재의 휨특성을 파악하기 위해 인장철근비 변화, 전단보강근의 유무 및 철근 표면형상의 변화 등을 실험인자로 하였으며 각각의 현상을 비교분석함으로써 균열성상에 따른 하중-변위 관계, 중립축 이동에 따른 부재거동 및 응력블록의 변화에 관하여 비교 고찰하였다. 초고강도 콘크리트 사용한 보부재의 경우 중립축 상승으로 단면의 압축영역은 매우 작아져 급격히 압축파괴되는 경향을 보였으며 응력블록 형태는 삼각형의 분포를 보였다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.101-101
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• 2022

IDF (Intensity-Duration-Frequency) 곡선에서 익숙하다시피 강우지속시간과 최대강우강도는 반비례한다. 그동안 이러한 관계를 살펴보는 것은 대개 수십 시간의 규모에 그쳤다. 이 연구에서는 과연 시계열에서 시간 규모를 계속 증가시키면서 해당 시간 동안의 최대강우강도가 어떻게 변하는지를 살펴보았다. 가능한 장기간의 강수관측이 이루어진 우리나라 24개 지점을 대상으로 시간 규모를 최장 한 세기까지 키우면서 최대강우강도의 변화를 분석하였다. 작은 시간 규모에서는 그 관계가 멱함수를 따르지만, 시간 규모가 점차 늘어나면서 최대강우강도는 설계 목적의 지속시간 범위에서 결정된 멱함수 또는 기존 IDF 곡선으로부터 외삽하기 어려워진다. 이러한 변화는 점차 정상 연강수량으로 점근하는 결과를 가져온다. 분석된 결과를 토대로 연 단위를 초과하는 지속시간에 걸친 최대강우강도의 감쇄를 적절하게 표현할 수 있는 함수식을 제시하였다.