• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.353-364
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• 2011

In a previous research performed by the authors, the allowable compressive stress coefficient (K) in pretensioned members with rectangular section at transfer was proposed based on strength design theory. In this study, a subsequent research of an enormous analysis was performed to determine the K factor for Tee and inverted Tee section members, considering the effect of section height (h), section type, amount of tendons ($A_{ps}$), and eccentricity ratio (e/h). Based on the analysis results, the allowable compressive stress coefficients (K) for Tee and inverted Tee section members at transfer were derived, which limit the maximum allowable stresses as 80% and 70% of the compressive strengths at the time of release for Tee section and inverted Tee section, respectively. And these were larger than the allowable stresses specified in domestic and other international codes. In order to verify the proposed equations, they were compared to the test results available in literature and other codes, which showed that the allowable stresses in domestic and international codes are unconservative for the cases with low eccentricity ratios while conservative for those with high eccentricity ratios. The proposed equations, however, estimate the allowable stresses of the Tee and inverted Tee section members reasonably close to test results.

• Journal of the Korean earth science society
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• v.23 no.4
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• pp.349-356
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• 2002

In an effort to properly assess the validity of spaceborne radar altimeter measurements, we made a direct comparison of two different sea surface heights (SSH) acquired by both Topex/Poseidon (T/P) satellite and in-situ tide-gauges (T/G). This comparative analysis was conducted using the data sets collected from three locations along the eastern coast of Korea which include: Ulleungdo, Pohang, and Sokcho. In the course of the analysis of satellite altimeter, information of SSH was extracted from the T/P MGDR data sets through the application of both atmospheric and geophysical corrections. To compare the T/P data sets in parallel basis, the T/G data sets were averaged using the measured values within the peripheral radius of 55km. When compared among different locations, the compatibility between the two methods was much more significant in an offshore location (Ulleungdo) than the two onshore locations (Pohang, Sokcho). If the low-pass filtered results were compared among the sites, the offshore site exhibited the best correlations between the two methods (correlation coefficient of 0.91) than those of the onshore sites. These large differences in the strength of correlations among different locations are due to the deformation of M2, S2, and K1 tidal components used in the tidal model. In case of the offshore location, the compatibility of the two different methods were improved systematically by the low-pass filtering with an increase of the filtering duration such as up to 200 days.

• Journal of the Korean Recycled Construction Resources Institute
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• v.4 no.2
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• pp.149-156
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• 2016

It has been well known that concrete structures exposed to chloride and sulfate attack environments lead to significant deterioration in their durability due to chloride ion and sulfate ion attack. The purpose of this experimental research is to evaluate the long-term durability against chloride ion and sulfate attack of the alkali activated cementless concrete replacing the cement with ground granulated blast furnace slag. For this purpose, the cementless concrete specimens were made for water-binder ratios of 40%, 45%, and 50%, respectively and then this specimens were cured in the water of $20{\pm}3^{\circ}C$ and immersed in fresh water, 10% sodium sulfate solution for 28, 91, 182, and 365 days, respectively. To evaluate the long-term durability to chloride ion and sulfate attack for the cementless concrete specimens, the diffusion coefficient for chloride ion and compressive strength ratio, mass change ratio, and length change ratio were measured according to the NT BUILD 492 and JSTM C 7401, respectively. It was observed from the test results that the resistance against chloride ion and sulfate attack of the cemetntless concrete were comparatively largely increased than those of OPC concrete irrespective of water-binder ratio.

• Journal of the Korea Institute of Building Construction
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• v.20 no.1
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• pp.1-9
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• 2020

Chloride ion, which penetrates into the cement composites from the outside, generally diffuses by the concentration gradient. Chloride ions are adsorbed by the chemical reaction with cement hydrates. Recent studies have shown that anion exchange resin (AER) powder can effectively adsorb the chloride ion in the cement composites, and thus, the cement composites containing AER have a high chloride adsorption capacity and a good resistance for chloride penetration. In this study, the chloride adsorption ability of the AER powder was investigated under the conditions of distilled water and calcium hydroxide saturated solution to determine if the AER powder is less effective to increase the chloride adsorption ability after grinding process. The chloride adsorption ability of AER powder was compared with the previous research about the chloride adsorption of AER bead. In addition, the compressive strength, chloride diffusion coefficient (using NT Build 492 method), and the chloride profile of cement mortar substituted with AER powder were investigated. There was no decrease in the chloride adsorption capacity of AER powder but increase in the kinetic property for chloride adsorption after the grinding process. The AER powder could absorb the chloride ion in the mortar quickly, and showed better chloride ion adsorption ability than the cement hydrates.

