• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.1
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• pp.41-51
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• 2018

In case of evaluating the bond stress of a void deck plate using a wire steel, there is no standard formula considering both the influence on the void and the type of the reinforcing bar. Therefore we proposed a model equation considered the bond characteristics of the void deck plate. A total of 46 specimens was carried out a direct pull-out test and the test variables were the presence of a void body, type of reinforcing bar, the inner cover thickness according to the location of reinforcing bars and bond region. As a result of the comparison between the steel bar and steel wire, the bond stress of the steel wire with the relative rib area of 0.071 is 4.5 ~ 28.58% lower than that of the steel bar with 0.092 and the bond stress reduction rate increases when the inner cover thickness is insufficient. In the case of the inner cover thickness of $1.7d_b$ and $2.7d_b$, the bond stress was reduced to 48.7 ~ 68.4%. In the inner cover thickness was $4.9d_b$ and $5.2d_b$, the bond stresses were equivalent to those of the solid specimens. It was confirmed that the average bond stress and strain were affected by the inner cover thickness. Therefore the predicted model for one module of the void deck plate is proposed and verified by considering the bond characteristics of the void deck plate.

• Journal of the Korea Concrete Institute
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• v.25 no.2
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• pp.155-163
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• 2013

This study investigated the bond characteristics of embedded deformed steel bar in donut type biaxial hollow slabs. The donut type hollow sphere make concrete inner cover formed between steel bar and hollow sphere due to the hollow shape and arrangement. Generally, inner cover was thinner than outer cover, and some part of donut type biaxial hollow slab has smaller inner cover thickness than $2.5d_b$. It was affected to the bond condition of deformed bar. Furthermore, inner cover thickness changes along the longitudinal deformed bar due to hollow shape. Therefore, donut type hollow slab was divided 3 regions according to the hollow shape such as insufficient region, transition region, sufficient region. Pull-out test were performed to find out the effect of bond condition by the region. Main parameters are inner cover thickness, embedded length and bond location. Bond characteristics of donut type biaxial hollow slab were confirmed through comparison of bond stress-slip relationship, maximum bond strength and bond stress distribution of each regions. And the calculation method of bond strength of donut type biaxial hollow slab was suggested based on the test results.

• KIEAE Journal
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• v.10 no.3
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• pp.11-16
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• 2010

This paper has attempted to investigate the change in soil moisture volume and temperature of architecture by planting ground(soil thickness and soil mixture ratio) and ground cover plants(Sedum sarmentosum, Zoysia japonica, Chrysanthemum zawadskii) for middle region green roof system. For this, a test was conducted on the roof of Konkuk University building from April 2009 to October 2009. In terms of treatment, five types(SL, $P_7P_1L_2$, $P_6P_2L_2$, $P_5P_3L_2$, $P_4P_4L_2$) depending on soil mixture ratio and two types(15cm, 25cm) by soil depth were created. Results of soil moisture volume by soil mixture ratio in the 15cm soil thickness showed that the difference was significance between simple soil and mixture soil treatment, however, the statistical significance was not recognized according to soil mixture ratio. In case of 25cm soil thickness, soil moisture volume by soil mixture ratio was more higher 7Vol.%~10Vol.% in the mixture soil than simple soil treatment. In terms of districts planted ground cover plants, soil volume moisture differed among plants in the order Zoysia japonica 17.74 Vol.%$34.86^{\circ}C$, district non-planted $27.49^{\circ}C$, Sedum sarmentosum $25.11^{\circ}C$, Chrysanthemum zawadskii $23.08^{\circ}C$, Zoysia japonica $24.45^{\circ}C$ respectively So, concrete surface showed more higher $5^{\circ}C{\sim}15^{\circ}C$ than other things among the all the time. Result of inner temperature of the architecture and soil, it was measured inner of architecture $25.69^{\circ}C$, inner district non-planted $24.29^{\circ}C$, Chrysanthemum zawadskii $23.90^{\circ}C$, Zoysia japonica $24.02^{\circ}C$, Sedum sarmentosum $25.13^{\circ}C$, respectively.

