• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.5
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• pp.119-126
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• 2018

Recently, the production of circulating fluidized bed combustion ash has been increased in thermal power plants. The addition of limestone for the desulfurizing effect of circulating fluidized bed boiler ash increases the content of CaO and $SO_3$ contained in ash, which is higher than the free fly ash in general fly ash. Unlike conventional fly ash, the circulating fluidized bed combustion ash has a high reactivity when it comes into contact with water due to its hydraulic properties and high free-CaO content. The aim of this study is to investigate the possibility of non-sintered binder by using self-cementing properties of circulating fluidized bed combustion ash. The mechanical and hydration characteristics were investigated according to the content of CFBC ash. In addition, the effects of gymsum type and content on the compressive strength and micro-structure of non-sintered binder pastes.

• Journal of the Korean GEO-environmental Society
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• v.14 no.5
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• pp.23-32
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• 2013

This paper presents the effect of pile diameter on the lateral behavior of offshore pile for wind turbine. The material parameters of the soils were estimated through SPT on the Southwestern offshore area in Korea, where the first wind farm is planned. The FDM software, FLAC3D, and LPile were adopted to derive the load-displacement curve, p-y curve, and maximum bending moment at a specified displacement. It was found that the results from softwares significantly differ and the LPile could overestimate the allowable capacity. The maximum bending moment along the pile with 2m diameter could be as large as four times the bending moment with 1m diameter. Similar trend was observed for the allowable lateral capacity.

• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.46-52
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• 2015

Pump-turbine system is widely used by the hydropower industry for stabilizing the electrical grid in the vast growing economy of most developed countries. This study only investigates the Fluid-structure Interaction (FSI) analysis of the pump-turbine system at various operating conditions. The FSI analysis can show how reliable each component of the system is by providing the engineer with a better understanding of high stress and deformation points, which could reduce the lifespan of the pump-turbine. Pump-turbine components are categorized in two parts, pressurized static parts and movable stressed parts. The fixed parts include the spiral casing, top and bottom cover, stay vane and draft tube. The movable parts include guide vanes and impeller blades. Fine hexahedral numerical grids were used for CFD calculation and fine tetrahedral grids were used for structural analysis with imported load solution mapping greater than 90 %. The maximum equivalent stress are much smaller than the material yield stress, and the maximum equivalent stress showed an increasing tendency with the varying of operating conditions from partial to excessive at both modes. In addition, the total deformation of all the operating conditions showed a small magnitude, which have quite small influence on the structural stability. It can be conjectured that this system can be safely implemented.

• Journal of the Korean Solar Energy Society
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• v.35 no.4
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• pp.25-34
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• 2015

This research is carried out to provide fundamental data for the design of solar photovoltaic systems. Methodologically, the solar radiation installations from 10 different pyreheliometers are measured, which are set up at 6 and 4 different levels of tilts and azimuth, respectively. Maximum of a yearly accumulated solar radiation is $1,569.8kWh/m^2{\cdot}year$ with a tilt angle of $30^{\circ}$ and an azimuth angle of $0^{\circ}$(south), $1,558.5kWh/m^2{\cdot}year$ with an azimuth angle of $0^{\circ}$(south) in combination of a tilt angle of $35^{\circ}$. This paper estimates that in designing fixed solar photovoltaic systems with a tilt angle of $12.5^{\circ}{\sim}50^{\circ}$(south) and a tilt angle of $35^{\circ}$ in combination of an azimuth angle of $S45^{\circ}W{\sim}S45^{\circ}E$, a tilt angle and an azimuth angle will cause a maximum 6.8% and 9.9% of efficiency variation respectively, depending on a installed solar module's angle and direction.

• Journal of the Korean GEO-environmental Society
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• v.2 no.1
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• pp.67-79
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• 2001

The objective of this study is to determine the engineering properties of micro fine hybrid silicate grout materials that were developed recently. In this study, MSG-N type was mainly used as grout materials, and the chemical components, grain size distribution, mineral characteristics were analyzed. Moreover, the properties of active silica and ordinary portland cement acting as coagulating agent were analyzed and compared with each other. To determine the engineering properties, the bleeding test, viscosity test, coagulation test, examination with naked eye, photographing by using SEM, uniaxial compression test and in-situ application test for reclaimed ground were carried out. A series of test results showed that the strength of micro fine hybrid silicate grout materials was about twice that of ordinary sodium silicate grout materials, and alkali leakage decreased dramatically when MSG method was utilized. Especially, based on the evaluation of the application of the MSG method to field, this method would be very effective in reducing coefficient of permeability due to its excelent permeability.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.176-181
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• 2018