• Women's Health Nursing
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• v.7 no.3
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• pp.393-406
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• 2001

The purpose of this study was to find out women's need and level of knowledge about episiotomy, pain and discomfort related to episiotomy on a cross-sectional survey design. The subjects were 102 postpartal women agreed on oral consent. 34 postpartal women admitted at obstetric ward of H university hospital, 34 postpartal women admitted at 2 Sanhujoriwons, and 34 women within one year afterbirth. They were selected in Seoul, Korea. Data were collected from July, 1 to September 30, 2000, by a structured questionnaire. The instrument used for this study was a questionaire consisted of 5 items of general characteristics, 12 items of obstetric characteristics, 10 items of level of knowledge (Chronbach $\alpha$ .8176), 8 items of need of education(Chronbach $\alpha$ .8836), 3 items of pain (Chronbach $\alpha$ .9252), and 3 items of discomfort (Chronbach $\alpha$ .8092). The data were analyzed by the SPSS/PC+ program using t-test, ANOVA and Scheffe test as a post hoc and Pearson Correlation Coefficient. The results of the study were as follows; 1. 63.2% of respondents had right answer on 6-8 items among 10 items. Only 4.4% of women got right answer on 10 items all. 2. The need of education was high(4.45%) on all items and the range of score was $4.25{\sim}4.64$. 3. The strength of pain was the highest within one week afterbirth(5.93/10) and became lower in 8-14 days afterbirth(2.55). And after 15days of postpartum, the pain level became to the lowest level(1.08). However, pain was delayed until more than one month afterbirth. 4. The level of discomfort was the highest one week afterbirth(6.88/10) and became lower in 8-14 days afterbirth(4.20). And after 15days of postpartum, the discomfort level became to the lowest level(2.47). Universally, the degree of discomfort was higher than pain. 5. There was a strong positive correlation between discomforts and pain ($r=.752^{**}$) and weak positive correlation between discomforts and the level of educational need($r=.308^*$). In conclusion, women have a right to choose whether she will have episiotomy or not according to her decision making based on the comprehensive knowledge of episiotomy before they get episiotomy with consent process and explanation in detail. Women health care providers like nurses have a responsibility to do conscious raising and empowerment for women so that they could lead themselves to choose given medical treatments for women's health and wellbeing and the quality of life in her life cycle.

• Journal of Ecology and Environment
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• v.29 no.6
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• pp.489-494
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• 2006

For the ecosystem conservation and the effective management of naturalized plant species on 261 uninhabited islands distributed in southern and western sea in Korea, we tested the interrelationship between the pattern of distribution and dispersal of the naturalized plant species and the factors of geographical environment of uninhabited islands such as island area, distance from mainland, latitude, longitude, human impacts and habitat diversity. Out of 261 uninhabited islands surveyed, 106 species of the naturalized plants occurred on 229 (87.7%) islands. The naturalized plant species per island averaged 4.6 (SD=4.07) species, and plant species number were higher in southern group (87 species) than in western group (64 species) of islands. Plant species occurred on more than 100 islands were three species : Rumex crispus L. (153 islands), Erigeron annuus Pers. (130 islands), and Conyza canadensis (L.) Cronquist (121 islands), the highest grade '5' of 'degree of naturalization'. The occurrence frequency of 106 naturalized plant species was significantly correlated with island area, distance to mainland, strength of human impacts, and latitude and longitude. Correlation coefficient (r=-0.330) between occurrence frequency and distance from mainland was higher than between occurrence frequency and island area (r=-0.182). The result of path analysis confirmed that plant species number was significantly affected by island area p=0.336) and distance from mainland (p=-0.490), but in this analysis the effect of human impacts on plant species number was very weak (p=0.003). On the basis of these results, strategies on the conservation of ecosystem and the management of naturalized plant species in the uninhabited islands of Korea were discussed.

