• Journal of Korean Tunnelling and Underground Space Association
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• v.7 no.2
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• pp.143-152
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• 2005

Shotcrete for support of tunnel structures may contact with groundwater. The hazardous components in groundwater may cause corrosion of shotcrete. Also, the hazardous components may deteriorate the engineering properties of shotcrete, such as compressive strength, bond strength, flexural strength and so forth. The more the effect of the hazardous components on the shotcrete may increase, the more the stability of tunnel structure may decrease. The specimens were artificially immersed in various chemical solutions including hazardous components after the specimens were made at the tunnel construction site. It was performed to analyze the effect of the hazardous components in ground water on the engineering properties of shotcrete. The uniaxial compressive strength test, XRD, SEM were conducted to evaluate the durability and corrosion of shotcrete.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.4
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• pp.395-402
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• 2017

Recently, many researches on crack healing and repairing technique using bacteria which can produce vital-reacted calcite have been proposed. This study is for a basic research on repair material with slime formation through bacteria and deals with durability evaluation for coating materials containing bacteria-forming slime. For the work, 4 types of bacteria (Rhodobacter capsulatus, Rhodopseudomonas palustris, Bacillus thuringiensis, and Bacillus subtilis) and 2 types of nutrient conditions are considered, and several tests covering strength evaluation under sulfate condition, accelerated chloride diffusion, and UV (Ultrasonic Velocity) measurement are performed. Strength improvement in coating materials containing bacteria is evaluated in spite of even exposure to sulfate attack to 7 days. Chloride diffusion coefficient and UV properties are also improved except for the case of Rhodopseudomonas palustris. With resistance of slime to long term exposure and aerobic conditions for bacteria longevity, the proposed bacteria shows an engineering feasibility for repair material of RC structure exposed harsh environment.

• Journal of the Korean Society of Propulsion Engineers
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• v.15 no.4
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• pp.18-25
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• 2011

Solid propulsion systems have simple structures compared to other propulsion systems and are suitable for long-term storage. However the systems generally have limits on control of thrust levels. In this paper we suggest control algorithms for combustion chamber pressure of variable thrust solid propulsion systems using special nozzles such as pintle valve. For the pressure control within the chamber, we use a simple pressure change model by considering only mass conservation within the combustion chamber, design a classical algorithm and also a nonlinear controller using the feedback linearization technique. Also we derive the equation of the thrust for an under-expanded one-dimensional nozzle and then design a proportional-intergral controller after linearizing the thrust model for an operating point. Finally, we demonstrate the performance of the controller through a numerical simulation.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.773-776
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• 2008

Restraining cracks on concrete structures can be the basic condition to improve the durability, so in this research, the resistibility on the drying shrinkage of concrete structures in the long period was being confirmed and as the reason of this shrinkage, the density of minute textures was being analyzed using a wooden prototype of a full scale produced with ready-mixed concrete and agents of glycol which can be used as a surfactant. As result of those tests, PFB technology can reduce the drying shrinkage by approximately $-100{\sim}200{\times}10^{-6}$ on a wooden prototype of a full scale and can also reduce the pore volume as the obstruction to the movement of gas or liquid by approximately $2.4{\sim}3.5$% so that PFB technology can be used to assure the resistibility on the drying shrinkage.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.8 no.2
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• pp.135-142
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• 2010

To obtain the input data for the design and long-term performance assessment of a high-level waste repository, the thermal conductivities of several granite rocks which were taken from the rock cores from the declined borehole were measured. The thermal conductivities of granite were measured under the different conditions of water content to investigate the effects of the water content on the thermal conductivity. A simple empirical correlation was proposed to predict the thermal conductivity of granite as a function of effective porosity and water content which can be measured with relative ease while neglecting the possible effects of mineralogy, structure and anisotropy. The correlation could predict the thermal conductivity of granite with the effective porosity below 2.7% from the KURT site with an estimated error below 10%.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.1-7
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• 1994

As a subsequent work presented in Ref.[1] which deals with the global dynamic wave loads in the classification rules, further studies on such as the dynamic pressures above load waterline, motions and accelerations and other local design loads were carried out. Frequency domain 2D linear strip theory is employed and statistical analyses for the concerned ship responses were carried out for the 17 existing ships to derive simple and descriptive formula which can be used as a guidelines at preliminary design stage as well as a part of classification rules. The calculated results and thereby proposed formula are compared with those of other available data, and will be incorporated in the rules for steel ships of Korean Register of Shipping.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.3
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• pp.297-308
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• 2023

