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A Study on Load Bearing Capacity of Composite Member with Steel Rib and Shotcrete in NATM Tunnel (NATM 터널에서 강지보와 숏크리트 합성부재의 하중지지력에 관한 연구)

  • Moon, Sang Hwa;Shin, Young Wan;Kim, Seung Hwan;Yoo, Han Kyu
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.32 no.5C
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    • pp.221-229
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    • 2012
  • Steel ribs such as H-beam or lattice girder are often reinforced to secure the stability of NATM tunnel when the ground is in the bad condition. When designing, however, steel ribs are not often taken into consideration on the numerical analysis when they are regarded as temporary tunnel supports until shotcrete shows its best performance or if they are, there are various modeling methods. This study shows behavior and loading capacity of steel ribs and shotcrete through the strength test on the bending, pressure and full-scaled. Also, we conducted and analyzed the experiment of composite member consisting of shotcrete and steel ribs under the same condition. Through the result, we can find the fact that shotcrete and steel ribs do not work as one unit because of slipping on the boundary. Also, when numerical analyzing, it was concluded that steel ribs cover all bending moment and shotcrete and steel ribs share with axial force according to the compressive strength.

Reliability of Revenue Recognition by Percentage of Completion Method in Construction Industry - Empirical Analysis from Information Perspective (건설업의 공사진행기준에 의한 수익인식의 신뢰성 검증 - 정보적 측면에서의 실증분석)

  • Park, Hong-Jo;Ji, Hyun-Mi
    • Journal of the Korea Institute of Building Construction
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    • v.16 no.5
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    • pp.463-470
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    • 2016
  • Construction companies calculate their revenues and costs from constructing activities using the 'Percentage of Completion Method', which is based on ratio of actual construction cost to total costs estimated. The reliability of the net profit of construction companies is being evaluated lower than other industries due to incorrect application of 'Percentage of Completion Method' to cover losses actually occurred. Therefore, the purpose of this study is to verify the quality of earnings calculated based on 'Percentage of Completion Method' in terms of information usefulness. Results from empirical analysis show that investors in stock market underestimate the value of the construction companies' earning information by applying 'Percentage of Completion Method' and not actively use in investment decision making. Accordingly, it has been confirmed that the association between income information and stock prices falling. These results suggest the need for strict supervision of the supervisory authorities and the practical application of 'Percentage of Completion Method' in reliability.

The implement status of dental hygiene curriculum in Korea and the comparison with the US ADA standard (국내 치위생학 교과목 운영실태 및 미국 치위생학교육 인정평가 기준과의 비교연구)

  • Kim, Sook-Hyang;Kim, Min-Kang;Oh, Sang-Hwan;Mann, Nancy K.
    • Journal of Korean society of Dental Hygiene
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    • v.9 no.3
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    • pp.229-247
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    • 2009
  • The purpose of this study is to provide the improvement basis for Dental Hygiene education program by analyzing the current implement status of Dental Hygiene curriculum in Korea and comparing the status with the US ADA standard. The researcher analyzed the Dental Hygiene syllabus limiting "Dental prophxis", "Comprehensive dental hygiene" subjects only from 31 universities which offer 3 years program. The main interest was to figure the implementing status of the curriculum and to compare the actual teaching content with the CODA 2-17 standard. The results show that there are a number of problems in implementing the Dental Hygiene courses among different universities. First, there is a significant inconsistence among schools in terms of course title, total credit, hours, the ratio for theory and practice, etc. In addition, there is a big gap between the actual content of Dental Hygiene courses and the essential/required content of CODA 2-17 standard. For instance, most of the Dental Hygiene programs in Korea cover the overall assessment stage content and some of implementation stage content. However, very few programs deal with the planning and evaluation stage content. To improve these problematic circumstance a number of suggestions were made. Developing the standardized curriculum for the Dental Hygiene program might be one of the major solutions. Next, the regular accreditation and/or assessment system for the Dental Hygiene program should be developed. This research can provide the basis for the need to assess and improve the Dental Hygiene curriculum.

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Estimation of Carbon Absorption Distribution by Land Use Changes using RS/GIS Method in Green Land (RS/GIS를 이용한 토지이용변화에 의한 녹지의 이산화탄소 (CO2) 흡착량 분포 추정)

