• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.4
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• pp.56-68
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• 2019

Safety-conscious design on site is required for site constructions because of the introduction of the design for safety, but it still leaves much to be desired. This study compared the site where the design was applied and the site where it was not applied. The applied case examined the underground wall construction during frame construction, which corresponds to the skeleton of the building construction. The underground wall construction is quite risky due to the exposure to exterior environments and involvement of various stages, such as scaffolding, formwork, reinforcing work, and concrete casting work. Therefore, the risk factors for each stage were identified and a risk assessment was carried out to select an alternative method to reduce the risk. The risk factors of the selected alternative construction method were also identified and a risk assessment was conducted. The risk assessment weight was calculated by comparing the site where the construction method was applied and the site where it was not, explaining the necessity of the design for safety in reducing the risk. In addition, an actual case where an alternative construction method was used was studied to highlight the necessity for a design for safety.

• Journal of the Korean Geosynthetics Society
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• v.17 no.4
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• pp.29-40
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• 2018

Oil sands, which are largely distributed in Canada and Venezuela, are a mixture of crude oil and sandy soils. In order to extract crude oil from oil sands, construction of massive oil sand plants is required. Generally, the typically-used foundation types of the oil sand plant are driven piles and cast-in-place piles. Most of the oil sand plants are located in cold and remote regions. Installation of driven piles in frozen or organic surface soils is difficult due to high resistance and installation equipment accessability, while the cast-in-place pile has concrete curing problem due to cold temperature. Helical pile can be installed quickly and easily using rotation with a little help of vertical load. As the installation of helical pile is available using a small and light-weight installation equipment, accessibility of installation equipment is improved. The helical pile has an advantage of easy removal by rotation in reverse direction compared with that of installation. Furthermore, reuse of removed helical piles is possible when the piles are structurally safe. In this study, the behavior of helical piles varying helix pitch was analyzed based on the numerical analysis results. Numerical model was calibrated based on the results of model helical pile tests in laboratory. The ultimate helical pile loads, the displacement of each helix attached to the shaft of the helical pile, and the load sharing ratio of each helix were analyzed.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.6
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• pp.957-972
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• 2018

Tunnels constructed in cold regions can cause serious defects such as cracks and leaks due to external temperature changes in the portals and vents. In order to prevent the freezing damage of the tunnel, appropriate measures should be applied to the section where the freeze damage is concerned. However, the specific criteria and contents for judging whether or not the anti-freeze measures are applied are not presented. In this study, the laboratory freezing tests on the temperature changes of the concrete specimens under freezing conditions were carried out. And the freeze-thaw repetition cycle (F), which can judge the possibility of freezing damage, were presented based on the heat transfer quantity (W) by experimental results of case studies. Also, we propose a classification of cold regions considering the climatic characteristics of Korea for using it to efficient design and maintenance.

• Journal of the Korea Institute of Building Construction
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• v.18 no.6
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• pp.507-515
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• 2018

The purpose of this research is to develop a slurry-type accelerator that contains various beneficial properties such as reduction of dust generation, lower alkalinity, early age strength development, etc., and uses such slurry type accelerator to produce high performance shotcrete that present excellent resistant against chloride ion penetration. In this work, shotcrete mixtures of 0.44 and 0.338 water-to-binder ratio (w/b) were produced at construction site using slurry-type accelerator. The mechanical properties and chloride ion penetration resistance of such shotcrete (including base concrete) were evaluated. According to the experimental results, the slurry-type accelerator was successfully used to produce both w/b 0.44 and 0.338 shotcretes. The 1 day and 28 day compressive strength of shotcrete were found to be closer to or higher than 10MPa and 40MPa, respectively. The w/b 0.338 shotcrete that used 40% replacement of blast furnace slag showed lower compressive strength than w/b 0.44 shotcrete without any mineral admixture at 1 day. However, the compressive strength with 40% blast furnace slag increased significantly at 28 day. Moreover, there was more than 50% increase in chloride ion penetration resistance with blast furnace slag, showing its strong potential for higher performance shotcrete application.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.17 no.2
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• pp.167-181
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• 2019

Currently, the development of evaluation technology for vibration and shock load characteristics and spent nuclear fuel structural integrity under normal conditions of transport is being conducted in the Republic of Korea. This is the first such research conducted in the Republic of Korea and, thus, previous international studies need to be investigated and will be referred to in the ongoing project. Before 2000, several studies related to measurement of vibration and shock loads on spent nuclear fuel were conducted in the US. US national research institutes conducted uniaxial fuel assembly shaker tests, concrete block tests, and multi-axis fuel assembly tests between 2009 and 2016. In 2017, multi-modal transportation tests including road, sea, and rail transport were also performed by research institutes from the US, Spain and the Republic of Korea. Therefore, test preparation procedures, acceleration and strain measurement results, and finite-element and multi-body dynamics analysis were investigated. Based on the measured strain data, the preliminary conclusion was obtained that the measured strain was too small to cause damage to spent nuclear fuel rods. However, this conclusion is a preliminary conclusion that only reviews part of the results; a detailed review is being conducted in the US. The investigation of international studies on spent nuclear fuel structural integrity tests considering vibration and shock loads under normal conditions of transport in the US will be useful data for the project being conducted in the Republic of Korea.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.130-134
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• 2019

