• Journal of the Korea Computer Industry Society
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• v.9 no.3
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• pp.137-142
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• 2008

The major influence factor on chloride penetration into concrete structures is chloride ion concentration. In this study, chloride penetration analyses with chloride ion concentration were carried out by the developed program. Also, the service life of concrete structures was predicted. The penetration depth was 32mm in case that chloride ion concentration wad 600ppm. It was shown that the service life of concrete structures with 40mm cover depth was 167 years even though they had been exposed at chloride ion concentration 600ppm during 100 years.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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• pp.163-166
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• 2006

The purpose of the research is to assess the accuracy of steel bar detector among other nondestructive testing equipment. The result of previous research shows that the average errors of rebar detector are 14.7% for the cover depth, 2.3% for the rebar spacing, and 11% for the rebar diameter. But this experiment was performed at the laboratory and the mortar was used for covering the steel bars instead of concrete. In situ condition can be different from the laboratory's so the outcomes do not correspond with those of laboratory. This research was performed at the buildings to be reconstructed. Nondestructive and destructive testing can be performed side by side since the building if to be destroyed. Steel bar detector was operated on the beam and the column and concrete cover of those members was removed for the actual measurement of rebar depth, spacing, and diameter finally, presumed value can be directly compared with actual data.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.10a
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• pp.108-108
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• 2009

가전분야에서 EG강판 위에 피복된 크롬－프리 코팅은 내식성 및 심미성 이외에도 전기전도성이 요구되는데 이는 가전기기로 사용되므로 전자파 차폐성 및 용접성을 부여하기 위함이다. 내식성의 관점에서 보면 코팅된 수지 부착량이 많을수록 부식인자의 침투를 방해하여 내식성이 향상되나 일정한 부착량 이상에서는 전기전도성이 취약해지는 단점을 가지게 된다. 따라서 본 연구에서는 수지내에 나노금속분말을 고르게 분산시키는 연구 및 이를 이용하여 기존의 수지두께 이상에서도 전기전도성을 가질 수 있는 강판을 연구하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.4
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• pp.181-188
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• 2002

The objective of this study is to determine crack depth located under steel reinforcement in concrete specimens using ultrasonic method. Experimental studies were performed on concrete specimens containing vertical and inclined surface-opening cracks with known depths. The other studies were carried out on specimens with flexural crack. Experimental results have shown that the crack depth is effectually measured when the distance between the probes is less than the crack depth. The effect of steel on crack depth estimation is studied through a model by considering P-waves diffaction at the tip of crack and steel. In addition, experimental results show that the ultrasonic method is one of useful methods to evaluate the crack depth in reinforced concrete.

• Journal of Bio-Environment Control
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• v.9 no.3
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• pp.156-160
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• 2000

The Plasma film treated with a high electric voltage was developed to enhance flow down of condensation drops on inside plastic film. Arch type greenhouse framed with iron pipe of 25mm diameter defand 1.5mm thickness were covered with either the developed plasma film or surfactant film(control). Green pepper seedlings raised for 40 days in plug trays were transplanted at a density of 110cm by 30cm in each greenhouse. The mount of condensational water on film surface, generated by 7$0^{\circ}C$ water bath chimney systems and flew down, was collected and measured. The amount of collected water after 150 minutes was 2.56 mL.100c $m^{-2}$ and 0.94mL.100c $m^{-2}$ , respectively, in the plasma film and surfactant film-covered greenhouses. The amount of condensational water drops attached on the cover at 08:20 a.m. at 60 days filter covering was 0.34mL.100c $m^{02}$ and 0.32mL.100c $m^{-2}$ , respectively, in the plasma film- and surfactant film-covered greenhouses. Solar irradiance transmitted into greenhouse was 2.0% higher in the greenhouse covered with the plasma film tan that in the greenhouse covered with the surfactant film. Air temperature in the plasma film-covered greenhouse was higher than the surfactant film-covered greenhouse by 0.5$^{\circ}C$. However, there was no difference in relative humidity between the two greenhouse. Plant height, leaf area, dry weight and early yield showed no significant differences.s.

• Current Research on Agriculture and Life Sciences
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• v.24
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• pp.23-27
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• 2006

Seedling characteristics of rice on nursery covered with different weight of polypropylene spunbonded fabric(PSF) were investigated to determine the optimum thickness of PSF for raising of healthy rice seedlings. Four different thickness of PSF 40, 60, 80 and $100g/m^2$ were used in the seedling nursery with a conventional polyethylene(PE) film. PSF and PE were taken off in 20 days after sowing(DAS) on April and in 10 DAS on June. Plant height of 20- and 30- day old seedlings in PSF covering nursery was slightly taller as the increase of PSF thickness from $40g/m^2$ to $100g/m^2$, but number of leaves and shoot dry-weight of the seedlings was reduced. Root solidity of seedlings grown in lighter PSF ($40{\sim}60g/m^2$) covering nursery was more favorable than that in relatively heavier PSF($80{\sim}100g/m^2$). The optimum thickness of PSF for the raising of healthy seedlings was $40{\sim}60g/m^2$ PSF at sowing on April 20 and April 30 for single cropping, and $40g/m^2$ PSF on June for double cropping based on the growth characteristics of seedlings investigated at seedling nursery covered with different thickness of PSF.