• Design & Manufacturing
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• v.12 no.1
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• pp.52-57
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• 2018

With the recent strengthening of environmental regulations and the need for cost reduction, excavators, a type of construction equipment, are being miniaturized while components are being developed in consideration of stability. In the case of excavator press parts, mainly high-strength steel sheets are being used to enhance stability and reduce weight. However, in the case of high-strength materials, there is a need to research product forming methods to reduce Springback in defects arising in parts assembly due to Springback that result from the internal residual stress that occurs in press forming being released after product forming. Accordingly, regarding the tank cover, an excavator press-forming part, this study selected a method to reduce distortion through analysis of the Springback occurrence rate and Springback causes through a forming analysis. A forming analysis was conducted for the Springback of the tank cover. Deformations of 13.714 mm in the upper part and 6.244 mm in the inner part of the product occurred, while wrinkles occurred on the sides of the product due to uneven thickness. A forming analysis was conducted for the major shapes of the product to investigate the causes of Springback. Distortion deformation due to the bead in the center of the product was confirmed to be a large factor. A Springback reduction method of correcting uneven thickness in the product sides, a Springback reduction method of removing the bead, and a correction method of restriking after the final forming were used in a forming analysis to determine the degree of Springback reduction. For the forming method to correct uneven thickness in the sides, deformation was reduced by 12% in the upper side compared to the existing model, but deformation in the inner side increased by 1%. For the restriking forming method, deformation decreased by 25% in the upper side and 13% in the inner side. For the bead removal method, deformation decreased by 28% in the upper side and 13% in the inner side, the largest Springback correction results. This indicates that the bead has a large affect on Springback.

• Corrosion Science and Technology
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• v.13 no.1
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• pp.20-27
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• 2014

The structures of reinforced concrete has been extensively increased with rapid development of industrial society. Futhermore, these reinforced concretes are easy to expose to severe corrosive environments such as sea water, contaminated water, acid rain and seashore etc.. Thus, corrosion problem of inner steel bar embedded in concrete is very important in terms of safety and economical point of view. In this study, multiple mortar test specimen(W/C:0.4) with six types having different cover thickness each other was prepared and was immerged in seawater solution for five years to evaluate the effect of cover thickness and immersion years to corrosion property of embedded steel bar. And the polarization characteristics of these embedded steel bars was investigated using electrochemical methods such as measuring corrosion potential, cathodic polarization curve, and cyclic voltammogram. At the beginning of immersion, the corrosion potentials exhibited increasingly nobler values with increasing cover thickness. However, after immersed for 5 years, the thicker cover of thickness, the corrosion potentials shifted in the negative direction, and the relationship between corrosion potential and cover thickness was not in good agreement with each other. Therefore, it is considered that the thinner cover of thickness, corrosive products deposited on the surface of the embedded steel bar plays the role as a resistance polarization which is resulted in decreasing the corrosion rate as well as shifting the corrosion potential in the positive direction. As a result, it seemed that the evaluation which corrosion possibility of the reinforced steel would be estimated by only measuring the corrosion potential may not be a completely desirable method. Therefore, it is suggested that we should take into account various parameters, including cover thickness, passed aged years as well as corrosion potential for more accurate assessment of corrosion possibility of reinforced steel which is exposed to partially or fully in marine environment for long years.

• Journal of Korea Technical Association of The Pulp and Paper Industry
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• v.42 no.3
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• pp.28-36
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• 2010

Today We have three full series of the annals of Joseon Dynasty. Taebaeksan volume which is one of them shows comparatively good maintenance but Taebaeksan volume also decomposed in patches. The size of cover and inner paper were increased in late Joseon Dynasty, but the weight, thickness and basis weight bears no relation to each other. The oxidation index of paper in annals of pre-periods of King Sunjo shows very high value. After the annals of King Sunjo, the oxidation index of paper is very similar to today's Hanji. L.a.b values of inner paper in the Taebaeksan volume are similar generally. The average length of fiber using image analysis soft ware is 8.08~9.92 mm, that like immediate value of measurement. The air fraction of fiber's range is 1.20~2.12%. It lower than today's Hanji. After considering the factors of the length of fiber, air fraction and FE-SEM, we reached that no difference between raw material of inner paper in the Taebaeksan volume.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.7
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• pp.994-1002
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• 2009

