• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.110-116
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• 2013

A concrete structure has become bigger and higher because of development of construction technology and a change in construction environment. Also it tends to focus on repairing, reinforcement and exterior in harmony with environment for structure maintenance and performance improvement. The research is about eco friendly durable painting applicable to concrete structure using civil and architecture. it purpose to improve external beauties and durable problems due to flexibility by variation of temperature, adhesion of exterior wall, crack and delamination in existing organic and mineral painting. For those problems, we made a eco friendly pre-paint that is made with preliminary treatment mixture as a highly enriched waterproof agent and adhesive increasing agent in preprocessing mixture. Then we performed an experiment on durability of prevention neutralization of concrete, durability abrasion, hiding power, adhesion, temperature resistance and resistance to chemical attack. The result of an experiment shows that hiding power is over 0.96 in standard test, durability abrasion test got higher value 1mg than water paint 75mg and tensile strength is 6 times higher than standard waterproof specification.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.55-63
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• 2020

This study investigates the mechanical properties and reaction products of activated slag pastes depending on gypsum presence and calcium carbonate addition in terms of compressive strength tests and synchrotron X-ray diffraction. The chemicals of CaO and NaOH are used as activators with different two dosages. The reaction of CaO-activated slag without gypsum just accelerated by addition of calcium carbonate at early ages, but no improvement was observed at later ages. On the other hand, the mechanical properties of CaO-activated slag pastes with gypsum were improved with calcium carbonate, enhancing the stability of ettringite. The variation of mechanical properties of NaOH-activated slag pastes was negligible depending on calcium carbonate addition in case of no gypsum. The addition of calcium carbonate into NaOH-activated slag pastes with gypsum deteriorated its mechanical properties due to the ion competition between CO₃^2- ions and SO₃^2- ions, decreasing crystallinity of reaction products.

• Journal of the Korean Geotechnical Society
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• v.20 no.9
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• pp.77-89
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• 2004

While limit states design (LSD) is currently the standard structural design practice, it is relatively new in the geotechnical design. Adoption of LSD far geotechnical design is an international trend. In the present study, various LSD codes from the United States, Canada, and Europe were reviewed. A simple first-order-second-moment (FOSM) reliability analysis was performed to determine theoretically the ranges of load and resistance factor values for representative loads and foundation bearing capacity, respectively. In order for foundation design to be consistent with current structural design practice, it would be desirable to use the same loads, load factors and load combinations. The values of load factor, obtained from the FOSM analysis, were found to be generally consistent with those given in the codes, whereas the values of resistance factor indicated overall lower ranges due to high values of coefficient of variation used in the analysis. Since the degree of uncertainties included in bearing capacity of foundations varies with the methods used to estimate the bearing capacity, different values of resistance factor should be used fur different methods. For the purpose, continuous efforts are needed to be made first to accurately identify and quantify the uncertainties in the methods.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.343-348
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• 2009

In this study, an efficient sequential bridging method to characterize both the particle size effect and concentration effect on the mechanical properties of nanocomposites at high volume fraction is suggested through a molecular dynamics(MD) simulations and micromechanics of composites materials. The Young's modulus and the shear modulus of the nanocomposites at various particle radius and at 12% volume fraction were obtained from MD simulations and multi-inclusion model was adopted to describe both modulus in continuum model. In order to describe the particle size effect, an additional phase, effective interface, was adopted as characteristic phase and the non-dilute concentration effect which appears at 12% volume fraction was describe via the variation of the elastic modulus of the infinite medium. Both the elastic modulus of the interface and infinite medium were fitted into functions of particle radius for the applicability of the present bridging method at various particle radii. Using the present bridging method the elastic modulus of the nanocomposites was efficiently obtained with accuracy. In addition, the effect of the interface thickness and modulus on the elastic modulus of the nanocomposite was investigated.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.2
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• pp.121-128
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• 2020

The purpose of this study is to investigate the distribution patterns of displacement and acceleration fields in a nonlinear soil ground based on the interaction of high-speed train, wheel, rail, and ground. For this purpose, a high-speed train in motion was modeled as the actual wheel, and the vertical contact of wheel and rail and the lateral contact, caused by meandering motion, were simulated; this simulation was based on the moving mass analysis. The soil ground part was given the nonlinear behavior of the upper ground part by using the modified the Drucker-Prager model, and the changes in displacement and acceleration were compared with the behavior of the elastic and inelastic grounds. Using this analysis, the displacement and acceleration ranges close to the actual ground behavior were addressed. Additionally, the von-Mises stress and equivalent plastic strain at the ground were examined. Further, the equivalent plastic and total volumetric strains at each failure surface were examined. The variation in stresses, such as vertical stress, transverse pressure, and longitudinal restraint pressure of wheel-rail contact, with the time history was investigated using moving mass. In the case of nonlinear ground model, the displacement difference obtained based on the train travel is not large when compared to that of the elastic ground model, while the acceleration is caused to generate a large decrease.