• Journal of the Korea Concrete Institute
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• v.16 no.3 s.81
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• pp.293-302
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• 2004

The transfer of prestress force in pretensioned prestressed concrete (PSC) members is of great concern because it affects directly the distribution of stress around the transfer zone. The design provision of current design code on the transfer length considers only the prestress intensity and the diameter of prestressing steels. However, other factors such as concrete compressive strength and concrete cover may affect greatly the transfer length. The purpose of the present paper is to explore the various factors that affect the transfer length in pretensioned PSC members. The bond stress-slip relation between prestressing steel and concrete was modeled first from experimental data and then this model was incorporated into the interface element. The interface element was used to perform the finite element analysis for pretensioned PSC members. The results indicate that the compressive strength and concrete cover are also very important parameters which affect the transfer length greatly. This means that the current design code, which considers only the effective prestress and diameter of prestressing steel, must be improved to take into account the other important variables of compressive strength and concrete cover. The present study allows more realistic analysis and design of pretensioned PSC members.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.285-288
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• 2008

A model for the effective moment of inertia $I_{\epsilon}$ as expressed in Branson's equation, in which reduction of the flexural rigidity of RC beams due to cracking are aptly taken into accoun,t is presented. However, KCI Code isn`t considered tension stiffening as it is in debonding of reinforcing bar. Therefore, this equation need to set up suitable to our design Code. The experimental work consisted of casting and testing a total of 6 simply supported reinforced concrete beams and a total of 4 continuos reinforced concrete beams under two point concentrated loads. Main parameters are concrete strength, coverage, bond between concrete and reinforcing bars, are known as have an effect on deflection and tension stiffening. Every test beams had the same $250{\times}350$mm rectangular section, with a simply supported clear span of 4,400 mm and a continuos clear span of 6,500 mm. Comparison of the test results with values obtained using the KCI Code equation of the effective moment of inertia showed a noticeable difference.

• Journal of the Korea Concrete Institute
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• v.19 no.3
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• pp.323-331
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• 2007

The development length equations of the GFRP rebars are suggested based on the pullout tests performed in this study. A total of 48 pullout and modified pullout tests were completed. Test variables included embedment length (L=10, 15, 20, and $30d_b$), vertical and horizontal installation of the rebars, height of the rebars (H=100 and 300 mm), and cover thickness $(C=2{\sim}5d_b)$. D13 GFRP rebars domestically developed were used in the experimental program. The average of the bond strength of all vertically installed GFRP rebars was 6.39 MPa with a 5% fractile of 4.63 MPa. A basic development length equation was derived that resulted in an equation equivalent to the one proposed in the ACI 440.1R-03. Careful reevaluation of the bond strength using the modified pullout test indicated that a modification of the design equation was necessary so that the basic development length increases by 11%. The top bar effect of the horizontally installed rebars as well as the effect of the cover thickness were determined and included in the set of suggested equations. Since the current equations were derived from testing rebars embedded in relatively low strength concrete $(f_{ck}=20{\sim}24MPa)$, they result in conservative development lengths when applied to bars embedded in higher strength concretes.

• Fire Science and Engineering
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• v.25 no.6
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• pp.89-97
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• 2011

This study is for evaluating the fire resistance performance (1~2 h) of the RC Structure void slab using the Lightweight Hollow Sphere, which can reduce the unnecessary dynamic part of removing the central concrete. For this experiment, we set up depth of concrete cover, live load, and span length as the factors. The result comes out with all the slabs under those conditions can ensure the goal fire resistance performance (120 min). And among these factors, the resisting capability changes more sensitively with the live load rather than the thickness of cover. And the shorter span length could assure the better the fire resistance performance. The result observing the character in high temperature of the Lightweight Hollow Sphere which does not used as existing RC structure slab, a delay section in temperature change is occurred due to the Glass Transition in $100^{\circ}C$. And heat transfer by conduction does not occur at lightweight hollow sphere because the polystyrene in EPS (Expanded Polystyrene) melts point in $185^{\circ}C$. Therefore temperature at lightweight hollow sphere is lower than the concrete and rebar.