• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.173-181
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• 2021

Reinforced concrete structures are exposed to various environments, resulting in reinforcement corrosion due to moisture and ions penetration. Reinforced concrete corrosion causes a decrease in the durability performance of reinforced concrete structures. One solution to mitigate such issues is using FRP rebars, which offer several advantages such as high tensile strength, corrosion resistance, and light-weight than conventional rebars, in reinforced concrete instead of conventional steel rebars. The FRP rebar used should be examined at the limit state because FRP reinforced concrete has linear behavior until its fracture and can generate excessive deflection due to the low elastic modulus. It should be considered while designing FRP reinforced concrete for flexure. In the ultimate limit state, the flexural strength of FRP reinforced concrete as per ACI 440.1R is significantly lower than the flexural strength by applying both the environmental reduction and strength reduction factors accounting for the material uncertainty of FRP rebar. Therefore, in this study, the experimental results were compared with the deflection of the proposed effective moment of inertia referring to the local and international standards. The experimental results of GFRP and BFRP reinforced concrete were compared with the flexural strength as determined by ACI 440.1R and Fib bulletin 40. The flexural strength obtained by the experimental results was more similar to that obtained by Fib bulletin 40 than ACI 440.1R. The flexural strength of ACI 440.1R was conservatively evaluated in the tension-controlled section.

• Journal of the Korean Institute of Gas
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• v.26 no.6
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• pp.16-23
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• 2022

In this study, characteristics of effect on hydrogen gas was investigated to hydrogen embrittlement by disk and tensile tests. The developed and commercial alloy was fabricated to a plate material made from an alloy ingot. The prepared materials were processed in the form of a disk to measure rupture pressure by hydrogen and helium gas at a rate of 0.1 to 1,000 bar/min. In the hydrogen pre-charged tensile test, a specimen was hydrogenated using an anode charging method, and the yield strength, ultimate tensile strength, elongation, and reduction in area rate were carried by a strain rate test. Also, the microstructure was observed to the fracture surface of the tensile test specimen. As a result, the developed materials satisfied endurable hydrogen embrittlement, and the fractured surface showed a brittleness fracture surface with a depth of several ㎛, but dimple due to ductile fracture could be observed.

• Journal of the Korean Geotechnical Society
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• v.22 no.10
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• pp.77-91
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• 2006

Domestic practices in shotcrete use have developed in many respects even now, but it still has issues about material, construction, quality standard and so on. In overseas, the construction using high strength shotcrete with $39.2{\sim}58.8 MPa$ of compressive strength is becoming common based on the shotcrete technology of high strength and durability. However, domestic shotcrete design strength is low at around 20.6 MPa of compressive strength and a long term durability is also insufficient. In this paper, field tests using high-quality additives and accelerators were performed to obtain the improvement of shotcrete strength and EFNARC standard was used to evaluate the field test results. In addition, deterioration test combined with the freezing-thawing and carbonation was also performed in order to investigate a long-term durability of high-strength shotcrete. As a result of the field test, the promotion ratio of early strength was $90{\sim}97%$ in case of using alkali-free accelerators. And the compressive strength of the shotcrete using Micro-silica fume was $45.2{\sim}55.8MPa$ and flexible strength was $5.01{\sim}6.66MPa$, so the promotion ratio of strength was $37{\sim}79%$ and $17{\sim}61%$ respectively. The promotion effect of strength by silica fine additives ratio of $7.5{\sim}10%$ for cement mass was much superior to the other cases. It was especially examined that using Micro-silica fume reduced deterioration due to mixed steel fiber and improved a long-term durability of shotcrete.