  • Na, Sang-Il;Park, Jong-Hwa;Park, Jin-Ki
    • Journal of The Korean Society of Agricultural Engineers
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    • v.52 no.3
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    • pp.39-45
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    • 2010
  • Quantification of carbon absorption and understanding the human induced land use changes (LUC) forms one of the major study with respect to global climatic changes. An attempt study has been made to quantify the carbon absorption by LUC through remote sensing technology. The Landsat imagery four time periods was classified with the hybrid classification method in order to quantify carbon absorption by LUC. Thereafter, for estimating the amount of carbon absorption, the stand biomass of forest was estimated with the total weight, which was the sum of individual tree weight. Individual tree volumes could be estimated with the crown width extracted from digital forest cover type map. In particular, the carbon conversion index and the ratio of the CO2 molecular weight to the C atomic weight, reported in the IPCC guideline, was used to convert the stand biomass into the amount of carbon absorption. Total carbon absorption has been modeled by taking areal estimates of LUC of four time periods and carbon factors for land use type and standing biomass. Results of this study, through LUC suggests that over a period of construction, 7.10 % of forest and 9.43 % of barren were converted into urban. In the conversion process, there has been a loss of 6.66 t/ha/y (7.94 %) of carbon absorption from the study area.

Analysis of Home Economics Textbooks for High School (고등학교 가정 교과서 분석 연구)

  • 윤인경
    • Journal of Korean Home Economics Education Association
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    • v.10 no.2
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    • pp.87-99
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    • 1998
  • The purposes of the study are to see as to how much of changes has occurred in the newly revised high school Home Economics Textbooks required by the 6th Curriculum and to seek future policy directions which can be improved even better, if any, for further revision. To implement this proposal, the study employs 6 different textbooks published in 1996 geared for the 6th Curriculum for data base. The components of the contents divides into two major parts. The first part faUs into a category of holistic analysis of the textbooks, which gives a general perspective of the changes in the textbook revised. It includes those areas of changes in the total number of pacover page, illustrations, table of contents, appendices, unit cover, introductory remarks, summary and evaluation, etc. It also covers the information on authors of textbook. The latter part consists of several specific areas of major changes occurred in the textbooks for the 6th Curriculum. It covers such areas of changes in the composition of category and its weigh laboratory experiences, and illustrations and tables. To conclude the study, there found followings key features : 1) The new textbooks have adopted more of varieties in physical appearances and contents per se as to the older ones. And yet, there still found a weakness in numbers of authors participated to a full reflection of contents variety. In addition, the background of authors reflected on an unrealistic idealism which lacks the on-site information provided by the school teachers. 2) The content area consists of 3 major areas of Human Development & Family Relationship. Food and Nutrition. Clothing and Textiles with ratio of 23.8%, 23.1%, and 21.9% respectively. 3) Human Development & Family Relationship area ranked first with 71 times in the numbers of laboratory activities for each content area. followed by Food and Nutrition with 56 and Family Resorces & Consumerism with 54. These increased numbers of laboratory activities in textbooks represent the changing contents of Home Economics and imply the desirable and positive directions of Home Economics education in Korea. numbers of laboratory activities for each content area. followed by Food and Nutrition with 56 and Family Resorces & Consumerism with 54. These increased numbers of laboratory activities in textbooks represent the changing contents of Home Economics and imply the desirable and positive directions of Home Economics education in Korea.

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Experimental investigation of shear connector behaviour in composite beams with metal decking

  • Qureshi, Jawed;Lam, Dennis
    • Steel and Composite Structures
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    • v.35 no.4
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    • pp.475-494
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    • 2020
  • Presented are experimental results from 24 full-scale push test specimens to study the behaviour of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. The tests use a single-sided horizontal push test setup and are divided into two series. First series contained shear loading only and the second had normal load besides shear load. Four parameters are studied: the effect of wire mesh position and number of its layers, placing a reinforcing bar at the bottom flange of the deck, normal load and its position, and shear stud layout. The results indicate that positioning mesh on top of the deck flange or 30 mm from top of the concrete slab does not affect the stud's strength and ductility. Thus, existing industry practice of locating the mesh at a nominal cover from top of the concrete slab and Eurocode 4 requirement of placing mesh 30 mm below the stud's head are both acceptable. Double mesh layer resulted in 17% increase in stud strength for push tests with single stud per rib. Placing a T16 bar at the bottom of the deck rib did not affect shear stud behaviour. The normal load resulted in 40% and 23% increase in stud strength for single and double studs per rib. Use of studs only in the middle three ribs out of five increased the strength by 23% compared to the layout with studs in first four ribs. Eurocode 4 and Johnson and Yuan equations predicted well the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic experimental load. These equations highly under-estimated the stud capacity, by about 40-50%, for tests with normal load. AISC 360-16 generally over-estimated the stud capacity, except for single stud/rib push tests with normal load. Nellinger equations precisely predicted the stud resistance for push tests with normal load, with ratio of experimental over predicted load as 0.99 and coefficient of variation of about 8%. But, Nellinger method over-estimated the stud capacity by about 20% in push tests with single studs without normal load.