• Korean Journal of Construction Engineering and Management
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• v.10 no.5
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• pp.123-134
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• 2009

Since 1970s, urethane waterproofing method is broadly used in rooftops, underground spaces, and sports stadium for its outstanding ultraviolet blockage, watertightness, and elasticity. However, development of slippage-resistance and endurance, improvement of function considering convenience and visually pleasing of users, urethane waterproofing method is necessary, since rooftops and underground spaces have slippage and external force risks. Therefore, many improved waterproofing methods are being developed and, recently, embo-thane waterproofing method, which applies embo-spray coating system, has been developed. This paper explains exposure, nonexposure, and floor-material of embo-thane waterproofing method, and then perform experimental study for comparison with urethane waterproofing method about tensile strength, coefficient of expansion, performance of bond, anti-abrasion, and slippage-resistance. In addition, the performance index was presented for the superiority of embo-thane waterproofing method compared to urethane by setting up evaluation criteria considering not only physical performance but also design side of embo-thane waterproofing method, and Value Analysis applying AHP. Also for an assessment considering uncertain result, Monte Carlo Simulation Method was used to operate reliability analysis through statistic approach method.

• The Journal of Engineering Geology
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• v.27 no.2
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• pp.153-164
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• 2017

The geological factors for causing ground subsidence are very diverse. It can be affected by any geological or extrinsic influences, and even within the same geological factor, the soil depression impact factor can be determined by different physical properties. As a result of reviewing a large number of papers and case histories, it can be seen that there are seven categories of ground subsidence factors. The depth and thickness of the overburden can affect the subsidence depending on the existence of the cavity, whereas the depth and orientation of the boundary between soil and rock are dominant factors in the ground composed of soil and rock. In case of soil layers, more various influencing factors exist such as type of soil, shear strength, relative density and degree of compaction, dry unit weight, water content, and liquid limit. The type of rock, distance from the main fracture and RQD can be influential factors in the bedrock. When approaching from the hydrogeological point of view, the rainfall intensity, the distance and the depth from the main channel, the coefficient of permeability and fluctuation of ground water level can influence to ground subsidence. It is also possible that the ground subsidence can be affected by external factors such as the depth of excavation and distance from the earth retaining wall, groundwater treatment methods at excavation work, and existence of artificial facilities such as sewer pipes. It is estimated that to evaluate the ground subsidence factor during the construction of underground structures in urban areas will be essential. It is expected that ground subsidence factors examined in this study will contribute for the reliable evaluation of the ground subsidence risk.

• Journal of Korean Society of Environmental Engineers
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• v.22 no.1
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• pp.83-89
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• 2000

Bentonite has been considered as a liner material to restrict the release of hazardous heavy metals from the landfill. The adsorption of copper onto a domestic bentonite was studied to provide the adsorption isotherm and the effect of solution chemistry and temperature. The copper adsorption was fitted well to a Freundlich isotherm, in which Freundlich constants and correlation coefficient were calculated to be $K_F=1.18$, n=1.65, and $r^2=0.97$, respectively. The distribution coefficients ($K_d$) for the adsorption of copper decreased with increasing initial copper concentration. The $K_d$ increased with increasing the pH of solution, and drastically increased at pH > 5.3 because of precipitation of most copper species. As the ion strength of $Na^+$ in solution increased the $K_d$ decreased, while it increased with increasing the concentration of $SO_4{^{2-}}$ in solution. An increase in the temperature of experimental solution decreased the $K_d$ values.

• Korean Journal of Materials Research
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• v.18 no.10
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• pp.547-551
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• 2008

Crack-free joining of $Si_3N_4\;and\;Al_2O_3$ using 15 layers has been achieved by a unique approach introducing Sialon polytypoids as a functionally graded materials (FGMs) bonding layer. In the past, hot press sintering of multilayered FGMs with 20 layers of thickness $500{\mu}m$ each has been fabricated successfully. In this study, the number of layers for FGM was reduced to 15 layers from 20 layers for optimization. For fabrication, model was hot pressed at 38 MPa while heating up to $1700^{\circ}$, and it was cooled at $2^{\circ}$/min to minimize residual stress during sintering. Initially, FGM with 15 layers had cracks near 90 wt.% 12H / 10 wt.% $Al_2O_3$ and 90 wt.% 12H/10 wt.% $Si_3N_4$ layers. To solve this problem, FEM (finite element method) program based on the maximum tensile stress theory was applied to design optimized FGM layers of crack free joint. The sample is 3-dimensional cylindrical shape where this has been transformed to 2-dimensional axisymmetric mode. Based on the simulation, crack-free FGM sample was obtained by designing axial, hoop and radial stresses less than tensile strength values across all the layers of FGM. Therefore, we were able to predict and prevent the damage by calculating its thermal stress using its elastic modulus and coefficient of thermal expansion. Such analyses are especially useful for FGM samples where the residual stresses are very difficult to measure experimentally.