• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.9
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• pp.3148-3154
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• 2010

This paper presents the probabilistic analysis for fatigue life of Glass/Epoxy laminates with impact-induced damage. For this, a series of impact tests were perfomed on the Glass/Epoxy laminates using instrumented impact testing machine. Then, tensile and fatigue tests carried out so as to generate post-impact residual strength and fatigue life. Two Parameter Weibull distribution was used to fit the residual strength and fatigue life data of Glass/Epoxy composite laminates. The residual strength was affected by impact energy and their variance decreased with increasing of impact energy. The fatigue life of impacted laminates was greatly reduced by impact energy and this trend depended on applied stress amplitude. Additionally, the variation of fatigue life was gradually decreased with the applied stress amplitude.

• Journal of the Korean Society for Railway
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• v.13 no.4
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• pp.371-375
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• 2010

In order to decide the strength requirement of the window glass for the high-speed train, the pressure change during the passage of the EMU type high-speed train has been numerically simulated. Based on the calculation results, the pressure difference between the inner and outer pressure of the cabin has been calculated to yield the amount of load acting on the window glass of the cabin. To simulate the pressure field generated by the high-speed train passing through the tunnel, computational fluid dynamics based on the axi-symmetric Navier-Stokes equation has been employed. The pressure change inside a train has been calculated using first order difference approximation based on a linear equation between the pressure change ratio inside a train and the pressure difference of inside and outside of the train.

• Journal of the Korea Institute of Building Construction
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• v.19 no.3
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• pp.229-237
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• 2019

This study examines the estimation of strength through a ultra-high strength concrete mock-up specimen using the rock compressive strength test hammer. According to the test result, the commonly used strength estimation formulae showed differences among them when the data of this test were applied. In additional, it show that these formulae underestimated the actual measurements further when the compressive strength was 30MPa or greater and deviated the distribution range of actual measurements in all strength ranges. The rock test hammer showed a higher correlation than type N Schmidt hammer regardless of the direction of hit for each type of W/B and the inclusion of coarse aggregate, and mortar showed a little higher correlation than concrete. As a result, it can be suggested that the coefficient of variation and the standard deviation of the mortar(2.26%/1.36) are lower than those of the concrete(4.06%/2.5), and the smaller the size of the coarse aggregate, the smaller the coefficient of variation and the more accurate the value.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.789-796
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• 2009

The randomness in the strength of a RC member is caused mainly by the variability of the mechanical properties of concrete and steel, the dimensions of concrete cross sections, and the placement of reinforcing bars and so on . Among those variations, the randomness and uncertainty of mechanical properties of concrete, such as compressive strength, tensile strength, and elastic modulus give the most significant influences and show relatively large statistical variations. In Korea, there has been little effort for the construction of its own statistical models for mechanical properties of concrete and steel, thus the foreign data have been utilized till now. In this paper, variability of compressive strength, tensile strength and elastic modulus of normal-weight structural concrete with various specified design compressive strength levels are examined based on the data obtained from a number of published and unpublished sources in this country and additional laboratory tests done by the authors. The inherent probabilistic models for compressive and tensile strength of normal-weight concrete are proposed as Gaussian distribution. Also, the relationships between compressive and splitting tensile strength and between compressive strength and elastic modulus in current KCI Code are verified and new ones are suggested based on local data.

• Journal of Korean Society of Disaster and Security
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• v.6 no.2
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• pp.23-30
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• 2013

A dynamic analysis of random vibration processes is concerned with the first excursion probability based on first passage time during some specified lifetime or duration of the excitation. This study is concerned with the estimation of first-passage probability for hazard fluctuate wind velocity in the major cities reflecting the recent meteorological with largest data samples (yearly 2003-2012). The basic wind speeds were standardized homogeneously to the surface roughness category C, and to 10m above the ground surface. In this paper, the hazard fluctuate wind velocities are treated as a time-independent (stationary) random process and Gaussian random processes. The first excursion probability were calculated from Poisson model based on the independent event of level crossing & two-state Markov model based on the envelopes of level crossing.

• Journal of the Korean Wood Science and Technology
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• v.33 no.1 s.129
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• pp.21-28
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• 2005

Tracheid length and width, microfibril angle, compressive, bending, and impact strengths between the south and north sides of stem pith in Larix kaemferi were measured. Sample trees were 30 years old which had planted in the central region of Korea. In general, there were no difference in the tracheid length and width, microfibril angle, and strengths between the two sides. And no difference in tangential shrinkage and strengths between the two sides was thought to be due to identical microfibril angle between the two sides.

