• Korean Journal of Materials Research
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• v.9 no.9
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• pp.919-925
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• 1999

Grain boundary characteristics and corrosion behavior of Alloy 600 material were investigated using the concept of grain boundary control by thermomechanical treatment(TMT). The grain boundary character distribution (GBCD) was analyzed by electron backscattered diffraction pattern. The effects of GBeD variation on intergranular at tack(JGA) and primary water stress corrosion cracking(PWSeC) were also evaluated. Changes in the fraction of coinci dence site lattice(CSL) boundaries in each cycle of TMT process were not distinguishable, but the total eSL boundary frequencies for TMT specimens increased about 10% compared with those of the commercial Alloy 600 material. It was found from IGA tests that the resistance to IGA was improved by TMT process. However, it was found from PWSCC test that repeating of TMT cycles resulted in the gradual decrease of the time to failure and the maximum load due to change in grain boundary characteristics, while the average crack propagation rate of primary crack increased mainly due to suppression of secondary crack propagation. It is considered that these corrosion characteristics in TMT specimens is attributed to 'fine tuning of grain boundary' mechanism.

• Journal of the Korea institute for structural maintenance and inspection
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• v.21 no.1
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• pp.9-14
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• 2017

In the present work, a mechanical performances under cyclic loading in RC (Reinforced Concrete) beams with normal steel and FRPH (Fiber Reinforced Plastic Hybrid) bar are investigated. For the work, RC beam members with $200{\times}200{\times}2175mm$ of geometry and 24 Mpa of design strength are prepared, and 4-point-bending tests are performed for evaluation of cracking, yielding, and ultimate loads. Through static loading test, 48.9kN and 36.0 kN of yielding loads are measured for normal RC and FRPH beam, respectively. They have almost same ultimate load of 50.0 kN. Typical tension hardening behavior is observed in FRPH beam, which is caused by the behavior of FRPH bar with tension hardening. In cyclic loading conditions, FRPH beam has more smaller crack width and scattered crack pattern, and it shows more elastic recovery than normal RC beam. The energy dissipation ratio in FRPH beam is 0.83, which is greater than 0.62 in normal RC beam and it shows more effective resistance to cyclic loadings.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.393-400
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• 2011

The needs for high strength structural materials have recently increased, because construction and cost efficiencies are demanded by the costumers. But, the use of high strength reinforcing bars requires longer development and splice lengths compared to normal strength bars. This restriction may cause reduction in construction efficiency and require more complicated details. The purpose of this paper is to evaluate the bond strength on the rib shape of reinforcing bars to decrease development and splice lengths of high strength reinforcements. Total of 5 simple beam specimens were tested, and the main test variable was a rib shape of reinforcing bars. Test data was analyzed in the viewpoint of bond strength, load-deflection relationship, and crack pattern. Test results indicated that the bond strength of high relative rib area reinforcing bars increased up to 11% compared to normal strength reinforcements. And the improved rib shape reinforcements, which were formed with high and low height rib, increased the bond strength up to 23% even though the relative rib area was same as the high relative rib area reinforcements. Serviceability performances such as deflection number of cracking, and maximum crack width were similar in all specimens, so it is safe to conclude that the improved rib shape reinforcements can be applied to the structural members.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.225-232
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• 2012

This paper presents the test results on the shear performance of large-size reinforced concrete beams using recycled fine aggregate to evaluate its applicability to structural concrete. The performance of these beams is compared to that of similar beams casted with natural coarse and fine aggregates. All of the beam specimens without shear reinforcement had $400mm{\times}600mm$ rectangular cross section and a shear span ratio (a/d) of 5.0. Five concrete mixtures with different replacement levels of recycled fine aggregates (0, 30, 60, 70 and 100%) were used to obtain a nominal concrete compressive strength of 28MPa. The test results of load-deflection curve, shear deformation, diagonal cracking load, crack pattern, ultimate shear strength, and failure mode are examined and compared. In addition, code and empirical equations from KCI, JSCE, CSA, Zsutty, and MCFT were considered to evaluate the applicability of these equations for predicting shear strength of reinforced concrete beam with recycled fine aggregate. The results showed that the overall shear behavior of reinforced concrete beams incorporating less than 60% recycled fine aggregate was comparable with that of conventional concrete beam. The MCFT gave good prediction and other code equations were conservative in predicting the shear strength of the tested beams. The beam specimens with replacement of 70 and 100% of natural fine aggregates by recycled fine aggregates showed different failure mode than other tested beams.

