• Structural Engineering and Mechanics
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• 제19권5호
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• pp.567-580
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• 2005

Numerous tests on concrete structure members under local pressure demonstrated that the compressive strength of concrete at the loaded surface is increased by the confinement effect provided by the enveloping concrete. Even though most design codes propose specific criteria for preventing bearing failure, they do not take into consideration size effect which is an important phenomenon in the fracture mechanics of concrete/reinforced concrete. In this paper, six series of square prism concrete blocks with three different depths (size range = 1:4) and two different height/depth ratios of 2 and 3 are tested under concentrated load. Ultimate loads obtained from the test results are analysed by means of the modified size effect law (MSEL). Then, a prediction formula, which considers effect of both depth and height on size effect, is proposed. The developed formula is compared with experimental data existing in the literature. It is concluded that the observed size effect is in good agreement with the MSEL.

• Structural Engineering and Mechanics
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• 제72권6호
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• pp.737-746
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• 2019

Concrete mechanical properties change constantly with age, temperature, humidity and the other environmental factors. This research studies the effects of temperature and age on the development of concrete elastic modulus by a series of prism specimens. Elastic modulus test was conducted at various temperatures and ages in the laboratory to examine the effects of temperature and age on it. The experimental results reveal that the concrete elastic modulus decreases with the rise of temperature but increases with age. Then, a temperature coefficient K is proposed to describe the effects of temperature and validated by existing studies. Finally, on the basis of K, analytical models are proposed to determine the elastic modulus of concrete at a given temperature and age. The proposed models can offer designers an approach to obtain more accurate properties of concrete structures through the elastic modulus modification based on actual age and temperature, rather than using a value merely based on laboratory testing.

• Structural Engineering and Mechanics
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• 제80권6호
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• pp.689-699
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• 2021

The present study aims to understand the behaviour of low-strength masonry prisms constructed with locally-produced low-strength hollow concrete blocks. Compression tests were conducted on masonry prisms constructed with three different mortar grades of cement-sand ratios of 1:3, 1:4.5 and 1:6 representing strong, moderately strong and weak mortar. Stress-strain curves were generated from the test results for the masonry prisms. The hollow concrete masonry units employed in this study are some of the weakest as compared to other masonry units employed by other researchers. The compressive strengths for masonry prisms with mortar grades 1:3, 1:4.5 and 1:6 are 2.21 MPa, 2.19 MPa and 2.25 MPa respectively. The results indicate that the masonry compressive strength of such low-strength hollow concrete block masonry prisms is not influenced by the mortar strength. Simple relationships to estimate the modulus of elasticity and compressive strength of masonry prisms is also proposed.

• Advances in concrete construction
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• 제9권3호
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• pp.249-256
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• 2020

This paper aims at investigating the effect of crumb rubber size and content on compressive behaviors of concrete under axial compression. Concrete specimens are designed and produced by replacing natural aggregate with crumb rubber content of 0%, 5%, 10%, 15% and three different sized crumb rubbers (No. 20, No. 40, No. 80 crumb rubber). And the failure mode, compressive strength, elastic modulus, stress-strain curves, peak strain and ultimate strain are experimentally studied. Based on the test results, formulas have been presented to determine the compressive strength, elastic modulus, the relationship between prism compressive strength and cube compressive strength, stress-strain curves and peak strain of crumb rubber concrete (CRC). It is found that the proposed formulas agree well with the test result on the whole, which may be used to practical applications.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2011년도 춘계학술대회 초록집
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• pp.87.2-87.2
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• 2011

1kW급 가정용 연료전지 블로어는 다이어프램방식에 의해 고압 및 일정유량의 가스를 이송시키는 역할을 하고 있다. 본 연구에서는 연료전지 중 연료승압블로어를 대상으로 흡입 및 토출시의 다이어프램 캐비티(Cavity) 내의 공기유동 특성을 수치해석을 적용하여 평가하였다.

• Smart Structures and Systems
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• 제17권1호
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• pp.31-43
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• 2016

Applications of ultrasonic tomography to concrete structures have been reported for many years. However, practical and effective application of this tool for nondestructive assessment of internal concrete condition is hampered by time consuming transducer coupling that limits the amount of ultrasonic data that can be collected. This research aims to deploy recent developments in air-coupled ultrasonic measurements of solids, described in Part 1 of this paper set, to concrete in order to image internal inclusions. Ultrasonic signals are collected from concrete samples using a fully air-coupled (contactless) test configuration. These air coupled data are compared to those collected using partial semi-contact and full-contact test configurations. Two samples are considered: a 150 mm diameter cylinder with an internal circular void and a prism with $300mm{\times}300mm$ square cross-section that contains internal damaged regions and embedded reinforcement. The heterogeneous nature of concrete material structure complicates the application and interpretation of ultrasonic measurements and imaging. Volumetric inclusions within the concrete specimens are identified in the constructed velocity tomograms, but wave scattering at internal interfaces of the concrete disrupts the images. This disruption reduces defect detection accuracy as compared with tomograms built up of data collected from homogeneous solid samples (PVC) that are described in Part 1 of this paper set. Semi-contact measurements provide some improvement in accuracy through higher signal-to-noise ratio while still allowing for reasonably rapid data collection.