• Nuclear Engineering and Technology
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• v.18 no.1
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• pp.1-8
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• 1986

A magnetic quadrupole doublet was fabricated for use at the pre-target position of SNU 1.5MV Van de Graaff accelerator and then its optical characteristics were measured and analysed. The physical dimensions are: pole length 180mm, aperture radius 25mm, pole tip radius 28.75mm. Material for poles and return yokes is carbon steel KS-SM40C. Coils have 480 turns per one pole and air-cooling is adopted. Applying the d.c. current 2.99$\pm$0.03A to the lens, and using the Hall probe, magnetic field elements $B_{\theta}$ , $B_{\gamma}$, were measured at the selected Points along each coordinate direction r,$\theta$, z. From the area integration and orthogonal polynomial fitting for the measured data, the magnetic Field gradient G=566.3$\pm$2.1 gauss/cm at lens center, the effective length L=208.3$\pm$1.44mm along the lens axis have been obtained. The harmonic contents were determined up to 20-pole from the generalized least squares fitting. The results indicate that sextupole/quadrupole is below 1.4$\pm$0.9% and all the other multipoles are below 0.5% in the region within 18mm radius at the center of lens.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.565-571
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• 2008

Recently, the evaluation technique using NDT (Nondestructive Technique : NDT) is widely utilized because it makes little damage on RC (Reinforced Concrete : RC) structures. The techniques using electromagnetic properties (EM properties) are also attempted for the evaluation of the performance of concrete which is nonmetallic. For the economic manufacturing of concrete material, sea-sand is often used as aggregate, however, chloride ion in concrete has direct effects on steel corrosion and EM properties. In this study, OPC mortar specimens with 5 different chloride amount (0.0, 0.6, 1.2, 2.4, and $3.6kg/m^3$) and 3 different water-cement ratios (45%, 55%, and 65%) are prepared in order to investigate the EM properties corresponding to concrete properties. The EM properties of conductivity and dielectric constant are measured in the frequency range over 0.2~20 GHz. To facilitate the comparison of EM properties with chloride content, average values are taken respectively for the conductivity and dielectric constant measured over the 5~20 GHz frequency range. According to the results of this experiment, dielectric constant and conductivity are increased with lower W/C ratio and larger amount of chloride content.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.259-267
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• 2008

The ultimate strengths of reinforced concrete deep beams are governed by the capacity of the shear resistance mechanism composed of concrete and shear reinforcing bars, and the structural behaviors of the beams are mainly controlled by the mechanical relationships according to the shear span-to-effective depth ratio, flexural reinforcement ratio, load and support conditions, and material properties. In this study, a simple indeterminate strut-tie model reflecting all characteristics of the ultimate strengths and complicated structural behaviors is presented for the design of simply supported reinforced concrete deep beams. In addition, a load distribution ratio, defined as a magnitude of load transferred by a vertical truss mechanism, is proposed to help structural designers perform the design of simply supported reinforced concrete deep beams by using the strut-tie model approaches of current design codes. In the determination of a load distribution ratio, a concept of balanced shear reinforcement ratio requiring a simultaneous failure of inclined concrete strut and vertical steel tie is introduced to ensure the ductile shear failure of reinforced concrete deep beams, and the prime design variables including the shear span-to-effective depth ratio, flexural reinforcement ratio, and compressive strength of concrete influencing the ultimate strength and behavior are reflected upon based on various and numerous numerical analysis results. In the companion paper, the validity of presented model and load distribution ratio was examined by employing them to the evaluation of the ultimate strengths of various simply supported reinforced concrete deep beams tested to failure.

• Resources Recycling
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• v.32 no.6
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• pp.67-78
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• 2023

The rare metals used as raw materials in high-tech industries undergo changes in demand structures and supply chains following domestic industrial structural shifts and technological advancements, exhibiting high price volatility. Therefore, it is necessary to periodically analyze changes in the demand structures of rare metals. Since domestic demand for most rare metals relies on imports in Korea, the changes in domestic demand for rare metals can be identified by analyzing changes in their trade structure. In the present study, we analyze the changes in trade volume, trade growth rate, trade rankings, and trading countries from 2000 to 2022 for 35 rare metals, categorized into five types-ores, metals, alloys, compounds, and scrap. The trade of the raw materials of rare metals in Korea has generally increased since the 2000s, except for a significant decline in 2009 and 2016. The total trade volume, encompassing both exports and imports, has increased by approximately tenfold in 2022 compared to 2001. Until the mid-2010s, the trade of the raw materials of rare metals was primarily focused on those used in steel-manufacturing such as silicon, nickel, chrome, molybdenum, manganese, and others. However, after that period, there has been an increase in the trade of platinum group metals like palladium, rhodium, platinum, and the raw materials of rare metals for secondary battery-manufacturing such as lithium and cobalt. Particularly in 2022, lithium has become the largest share in trade of the raw materials of rare metals in Korea, due to the price surge and increase in demand.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.6
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• pp.620-627
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• 2023