In this paper, a laser-based non-contact load cell is newly developed for measuring forces in prestressed concrete tendons. First, alumina particles have been sprayed onto an empty load cell which has no strain gauges on it, and the layer has been used as a passive stress sensor. Then, the spectral shifts in fluorescence spectroscopy have been measured using a laser-based spectroscopic system under various force levels, and it has been found that the relation of applied force and spectral shift is linear in a lab-scale test. To validate the field applicability of the customized load cell, a full-scale prestressed concrete specimen has been constructed in a yard. During the field test, it was, however, found that the coating surface has irregular stress distribution. Therefore, the location of a probe has to be fixed onto the customized load cell for using the coating layer as a passive stress sensor. So, a prototype customized load cell has been manufactured, which consists of a probe mount on its casing. Then, by performing lab-scale uniaxial compression tests with the prototype load cell, a linear relation between compression stress and spectrum shift at a specific point where laser light had been illuminated has been detected. Thus, it has a high possibility to use the prototype load cell as a force sensor of prestressed concrete tendons.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.372-381
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• 2019

In this study, the National Disaster Management System (NDMS) was analyzed to evaluate the disaster impact assessment standards for steep slopes. Problems in the assessment methods and systems were discovered, which could be reasons for poor reliability. The disaster-risk evaluation index needs improvement to evaluate various types of retaining walls, such as concrete/reinforced soil walls and reinforcing stone masonry. Additionally, using the same score for overturning, bulging, and efflorescence could be reasons for poor reliability, and different weighting factors are needed. Assessment methods are needed to subdivide the social influence evaluation index while considering environmental conditions of steep slopes, such as railroads and reservoirs. For the evaluation of steep slopes, standards for start and end points of steep slopes should be created for effective management, and disaster impact assessment needs to be performed after redevelopment from an advanced index for protection and reinforcement. These problems were derived from a current evaluation system, so a disaster impact assessment is necessary to supplement the results of this study.

• Journal of Korean Society of Forest Science
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• v.108 no.2
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• pp.224-232
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• 2019

The movement of fish to the upper and the lower parts of a mountain stream was investigated based on the installation of specific types of structures within the stream. The results indicated that as the flow rate increases after a rain, the height of the drop in an open-type structure, such as a concrete box, is decreased so that the floating fishes, such as the Chinese minnow fish, move relatively easily from the upper to the lower parts and from the lower to the upper parts of the stream. In contrast, the fishes released from an upper point of a wall-type structure with <1 m, such as rocks drop works and stone masonry for stream-grade stabilization, were trapped in the lower part of the stream and, even after the rainy season, it was difficult for the fish to move from the lower to the upper parts of the stream. In particular, the barrier-type structures ${\geq}3m$ limit the movement of fish, even when there are few drainage holes at the lower end of the dam, and there is no space for the fishes to communicate with each other, even when the flow rate is high; therefore, although the fish are active, they are restricted to move according to the type and characteristics of the structures. When installing structures in a mountain stream, the height of the structure must be low enough to allow the fish to communicate with each other or an open-type structure must be installed. The fish habitat and water conditions within the stream must be considered when designing the type and height of the in-stream structures.

• Journal of the Korean Recycled Construction Resources Institute
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• v.8 no.4
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• pp.520-527
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• 2020

Hwangtoh is the rich resource that accounts for about 15.0% of the domestic soil, and can be used as the admixture of concrete with Pozzolan characteristics if activated by rapidly freezing after burning with high temperature. In this study, the mortar curbs containing active hwangtoh were produced, based on the mixture for the mortar curbs sold on the market. The substitution rate of active hwangtoh were considered 10.0% and 25.0%, and the test items were selected to compressive and flexural strength tests, freezing/thawing resistance tests, accelerated carbonation tests, and accelerated chloride diffusion tests. In the results of the mechanical performance, it was showed that the highest strength was evaluated in OPC mixture, and the increase in strength was small by the increase of age, which was believed to be due to the fact that most of the strength in each mixture was created in three days of steam curing. The results of the freezing/thawing tests for 28 aged days showed the reduction rate of compressive strength was 85.0% or higher for all specimen, meeting the criteria presented. The accelerated carbonation tests were carried out on the specimen at 28 days of age, and the results showed that the mortar with active hwangtoh had lower carbonation resistance performance than mortar with OPC. The passed charge of each mixture was assessed in accordance with ASTM C 1202 on 28 and 91 aged days. The OPC mixture had "Low" rate and the mortar with active hwangtoh had "Moderate" rate. So it was thought that the mortar with active hwangtoh had appropriate resistance performance for chloride attack.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.417-426
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• 2021

Recently, use of the precast concrete (PC) system, which can increase economy by minimizing field work, has rapidly increased. However, the PC system cannot exhibit structural performance under construction, specifically before integration between members. Furthermore, since it is difficult to secure the structural integrity of beam-column joints even after construction, the PC system is vulnerable to progressive collapse. In the PC system, various types of details for PC beam-column joints have been proposed, while the structural/construction details of PC system generally used in Korea differ from those of overseas PC systems. However, studies on the progressive collapse of the domestic PC system are limited. Thus, in this study, we investigated the structural/construction details of PC beam-column joints mainly used in Korea. Based on the investigation, for the prototype PC system with typical joint details, a nonlinear finite element analysis was carried out to evaluate its structural performance under progressive collapse. Further, a parametric study was performed, and the effect of the design parameters was investigated, to recommend a method to improve the progressive collapse resistance of the PC system.