New emerging surface treatment of GFRP Hybrid bar for stronger durability of concrete structures

  • Park, Cheolwoo;Park, Younghwan;Kim, Seungwon;Ju, Minkwan
    • Smart Structures and Systems
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    • v.17 no.4
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    • pp.593-610
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    • 2016
  • In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

Low-Oxygen Atmosphere and its Predictors among Agricultural Shallow Wells in Northern Thailand

  • Wuthichotwanichgij, Gobchok;Geater, Alan F.
    • Safety and Health at Work
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    • v.6 no.1
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    • pp.18-24
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    • 2015
  • Background: In 2006, three farmers died at the bottom of an agricultural shallow well where the atmosphere contained only 6% oxygen. This study aimed to document the variability of levels of oxygen and selected hazardous gases in the atmosphere of wells, and to identify ambient conditions associated with the low-oxygen situation. Methods: A cross-sectional survey, conducted in June 2007 and July 2007, measured the levels of oxygen, carbon monoxide, hydrogen sulfide, and explosive gas (percentage of lower explosive limit) at different depths of the atmosphere inside 253 wells in Kamphaengphet and Phitsanulok provinces. Ambient conditions and well use by farmers were recorded. Carbon dioxide was measured in a subset of wells. Variables independently associated with low-oxygen condition (<19.5%) were identified using multivariate logistic regression. Results: One in five agricultural shallow wells had a low-oxygen status, with oxygen concentration decreasing with increasing depth within the well. The deepest-depth oxygen reading ranged from 0.0% to 20.9%. Low levels of other hazardous gases were detected in a small number of wells. The low-oxygen status was independently associated with the depth of the atmosphere column to the water surface [odds ratio (OR) = 13.5 for 8-11 m vs. <6 m], depth of water (OR = 0.17 for 3-<8 m vs. 0-1 m), well cover (OR = 3.95), time elapsed since the last rainfall (OR = 7.44 for >2 days vs. <1 day), and location of well in sandy soil (OR = 3.72). Among 11 wells tested, carbon dioxide was detected in high concentration (>25,000 ppm) in seven wells with a low oxygen level. Conclusion: Oxygen concentrations in the wells vary widely even within a small area and decrease with increasing depth.

Ambient Air Concentrations of Benzene, Toluene, Ethylbenzene and Xylene in Bangkok, Thailand during April-August in 2007

  • Laowagul, Wanna;Garivait, Hathairatana;Limpaseni, Wongpun;Yoshizumi, Kunio
    • Asian Journal of Atmospheric Environment
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    • v.2 no.1
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    • pp.14-25
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    • 2008
  • Benzene, toluene, ethyl benzene and m-, p-, and o-xylene, the most influential aromatic volatile organic compounds (VOCs), were measured in Bangkok, Thailand, one of the most rapidly developing urban areas in Southern East Asia. The purpose of this study is to characterize the ambient air quality with respect to above mentioned aromatic compounds. The data were monitored in ten sites which cover roadside area, residential area and background area. Canister technique was used to obtain air sample at 24 hour interval per a month during April-August in 2007. GC/MS with three stage preconcentrator was used to analyze these samples. The average concentrations of benzene, toluene, ethyl benzene m-, p-xylene and o-xylene are 5.8, 36.1, 4.1, 11.0 and 3.7μg/m3, respectively. They were observed to be distributed in a log-normal form. Moreover, o-xylene and m, p-xylene exhibited a very good correlation (r=0.976). The slope of the regression equation between them was 3.07 which consisted with a previous reported value. The average ratio of toluene to benzene was 6.4 in April, May June and August. This value was comparable to the ones measured in other Asian cities. Two types of statistical analyses, cluster and factor analyses, were applied to the data in this study. Well characterization was made to understand the air quality of Bangkok area.

Discrete Optimum Design of Reinforced Concrete Beams using Genetic Algorithm (유전알고리즘을 이용한 철근콘크리트보의 이산최적설계)

  • Hong, Ki-Nam;Han, Sang-Hoon
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.9 no.1
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    • pp.259-269
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    • 2005
  • This paper describes the application of genetic algorithm for the discrete optimum design of reinforced concrete continuous beams. The objective is to minimize the total cost of reinforced concrete beams including the costs of concrete, form work, main reinforcement and stirrup. The flexural and shear strength, deflection, crack, spacing of reinforcement, concrete cover, upper-lower bounds on main reinforcement, beam width-depth ratio and anchorage for main reinforcement are considered as the constraints. The width and effective depth of beam and steel area are taken as design variables, and those are selected among the discrete design space which is composed with dimensions and steel area being used from in practice. Optimum result obtained from GA is compared with other literature to verify the validity of GA. To show the applicability and efficiency of GA, it is applied to three and five span reinforced concrete beams satisfying with the Korean standard specifications.