Ship noise is one of the important factors for the living and health of seafarers, and ef orts to reduce ship noise are actively underway. There are two methods of noise reduction: passive noise Control (PNC) and active noise control (ANC). Unlike cars and airplanes, ANC is not widely used for noise reduction on ships. This study aimed to reduce the noise generated in the engine room by using soundproof panels and high-frequency vibration generators, as well as active noise control (ANC). For this purpose, an experimental model was made using an acrylic box, and the noise reduction effect was measured under four conditions. The experimental results are as follows: First, the soundproof panel had a noise reduction effect in all ranges from 55 dB to 85 dB. In the case of using a high-frequency vibration generator, there was no ef ect in the low noise range such as 55 dB(A), but there was a noise reduction effect in the high noise range such as 70.8 dB(A) and 85 dB(A).Second, when the soundproof panel and the high-frequency vibration generator were used simultaneously, the noise reduction ef ect was up to -2.2 dB(A). The results of this experiment were obtained from an experimental model made of acrylic, and they may be different from actual ships made of steel plate. In future studies, we plan to experiment using iron plate (considering the material, thickness, and structure) used in actual ships. We hope that this study will help to improve the living environment and health of seafarers on ships.

• The Journal of Engineering Geology
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• v.34 no.2
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• pp.163-171
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• 2024

Changes in the soil layer on Dokdo are important both academically and with regard to sustainable conservation and utilization of the islands. Continuous investigation and observation are necessary, as the soil layer is essential to the growth of plants and, therefore, the islands' ecosystem. Such work was carried out for about 8 years using soil erosion measuring bars, which are durable and facilitate simple monitoring of changes in the soil layer. Each bar comprised a rod measuring 30~50 cm long and 1.5 cm in diameter, and the use of stainless steel afforded resistance to corrosion caused by sea breezes. Six measuring bars were installed in the soil layers of each of two islands, Dongdo and Seodo, and measurements were taken one to three times a year from 2014 to 2021. The field measurements indicate that soil was deposited on Dongdo but eroded on Seodo during the observation period. As the measuring bars on Dongdo were located in the central and lower parts of the island, the observed changes in the soil layer resulted mainly from sedimentation of material eroded by weathering or soil runoff from the upper part of the island. In contrast, the measurement locations on Seodo were located in the upper and central parts of the island, where soil erosion and runoff diminished the soil layer at the observation points.

• Journal of Korean Society of Water and Wastewater
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• v.37 no.4
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• pp.215-229
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• 2023

In this study, non-destructive technologies that can be applied to evaluate the integrity of valve materials, safety against internal pressure caused by corrosion, and the blocking function of large-diameter water valves during operation without requiring specimen collection or manpower entering the inside of the valve were tested to assess the reliability of the technologies and their suitability for field application. The results showed that the condition of the graphite structure inside the valve body can be evaluated directly through the optical microscope in the field without specimen collection for large-diameter water butterfly valves, and the depth of corrosion inside the valve body can be determined by array ultrasound and the tensile strength can be measured by instrumented indentation test. The reliability of each of these non-destructive techniques is high, and they can be widely used to evaluate the condition of steel or cast iron pipes that are significantly smaller in thickness than valves. Evaluation of blocking function of the valves with mixed gas showed that it can be detected even when a very low flow rate of mixed gas passes through the disk along with the water flow. Finally, as a result of evaluating the field applicability of non-destructive technologies for three old butterfly valves installed in the US industrial water pipeline, it was found that it is possible to check the material and determine the suitability of large-diameter water valves without taking samples, and to determine the corrosion state and mechanical strength. In addition, it was possible to evaluate safety through the measurement results, and it is judged that the evaluation of the blocking function using mixed gas will help strengthen preventive response in the event of an accident.