• Journal of the Korea Institute of Building Construction
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• v.15 no.2
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• pp.185-192
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• 2015

Expansion joint is the essential element of the bridge in many cases. When the bridge faces chloride of preventing freezing on the surface of the bridge, the expansion joints is damaged significantly, thus this reduces service life and increases maintenance cost of the bridge. As a solution of this problem, new technology using high ductile materials for the joint without expansion joint was developed and in this research, crack control performance, preventing leaking after the cracking, and chloride resistance were experimentally evaluated. As a result of the experiment, with PCM and FRC materials, the connecting joint suffered poor crack dispersion and severe damage by the chloride penetration while with high-ductile material, the connecting joint dispersed the tensile deformation to microcracks stably up to 7.5mm. Furthermore, under the sever conditions, the leaking was prevented and penetration of chloride ions was prevented after the crack occurred.

• Journal of Periodontal and Implant Science
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• v.36 no.2
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• pp.473-488
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• 2006

Adequate bone quality and stress distribution to the bone are of decisive importance for implant success. Even though the success rates of dental implants have been high, implant failures do occur. Overloading has been identified as a primary factor behind dental implant failure. The purpose of this study was to theoretically investigate the effect of two types of implants on the stress distribution in poor bone quality. Employing the finite element method, the study modeled a 4.1 mm diameter, 12.0 mm length implant placed in cortical or spongeous bone. A static loading of lOON was applied at the occlusal surface at 0, 30 degrees angle to the vertical axis of the implant. von Mises stresses concentrations in the supporting bone were analyzed with finite element analysis program. The results were as follows; 1. The stresses at the marginal bone were higher under buccal oblique load(30 degrees off of the long axis) than under vertical load. 2. Under buccal oblique load, the stresses were higher at the lingual marginal bone than at the buccal marginal bone, and the differences were almost the same. 3, Under vertical and oblique load, the stress was the highest at the marginal bone and lowest at the bone around apical portions of implant in cortical bone. 4, Under vertical load, Model 1 showed more effective stress distribution than Model 2 irrespective of bone types. On the other hand, Model 2 showed lower stress concentration than Model 1 under buccal oblique load.

• The Korean Journal of Quaternary Research
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• v.14 no.1
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• pp.65-71
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• 2000

The growth of Daphniphyllum macropodum at Mt. Naejang National Park(Naejang temple area) was investigated in connection with the climatic factors by the use of tree-ring analysis. A pair of cores was extracted from each of 18 trees in the D. macropodum community area near Younjabong for the analysis. The period of mater chronology based upon D. macropodum covers from 1915 to 1998. The growth rates of D. macropodum were very poor in the years 1920, 1932, 1934, 1937, 1942, 1946, 1964, 1969 and 1985, respectively. Response function was employed to understand the relationship between the growth of D. macropodum and climatic factors. The response function of the growth rates of D. macropodum indicated significant negative correlation with the precipitation of August and September. Poor growth of D. macropodum during the August and September nay be due to the frequent rain periods during the summer The heavy rain during the summer seems to decrease the solar radiation, which eventually caused the decrease of photosynthesis capacity. In conclusion, we hypothesize that the decrease of the photosynthesis rates during the rainy summer seasons may cause the slower growth of D. macropodum.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.55 no.3
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• pp.146-152
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• 2006

In order to analyze the characteristics of series arcs that could happen in poor connections of electrical facilities, we made an apparatus which is similar to actual situation. series arcs are generated between copper and copper, copper and bronze, copper and brass, bronze and bronze, and then oxidation growth and voltage waveform were measured. A very small vibration with constant movement is needed to grow oxidation initially, whereas oxidation growth proceeded without a vibration after a certain amount of time. At first, blue white flame was generated initially between copper and copper, and then yellow flame was generated. In case of contact between copper and copper, the length of oxidation growth was about 7.1[mm] in 90[min]. In case of contact between copper and brass, the length of oxidation growth was about 4.3[mm] in 90[min], When bronze is contacted with copper, the lengths of oxidation growth were about 1.4[mm] in 20[min] and 2.7[mm] in 40[min] respectively, and no more oxidation growth was shown after that. In case of contact between brass and brass, the length of oxidation growth was about 1.2[mm] in 90[min], so it was the smallest compared to other cases. When copper is contacted with copper, the current through the load was about 1.6[A] and the power dissipation increased from 19[W] to 31[W]. In case of oxidation growth between copper and brass, the voltage changed from 8.4[V] to 11[V]. However, the voltage drop and the power dissipation between copper and brass were small compared to oxidation growth between copper and copper. When series arcs were generated between bronze and copper, a peak was shown at the beginning of voltage increase, and 40[min] later, oxidation material was not grown any longer. When oxidation growth occurred, voltage waveform showed irregular waveforms with tiny ripples.

• International Journal of Highway Engineering
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• v.8 no.4 s.30
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• pp.25-36
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• 2006

Through field surveys and evaluation on several widened concrete pavements, issues on construction and design related problems are broken down into three categories to be discussed; poor smoothness, influence of traffic vibration on concrete curing, and poor connection to the existing pavement. There are many places where about 100mm only of the marginal strip is removed and where defects such as widening and faulting are observed. Also cracks arise again from the patched areas due to stress concentration near the joint. Roughness on the widened concrete pavement was evaluated and there are some stations where the smoothness limit is over passed. For design consideration, shortage of the required force in the tie-bar is expected in case of road widening specially from 3 lanes to 4 lanes. Finally the average pull-out force of specimens made from the current practice was about 57% of the required force. New connecting methods were suggested in this study.