• Korean Journal of Materials Research
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• v.19 no.4
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• pp.198-202
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• 2009

For use in ultrasonic actuators, we investigated the structural and piezoelectric properties of $(1\;-\;x)Pb(Zr_{0.515}Ti_{0.485})O_3$ - $xPb(Sb_{1/2}Nb_{1/2})O_3$ + 0.5 wt% $MnO_2$ [(1 - x)PZT - xPSN + $MnO_2$] ceramics with a variation of x (x = 0.02, 0.04, 0.06, 0.08). All the ceramics, which were sintered at $1250^{\circ}C$ for 2 h, showed a typical perovskite structure, implying that they were well synthesized. A homogeneous micro structure was also developed for the specimens, and their average grain size was slightly decreased to $1.3{\mu}m$ by increasing x to 0.8. Moreover, a second phase with a pyrochlore structure appeared when x was above 0.06, which resulted in the deterioration of their piezoelectric properties. However, the 0.96PZT-0.04PSN+$MnO_2$ ceramics, which corresponds with a morphotropic phase boundary (MPB) composition in the (1 - x)PZT - xPSN + $MnO_2$ system, exhibited good piezoelectric properties: a piezoelectric constant ($d_{33}$) of 325 pC/N, an electromechanical coupling factor ($k_p$) of 70.8%, and a mechanical quality factor ($Q_m$) of 1779. The specimens with a relatively high curie temperature ($T_c$) of $305^{\circ}C$ also showed a significantly high dielectric constant (${\varepsilon}_r$) value of 1109. Therefore, the 0.96PZT - 0.04PSN + $MnO_2$ ceramics are suitable for use in ultrasonic vibrators.

• Korean Journal of Materials Research
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• v.5 no.6
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• pp.748-753
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• 1995

Solid solution of NaNb $O_3$70 mol% and SrTi $O_3$30 mol% was single phase. A broad dielectric peak was found at about l00K. Crystal structure was analysed at room temperature and 12K using Rietveld analysis. The unit cell was assigned to have a a doubled lattice parameter of simple perovskite sturcture at room temperatue, the structure was orthorombic with space group Pmmn. At 12K, the structure was also orthorombic with space group Pnma. This structure change with temperature was due to the distortion of oxygen octahedron. This distortion of oxygen octahedron was made by the decrease of (Ti, Nb)-O bounds length with no variation of (Ti, Nb)-O-(Ti, Nb) bound angle. Therefore the broad dielectirc peak about l00K was attributed to the structural change casued by oxygen octahedron distortion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.1
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• pp.67-76
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• 2011

The use of glass-fiber-reinforced polymer (GFRP) bars in reinforced concrete (RC) structures has emerged as an alternative to traditional RC due to the corrosion of steel in aggressive environments. Although the number of analytical and experimental studies on RC beams with GFRP reinforcement has increased in recent decades, it is still lower than the number of such studies related to steel RC structures. This paper presents the experimental moment deflection relations of GFRP reinforced beam which are spliced. Test variables were different reinforcement ratio and cover thickness of GFRP rebars. Seven concrete beams reinforced with steel GFRP re-Bars were tested. All the specimens had a span of 4000mm, provided with 12.7mm nominal diameter steel and GFRP rebars. All test specimens were tested under 2-point loads so that the spliced region be subject to constant moment. The experimental results show that the ultimate moment capacity of beam increasing of the reinforcement ratio. Failure mode of these specimens was sensitively vary according to the reinforcement ratio. The change of beam effective depth, which was caused by cover thickness variation, controlled the maximum strength and deflection because of cover spalling in tension face.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.2
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• pp.110-121
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• 2016

In the decision-making, such as selection of structure, construction method, or time and scheme of maintenance, the evaluation of life-cycle cost(LCC) is of great importance. The maintenance cost occupy a large portion of the LCC of the railway track as well as the initial construction cost. Futhermore, the proportion of the maintenance cost is much higher in the ballasted track. Thus, the importance of the LCC evaluation is higher than in any other engineering structures. In this study, a LCC model that can consider various design parameters such as the type of track structure, annual traffic volume, axle load, train speed, and proportion of curve sections and engineering structures has been developed. Fundamental data for calculating costs also have been presented. Based on the model and data proposed, the trends in the variation of LCC according to the design parameters were examined and the most important design parameters in the LCC analysis of railway track were investigated. The results show that the proportion of renewal and operational costs is much higher in the ballasted track than in the concrete track, and the annual traffic volume and ballast taming period are most significant factors on the LCC of the ballasted track. On the contrary, it is revealed that the proportion of the initial construction costs in the concrete track is much higher, and the LCC of the concrete track is less sensitive to the traffic volume, train speed, and axle load.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.92-103
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• 2015

Box-Wilson experimental design method, known as central composite design, is the design of any information-gathering exercises where variation is present. This method was devised to gather as much data as possible in spite of the low design cost. This method was employed to model the effect of mixing factors on several performances of 60 MPa high strength self compacting concrete and to numerically calculate the optimal mix proportion. The nonlinear relations between factors and responses of HSSCC were approximated in the form of second order polynomial equation. In order to characterize five performances like compressive strength, passing ability, segregation resistance, manufacturing cost and density depending on five factors like water-binder ratio, cement content, fine aggregate percentage, fly ash content and superplasticizer content, the experiments were made at the total 52 experimental points composed of 32 factorial points, 10 axial points and 10 center points. The study results showed that Box-Wilson experimental design was really effective in designing the experiments and analyzing the relation between factor and response.