Concrete structures are degraded physically and chemically due to various reasons after construction. Because the deterioration of concrete structure reduces the service life, reasonable repair and maintenance techniques are needed. Recently, in order to efficiently repair concrete structures, many researches on hybrid repair materials having improved adhesion performance have been carried out actively. In this study, we developed a hybrid repair material containing rapid hardening cement, PVA powder, nylon fiber, and latex to improve adhesion and water-tightness of existing concrete. The compressive strength, drying shrinkage and the adhesion strength test were carried out to evaluate the performance of the repair material. In addition, the flexure bond performance was evaluated before and after repair. From the results, the bending strength was 110% ~ 150% in all specimens except for the specimen containing only the rapid hardening cement, and all the specimens behaved with the existing concrete in the crack pattern generated by the bending strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.123-129
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• 2018

Recently, there has been a growing interest in the study of treatment of $CO_2$ generated by industrial activities and resource recycling of industrial byproducts. The aim of this study is to investigate the applicability of industrial byproducts that can be used as concrete mixed materials by carbonation curing. For this purpose, the physical and chemical changes of the pastes with research cement(RC), blast furnace slag powder (GGBFS) and circulating fluidized bed combustion ashes (CFBC) were evaluated by carbonation curing. XRD and SEM analyzes were performed to investigate micro-structural changes. As a result, it was confirmed that calcium carbonate, which is a reaction product produced by carbonation curing, filled the space inside the paste and formed a dense micro-structure. Also, as the $CO_2$ curing time increased, it was confirmed that calcium carbonate crystals were grown together to form a dense micro-structure.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.182-188
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• 2018

Recently, various researches on the utilization of carbon nanotube(CNT) with superior electrical conductivity and large surface areas into concrete have been actively conducted. Thus, mechanical and thermal properties of cement-flyash composites were evaluated concerning the CNT replacements. Based on the low binder-to-water ratio, the cement composites were produced with 0.2 % and 0.5 % of CNT solids. The compressive strengths with various ages, isothermal calorimetry measurement, SEM analysis, thermal conductivity of cement composites and thermal gravimetry analysis were implemented. As the amount of CNT addition was increased, the thermal conductivity of cement composites were also increased. Also, there was no significant mechanical property differences between mixtures with and without CNTs.

• Journal of the Korean Society of Industry Convergence
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• v.3 no.4
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• pp.307-317
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• 2000

The purpose of this study is to form a calculation formula of the mean skin temperature on the human body in a heated room by the use of floor heating system. Korean traditional floor heating system is a long way from being defunct. The floor heating systems based on hot water have been coming into wide use mainly in the apartment house. However, it is considered that the design process and evaluation method for the floor heating systems in the standpoint of human being are not established so far. In the floor heating systems, air temperature as well as floor temperature should be considered as physical factors which affect the sensation of human body. Furthermore, extremely few studies have been performed on the sitting with legs crossed posture sedentary which is the typical dwelling life style of residents from the ancient times in Korea, while a large number of studies on the influence of the floor heating systems on the human body in standing and sitting on a chair sedentary have been carried out. Especially, it is essential to elucidate how mean skin temperature on the human body is affected by thermal conduction in the contact area between the sitting with legs crossed posture sedentary human body and floor including thermal radiation due to the combination of air temperature and floor temperature, but the studies dealt with such issues have hardly been performed. Based on the above statements, the influence of the environment condition due to the combination of air temperature and floor temperature is discussed in the present investigation through theoretical of mean skin temperature on the human body in the floor heating systems.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.4
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• pp.121-128
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• 2003

In recent years, various artificial neural network algorithms are used in the damage assessment of civil infrastructures. So far, many researchers have used the artificial neural network as a pattern classifier for the structural damage assessment but, in this paper, the neural network is used as a structural reanalysis tool not as a pattern classifier. For the model updating using the optimization algorithm, the summation of the absolute differences in the structural vibration modes between undamaged structures and damaged ones is considered as an objective function. The stiffness of structural components are treated as unknown parameters to be determined. The structural damage detection is achieved using model updating based on the optimization techniques which determine the estimated stiffness of components minimizing the objective function. For the verification of the proposed damage identification algorithm, it is numerically applied to a simply supported bridge model.