• Journal of Korean Society of Forest Science
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• v.108 no.4
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• pp.540-551
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• 2019

This study was conducted to provide basic data for classifying patterns of land creep in 37 areas in South Korea using geological and soil property analyses. Geological time, as it relates to land creep areas in South Korea, had been most impactful for the Gyeongsang Supergroup and its sedimentary bedrock during the Cretaceous period. In this area, perfect ridge cliffs in land creeping areas included 20 plots (approximately 54.0%), while tension cracking areas with ambiguous ridge cliff characteristics included 17 plots (approximately 46.0%). Hesitant slide slope types included 20 plots (approximately 54.0%) within theslide slope of an incident pattern (slide slope figure) in land creeping areas. Colluvial debris types among land creep patterns were the most frequent and included 25 plots (approximately 68.0%). The direct causes of land creep were cutting of foothills, quarrying, land-clearing in mountains, mining exploration, and the creation of burial grounds, all of which added to geological impacts. Among land creeping areas, 27 plots (approximately 73.0%) were the result of man-made activities, and 10 plots (approximately 27.0%) were derived via natural causes such as earthquakes, heavy rainfall, and caving.

• Journal of the Korean Society for Railway
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• v.17 no.4
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• pp.270-280
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• 2014

In this study, to examine the causes of cracks in continuously reinforced concrete tracks (CRCTs) and the main factors affecting cracking, a field survey on the status of cracks and crack patterns in the Gyeong-bu high speed line was conducted, and the crack patterns of CRCT due to the temperature difference between the top of the slab (TCL) and the bottom of the subbase (HSB) and the drying shrinkage of concrete were predicted by a nonlinear finite element model considering the structure of CRCT. The results of the numerical analysis show that cracks will be developed at the interface between the sleeper and the TCL, and under the sleeper due to the temperature difference and concrete shrinkage. This corresponds well to the crack locations found in the field. Also, it is found that the most significant factors are the coefficient of thermal expansion with respect to the temperature difference, and the drying shrinkage strain with respect to shrinkage. According to the results, the reinforcement ratio should be carefully determined considering the structures of CRCT because the crack spacing is not always proportional to the reinforcement ratio due to the sleepers embedded in the TCL.

• Journal of The Geomorphological Association of Korea
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• v.19 no.2
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• pp.51-68
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• 2012

This paper aims to investigate the value in culture, history and ecology of the Mt. Palgong. It attempts to build the strategy for making use of The Mt. Palgong by literature survey, interview, and field survey. The main results are as follows: 1) The boundary of physical geography of the Mt. Palgong is classified into two. The boundary of the Mt. Palgong limits to granite mass block in a narrow sense, while in a broad sense, the boundary of the Mt. Palgong includes a contact aureole to be bordered on the Mt. Palgong granite mass block. The boundary from a cultural viewpoint limits to Daegu city(excluding Dalseong county) and Gyeongsan city, Yeongcheon city, Gunwi county and Chilgok (Dongmyeong-myeon, Giseong-myeon) in Gyeongbuk province. 2) In the geological boundary, one of the south-west slope is clearer than that of the north-east slope of the Mt. Palgong. The landforms such as tor, sheeting joint and gutter are well developed as a whole. Mountain landform such as boulder stream, polygonal cracking is relatively well developed on the south-west slope, while river landform is relatively well developed on the north-east slope of the Mt. Palgong. 3) It is necessary to develope various masterpiece of interesting stories related to Mt. Palgong in order to make the Mt. Palgong excellent tour complex. 4) It is desirable to designate the Mt. Palgong as a national park for systematic management. A master plan should be ultimately designed to raise brand value of Daegu city, and make good identity of the city by restoring 'The Mt. Palgong Jecheondan' and registering 'Gatbawi' as world heritage. 5) It is reasonable that the method of development in The Mt. Palgong should be based on the pattern of 'slow life town'. 'The Mt. Palgong museum' will then be designed to give visitors all the informations on The Mt. Palgong.