• Journal of Soil and Groundwater Environment
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• v.8 no.2
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• pp.1-8
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• 2003

Two types of ground-water sampling techniques for CFCs (chlorofluorocarbons) analysis, the cold-welded copper tube method and flame-sealed borosilicate glass ampule method, were compared and evaluated. CFCs concentrations by the copper tube method showed a poor reproducibility among triplicates whereas those by the glass ampule method showed a good agreement and relative standard deviations of triplicates were less than 5%. The poor reproducibility of the copper tube method appears to be attributed to the incomplete sealing in connection between faucets of wellhead and the sampling apparatus. The copper tube method also showed higher CFCs concentrations than the glass ampule method, which is more pronounced for CFC-11 than for CFC-12. The plastic tubings and rubber gasket of faucets in case of the copper tube method possibly contaminated the samples with CFC-11 and CFC-12. The potential of CFCs contamination for the glass ampule method was eliminated by using stainless steel and Nylon only and by connecting the sampling equipment directly to the main discharge pipe of wellhead. The validity of the glass ampule method were also verified by detecting very low level of CFCs for the ground-water sample which is old enough to have negligible CFCs.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.385-396
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• 2014

Traditionally, domestic steel design and construction practice has provided extra shear studs to moment frame beams even when they are designed as non-composite beams. In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange side was prevalent. The upward moving of the neutral axis due to the composite action between steel beam and floor deck was speculated to be one of the critical causes. In this study, full-scale seismic testing was conducted to investigate the side effects of the composite action in steel seismic moment frames. The specimen PN700-C, designed following the domestic connection and floor deck details, exhibited significant upward shift of the neutral axis under sagging (or positive) moment, thus producing high strain demand on the bottom flange, and showed a poor seismic performance because of brittle fracture of the beam bottom flange at 3% story drift. The specimen DB700-C, designed by using RBS connection and with the details of minimized floor composite action, exhibited superior seismic performance, without experiencing any fracture or concrete crushing, almost identical to the bare steel counterpart (specimen DB700-NC). The results of this study clearly indicate that the beams and connections in seismic steel moment frames should be constructed to minimize the composite action of a floor deck if possible.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.5
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• pp.1-12
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• 2019

The purpose of this study is to enhance the seismic performance of exposed column-base plate weak-axis connections for small-sized steel buildings. According to the site inspection for the small-sized building construction, the arbitrary connection details in steel buildings have been applied at the job site, which is considered to be insufficient to guarantee structural safety and stability considering the increased seismic risk in Korea. Therefore, a series of test programs had been done to develop enhanced connection details in order to ensue the adequate seismic stability and safety of small-sized steel buildings. From the test results, It was found that the exposed column-base plate weak-axis connections commonly used in Korea shows very poor seismic behavior due to the "Rocking" phenomena caused by the residual plastic deformation of anchor bolts between anchor plate and concrete. A series of hysteretic tests for finding that solution were conducted to reduce the "Rocking" phenomena of the column-base plate connections, and local buckling of webs in H-column. Finally the enhanced stable seismic behavior was obtained by reinforcing at least 8 anchor bolts with good bonding strength and stiffeners to the webs in H-column.

• Journal of Electrical Engineering and Technology
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• v.1 no.3
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• pp.351-358
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• 2006

In this paper, the electrical characteristics of the contactless transformer is presented using the conventional coupled inductor theory. Compared with the conventional transformer, the contactless transformer has a large airgap, long primary wire and multi-secondary wire. As such, the contactless transformer has a large leakage inductance, small magnetizing inductance and poor coupling coefficient. Therefore, large magnetizing currents flow through the entire primary system due to small magnetizing inductance, resulting in low overall system efficiency. In high power applications, the contactless transformer is so bulky and heavy that it needs to be split by some light and small transformers. So, the contactless transformer needs several small transformer modules that are connected in series or parallel to transfer the primary power to the secondary one. This paper shows the analysis and measurement results of each contactless transformer module and comparison results between the series- and parallel-connection of the contactless transformer. The results are verified on the simulation based on the theoretical analysis and the 30kW experimental prototype.

• Proceedings of the KIEE Conference
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• 2009.07a
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• pp.2158_2159
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• 2009

본 논문에서는 DC전원설비 접속부에서의 접촉불량에 의한 발열 특성에 대하여 실험, 분석하였으며 사용된 DC 전원설비는 상용 교류전원을 직류전원으로 변환하는 AC/DC 컨버터의 출력전원을 이용하는 LED 가로등 조명설비의 전원 접속부을 대상으로 하였다. 외부의 기계적 진동에 의해 동전선 접속부에 아크와 열이 발생하며 이때 발생한 발열 온도와 열 분포를 측정하였으며 적열부가 형성된 후 25분이 경과하였을 때 최고 $842.68^{\circ}C$까지 온도가 상승하였으며 접속부의 접촉전압은 1.5~1.6V, 통전전류는 6.6~6.9A로 약간의 변화만 나타남을 볼 수 있었다. 또한 DC전원에서 동전선 접속부에서의 산화물 생성과 증식 거동에 대하여 분석하였으며 AC전원에서와 유사하게 산화물이 형성되어 성장함을 볼 수 있었다. 이러한 실험과 분석 결과는 향후, DC 전원설비에서의 전기화재 예방을 위한 자료로 활용 가능할 것으로 기대된다.