• Journal of the Earthquake Engineering Society of Korea
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• v.5 no.2
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• pp.73-82
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• 2001

본 연구는 실험적 방법과 해석적 방법을 통하여 반복하중을 받는 ├형 철근콘크리트 접합부의 전단특성을 파악함을 목적으로 한다. ├형 접합부는 고강도 재료의 사용으로 인한 체적의 감소 뿐만 아니라, 지진발생 시 반복하중의 작용으로 인한 변동축력 등으로 , 구조적으로 취약한 부분이 될 가능성이 있다. 따라서 본 연구에서는 ├형 접합부의 전단특성을 파악하기 위하여 기동축력, 콘크리트 압축강도, 접합부 전단보강근비를 변수로 한 12개의 실험체를 제작하여 가력실험을 수행하였다. 또한, 유한요소 해석을 수행하여 본 실험결과와의 비교 검토를 통하여 타당성을 검토한 후, 기둥축력과 콘크리트 압축강도의 변화에 대한 변수해석을 통하여 접합부의 전단강도에 미치는 변수는 영향을 파악하였으며, 실험에 의한 실험체의 전단내력을 기존에 제안된 AIJ, ACI 규준 등과 비교 검토하였다. 본 연구의 결로부터 기둥축력과 콘크리트 압축강도가 ├형 철근콘크리트 접합부의 전단강도에 미치는 영향을 확인하였다.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.421-430
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• 2011

As a fundamental study to introduce the reliability-based design code, a statistical study is conducted for the material strength data collected from domestic construction sites. In order to develop a rational design code based on statistics and reliability theory, it is essential to obtain the statistical properties of material strength. Material strength data for concrete, reinforcing bars, and prestressing strands which are used in domestic construction sites are collected and statistically analyzed. Then, the statistical properties are compared with those used in the process of the reliability-based calibration of internationally leading design codes. The statistical properties of the domestic data are such that the bias factor is relatively uniform between 1.13 and 1.20 and the coefficient of variation is below 0.10. Reinforcing bar data show difference among different manufacturers but there is not much difference among re-bar diameters. In the case of tendons, which are high strength materials, both of the domestic and foreign data show smaller values of the bias factor and the coefficient of variation than those of concrete and re-bar. Statistical distribution of all the material strength can be properly assumed as normal, log-normal, or Gumbel distribution after analyzing the classified data by individual construction site and manufacturer rather than the mixed data obtained from different sources in order to express the individual distribution of each structure.

• The Korean Journal of Financial Management
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• v.16 no.2
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• pp.337-364
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• 1999

본 연구에서는 국내 주가지수선물시장과 현물시상간의 일중 가격 및 가격변동성의 선-후행관계를 실증적으로 분석함으로써 양 시장간의 동적관련성을 살펴보고자 하였다. 먼저, 상관관계분석의 결과는 KOSPI 200 주가지수선물수익률과 현물수익률, 그리고 주가지수선물수익률자승과 현물수익률 자승간에 유의한 교차상관관계가 존재하는 것으로 나타났다. 수익률의 선-후행관계를 살펴보기 위한 주가지수선물수익률의 시차변수들과 현물수익률간의 다중회귀분석의 결과는 주가지수선물수익률이 현물수익률을 약 15분 정도 선행하는 것으로 나타났으며, 이러한 현상은 현물수익률에 존재할 수 있는 비동시적 거래의 영향을 통제한 경우에도 비록 그 강도가 약하기는 하지만 여전하였다. 다음으로, 수익률 변동성의 선-후행관계를 살펴보기 위해 Grammatikos-Saunders (1986)가 제시한 무조건부 변동성의 추정치인 로그수익률자승을 사용하여 분석한 결과 주가지수선물수익률의 변동성이 현물수익률의 변동성을 약 10분 정도 선행하는 것으로 나타났으며, 이러한 결과는 비동시적 거래의 영향을 통제한 경우에도 동일하였다. 또한, Nelson(1991)의 EGARCH모형을 사용하여 수익률의 변동성을 추정한 후 이를 갖고 분석한 결과, 특히 비동시적 거래의 영향을 통제한 경우에는 주가지수선물시장과 현물시장의 수익률 변동성간에 선-후행관계가 존재한다는 것을 부정할 수 없었다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.26 no.1
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• pp.51-56
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• 1990

The authors carried out an experiment to investigate the echo fluctuations from ocean bottom due to ship's motion. The bottom echoes was continuously measured, by using a 50 kHz Echo sounder on board of the ship being at anchor under the sea condition of 15 knots in wind velocity and approximately 2 meters in wave height, to extract the information about the pulse stretching and the ship's motion from the first return and the second return. A data acquisition system was used to record digitally the envelope of the echoes, and the analysis was applied to the echo data collected from the continental shelf in the South China Sea. The results obtained can be summarized as follows: 1. The equivalent pulse width of the second return echoes from ocean bottom was 2.4 times longer than that of the first return echoes. 2. The echo peak values of the first return fluctuated markedly than that of the second return and was shown to be extremely sensitive to small change in ship's motion. 3. Energy target strength and peak target strength of the sandy-mud bottom were -13.4 dB and -14.6 dB, respectively.