• The Korean Journal of Quaternary Research
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• v.16 no.2
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• pp.9-21
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• 2002

In Korea, many open-air upper palaeolithic sites are located at the river valley, particularly exposed in gently rotting terrain along the river course. They are situated at an altitude less trail 30 m above present river bottom, and covered with the blankets of slope deposits of several meters in thickness. The purpose of this research is to eluridate depositional and vegetational environment of the alluvial upper palaeolithic Jangheung-ri sites on the basis of analytical properties of grain size population, chronology, palynology, soil chemistry and clay mineralogy and magnetic susceptibility of the Jangheung-ri Quaternary formations. The lithostratograpy of Jangheung-ri sit is subdivided into 3 layers based on the depositional sequence and radiocarbon ages. From bottom to top, they are composed of slope deposits with lower paleosol layers, young fluvial sand and gravel with backswamp organic muds, and upper paleosol layers. The upper paleosol was formed under rather dry climatic condition between each flooding period. Dessication cracks were prevalent in the soil solum which was filled with secondarily minuted fragments due to pedogenetic process. The soil structure shows typical braided-typed cracks in the root part of cracking texture, and more diversified pattern of crackings downward. The young fluvial sand gravel were formed by rather perennial streams after LGM. The main part of organic muds was particularly formed after 15Ka. Local backswamp were flourished with organic muds and graded suspension materials in the flooding muds were intermittently accumulated in the organic muds until ca. 11Ka. This episode was associated with migration of Nam River toward present course. Organic muds were formed in backswamp or local pond. Abies/Picea-Betula with Ranunculaceae, Compositae, Cyperaceae were prevalent. This period is characterized with B$\Phi$lling, Older Dryas, Allerod, and Younger Dryas (MIS-1). Stone artefacts were found in the lower paleosol layers formed as old as 18Ka-22Ka. Based on the artefacts and landscape settings of the Jangheung-ri site, it is presumed that settlement grounds of old people were buried by frequent floodings of old Nam River, the river-beds of which were heavily fluctuated laterally and river-bed erosions were activated from south to north in Jangheung-ri site until the terminal of LGM9ca 17Ka).

• Korean Journal of Agricultural and Forest Meteorology
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• v.24 no.3
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• pp.145-154
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• 2022

Due to abnormal weather conditions caused by climate change, natural disasters and damages are gradually increasing around the world. Global climate change as accompanied by warming is projected to exert adverse impact on production of potato, which is known as cool season crop. Even though, role of potato as a food security crop is expected to increase in the future, the climate change impacts on potato and adaption strategies are not sufficiently established. Therefore, this study was conducted to analyze the damage pattern of potatoes due to high temperature treatment and to evaluate the response of cultivars. T he high temperature treatment (35~38℃) induced heat stress by sealing the plastic house in midsummer (July), and the quantity and quality characteristics of potatoes were compared with the control group. T otal yield, marketable yield (>80 g) and the number of tubers per plants decreased when heat treatment was performed, and statistical significance was evident. In the heat treatment, 'Jayoung' cultivar suffered a high heat damage with an 84% reduction in yield of >80 g compared to the control group. However, in Jopung cultivar, the decrease was relatively small at 26%. Tuber physiological disturbances (Secondary growth, Tuber cracking, Malformation) tended to increase in the heat stress. Under heat conditions, the tubers were elongated overall, which means that the marketability of potatoes was lowered. T he tuber firmness and dry matter content tended to decrease significantly in the heat-treated group. T herefore, the yield and quality of tubers were damaged when growing potatoes in heat conditions. T he cultivar with high heat adaptability was 'Jopung'. T his result can be used as basic data for potato growers and breeding of heat-resistant cultivars.