Displacement of structures is the most important parameter for safety and performance assessment and is measured to use for diagnosis and maintenance of bridges. Usually LVDT, Laser and GNSS are used for displacement measurement but these measurement instruments have problems in terms of field condition and cost. Therefore, in this study, displacements were evaluated using rotational angle measured by inclinometers and the proposed algorithm was experimentally verified. As the result, vertical displacements of cable supported bridges with traffic and temperature load were properly evaluated through the proposed algorithm. Therefore it is considered that the proposed algorithm can be used for displacement measurement by vehicle load test and long term displacement monitoring.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.147-152
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• 2009

The compressive strength test, bulk density and mortar absorption ratio were carried out to utilize the data as the basic sources for the lightweight mortar and the lightweight concrete, through the study on the physical characteristics of the artificial lightweight aggregate (ALA) made of waste glasses, which was developed for the first time in the country. On the basis of these experiments, the density and the unit volume weight of the ALA showed the value less than 50% of the common aggregate due to the independent pore structure, and the mortar that contains ALA had no big difference from the Control mortar in the test of the absorption ratio. It is judged that this happens based on the internal independent pore structure of the ALA. In case of the mortar containing ALA, there was a tendency of declination in the compressive strength and the bending strength as the mixing rate is increasing, but all mortar showed more than 70% of the Control mortar compressive strength except for the La50 mortar. Hereafter, it is judged that according to the control of the mixing ratio of mineral admixing agent, water and cement, it will realize the equal strength to the control mortar, and the long term edurance is needed to be considered together.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.4
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• pp.355-362
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• 2012

Remaining useful life(RUL) prediction of a system is important in the prognostics field since it is directly linked with safety and maintenance scheduling. In the physics-based prognostics, accurately estimated model parameters can predict the remaining useful life exactly. It, however, is not a simple task to estimate the model parameters because most real system have multivariate model parameters, also they are correlated each other. This paper presents representative methods to estimate model parameters in the physics-based prognostics and discusses the difference between three methods; the particle filter method(PF), the overall Bayesian method(OBM), and the sequential Bayesian method(SBM). The three methods are based on the same theoretical background, the Bayesian estimation technique, but the methods are distinguished from each other in the sampling methods or uncertainty analysis process. Therefore, a simple physical model as an easy task and the Paris model for crack growth problem are used to discuss the difference between the three methods, and the performance of each method evaluated by using established prognostics metrics is compared.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.3
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• pp.47-56
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• 2020

In this study, three levels of W/B(Water to Binder) ratio (0.37, 0.42, 0.47) and substitution ratio of GGBFS (Ground Granulated Blast Furnace Slag) rate (0 %, 30 %, 50 %) were considered to perform RCPT (Rapid Chloride Diffusion Test) at the 1,095 aged day. Accelerated chloride diffusion coefficient and passed charge of each concrete mixture were assessed according to Tang's method and ASTM C 1202, and improving behaviors of durability performance with increasing aged days are analyzed based on the test results of previous aged days from the preceding study. As the age of concrete increases, the passed charge and diffusion coefficient have been significantly reduced, and especially the concrete specimens containing GGBFS showed a significantly more reduction than OPC(Ordinary Portland Cement) concrete specimen by latent hydraulic activity. In the case of OPC concrete's results of passed charge, at the 1,095 days, two of them were still in the "Moderate" class. So, if only OPC is used as the binder of concrete, the resistance performance for chloride attack is weak. In this study, the time-parameters (m) were derived based on the results of the accelerated chloride diffusion coefficient, and the deterministic and probabilistic analysis for service life were performed by assuming the design variable as a probability function. For probabilistic service life analysis, durability failure probabilities were calculated using Monte Carlo Simulation (MCS) to evaluate service life. The service life of probabilistic method were lower than that of deterministic method, since the target value of PDF (Probability of Durability Failure) was set very low at 10 %. If the target value of PDF suitable for the purpose of using structure can be set and proper variability can be considered for each design variable, it is believed that more economical durability design can be made.