In this paper, effect of air gap thickness between absorber plate and glass cover on top heat loss of a closed loop oscillating heat pipe (CLOHP) solar collector was investigated. The CLOHP, which is made of copper with outer diameter of 3.2mm and inner diameter of 2.0mm, comprises 8 turns with heating, adiabatic and cooling section. The heating section of the heat pipe was attached to absorber plate which heated by solar simulator simulated by halogen lamps. The cooling section of the heat pipe was inserted into collector's cooling section that made of transparent acrylic. Temperatures of absorber plate, glass cover, and ambient air measured by K-type thermocouple and were recorded by MV2000-Yokogawa recorder. Top heat loss coefficients and top heat loss of the collector corresponding to some cases of air gap thickness were determined. The result of experiment shows the optimal air gap thickness for minimum top heat loss of this solar collector.

• Journal of Ocean Engineering and Technology
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• v.30 no.4
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• pp.327-333
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• 2016

Reinforced concrete structures have found wide usage in land and maritime applications. However, the corrosion of reinforced concrete has been recognized as a serious problem from economic and safety standpoints. In previous studies, the corrosion behavior of the inner steel bar embedded in mortar (W/C: 0.4, 0.5) was investigated using electrochemical methods. In this study, multiple mortar test specimens (W/C: 0.6) with six different cover thicknesses were prepared and immersed in flowing seawater for five years. Subsequently, equations related to the cover thickness, period of immersion, and corrosion characteristics of the embedded steel bar were evaluated using electrochemical methods. Prior to immersion, the corrosion potentials indicated an increase with increasing cover thickness, and after five years, all corrosion potentials demonstrated a trend in the positive direction irrespective of the cover thickness. However, the relationships between the corrosion potential and cover thickness were not in complete agreement. Furthermore, after five years, all of the corrosion potentials indicated values that were nobler compared to those obtained prior to immersion, and their corrosion current densities also decreased compared to their values obtained prior to immersion. It was considered that the embedded steel bar was easily corroded because of the aggression of water, dissolved oxygen, and chloride ions; a higher W/C ratio also assisted the corrosion process. The corrosive products deposited on the surface of the steel bar for five years cast a resistance polarizing effect shifting the corrosion potential in the nobler direction. Consequently, it was considered that the W/C ratio of 0.6 showed nearly same results as those of W/C of 0.4 and 0.5. Therefore, the corrosion potential as well as various parameters such as the cover thickness, period of immersion, and W/C ratio must be considered at once for a more accurate evaluation of the corrosion property of reinforced steel exposed to marine environment for a long period.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.543-546
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• 2002

This paper discussed micro - structure of skin concrete to understand transport properties from surface and seek thickness from surface which is seriously influenced on durability. Concrete at nearer surface has high porosity relative to inner concrete. The porosity of concrete and ISAT value at region from surface to 20 mm depth is decreased with depth. On the other hand, according to the result of ASTM C 1202 with specimen thickness, critical depth which affects fast ionic penetration through interfacial transition zone (ITZ) equals 35mm and the critical depth would be directly influenced by the effects of ITZ on chloride diffusion unrelated with W/C ratio.

• Journal of the Korean Institute of Gas
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• v.21 no.3
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• pp.39-45
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• 2017

The LNG storage tank as core facility of LNG industry is mainly composed of the inner tank of nikel 9% steel and the outer tank of prestressed concrete. To respond proactively increased risk of structure performance deterioration due to fatigue of the inner tank and durability reduction of the outer tank, life evaluation program for LNG storage tank is needed. In this study, life evaluation program for LNG storage tank was developed to assess fatigue of the inner tank and durability(carbonation and chloride attack) of the outer tank. By defining the main three scenarios in the inner tank, the fatigue life analysis is conducted from structural analysis and Miner's damage rule. Carbonation progress of the outer tank is predicted according to thickness of cover concrete by using carbon dioxide contents and data of penetration depth. To consider a variety of input conditions and a reliability in results of chloride attack, the evaluation of choride attack for the outer tank is constructed through Life-365 program of open source.