• 대한한의학회지
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• 제45권1호
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• pp.139-149
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• 2024

Objectives: The aim of the study was to investigate the potential of Yangdorak diagnosis application against gallstone scanned by Ultrasound diagnosis. Method: For this aim, among 97 patients who had visited Julip Korean Medicine Clinic from July 2016 to June 2023, 30 patients with no gallstone as a control group and 67 patients with gallstone and diagnosed by ultrasonography, were subjected to Yangdorak diagnosis. Then, the changes in Gallbladder Meridian (GB) value as F5 AVE(average of left and right GB value) by Yangdorak were comparatively analyzed between gallstone and non-gallstone groups and statistical significance was evaluated by Tukey's multiple comparison test using Prism software. Results: After all subjects were evaluated by the Yangdorak and ultrasonography to assess the potential of the Yangdorak diagnosis for gallstone, it was noteworthy that the Yangdorak values relevant to F5 AVE of female gallstone group(N=36) were significantly (p<0.001) decreased compared to the control group (N=30), while there was no significance in male gallstone group(N=31). Also, it was recognized significant difference between male and female groups. Conclusion: Based on these results, if the Yangdorak value can be estimated from a decrease with clinical symptom in female patient, it is recommended to follow up the ultrasonography test for diagnosing the gallstone.

• International Journal of Concrete Structures and Materials
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• 제9권4호
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• pp.475-486
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• 2015

Mode II fracture toughness ($K_{IIc}$) of fiber reinforced concrete (FRC) has been widely investigated under various patterns of test specimen geometries. Most of these studies were focused on single type fiber reinforced concrete. There is a lack in such studies for hybrid fiber reinforced concrete. In the current study, an experimental investigation of evaluating mode II fracture toughness ($K_{IIc}$) of hybrid fiber embedded in high strength concrete matrix has been reported. Three different types of fibers; namely steel (S), glass (G), and polypropylene (PP) fibers were mixed together in four hybridization patterns (S/G), (S/PP), (G/PP), (S/G/PP) with constant cumulative volume fraction ($V_f$) of 1.5 %. The concrete matrix properties were kept the same for all hybrid FRC patterns. In an attempt to estimate a fairly accepted value of fracture toughness $K_{IIc}$, four testing geometries and loading types are employed in this investigation. Three different ratios of notch depth to specimen width (a/w) 0.3, 0.4, and 0.5 were implemented in this study. Mode II fracture toughness of concrete $K_{IIc}$ was found to decrease with the increment of a/w ratio for all concretes and test geometries. Mode II fracture toughness $K_{IIc}$ was sensitive to the hybridization patterns of fiber. The (S/PP) hybridization pattern showed higher values than all other patterns, while the (S/G/PP) showed insignificant enhancement on mode II fracture toughness ($K_{IIc}$). The four point shear test set up reflected the lowest values of mode II fracture toughness $K_{IIc}$ of concrete. The non damage defect concept proved that, double edge notch prism test setup is the most reliable test to measure pure mode II of concrete.

• 한국안광학회지
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• 제14권3호
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• pp.59-63
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• 2009

목적: 경기북부 지역 20대 대학생의 근거리 수평사위를 알아보고자 하였다. 방법: 안과적 수술이나 외상과 질병이 없는 평균나이 22.9세 대상자 122명 중 정시안 50명과 비정시안(근시안) 72명을 타각적, 자각적 굴절검사를 통해 원거리 완전교정한 후 Maddox rod를 사용하여 근거리(40 cm) 시의 수평사위를 측정하였다. 결과: Maddox rod를 사용하여 근거리 수평사위를 측정한 결과, 대상자 전체에서 정위 4.9%, 내사위, 9.8% 외사위 85.3%로 나타났으며, 그들중 정시안에서 정위 8%, 내사위 8%, 외사위 84%이었고 비정시안에서는 정위 2.8%, 내사위 11.1%, 외사위 86.1%이었다. 수평사위의 정도는 대상자 전체의 평균 사위정도가 내사위 3.59PD(prism diopter), 외사위 7.04PD이었으며, 정시안에서는 내사위 3.25PD, 외사위 6.60PD이고 비정시안에서는 내사위 3.75PD, 외사위 7.34PD이었다. 결론: 정시안과 비정시안에서의 근거리 수평 사위의 빈도는 정시안에서는 정위가, 비정시안에서는 내사위나 외사위의 빈도가 많으며 특히 비정시안에서의 외사위의 경향이 높게 보였지만 정시안이나 비정시안과 사위와의 관계는 유의성이 없었다(p>0.05). 사위의 정도는 정시안보다 비정시안의 사위정도가 높았다. 여학생보다는 남학생에서 사위정도의 범위가 넓게 나타났다. 또한 굴절이상 정도에 따른 사위정도나 성별에도 통계학적인 유의한 관계가 없었다(p>0.05).

• Journal of Acupuncture Research
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• 제20권1호
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• pp.144-158
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• 2003

This study was carried out to investigate what kinds of statistical techniques have been used to analyze data from oriental medicine research, For study, 551 original articles which used statistical techniques in their data analysis were selected form the articles published in The journal of Korean Acupuncture & Moxibustion Society(JKAMS) between 1984 to 2002. among them, 122 articles used descriptive statistics while 429 articles used inferential statistics for data analysis. For that 429 articles, t-test (189 articles), analysis fo variance (111 articles), chi-square test (14 articles), correlation (10 articles), regression analysis (4 articles), factor analysis(5 articles), or nonparametric test (23 articles) were chose to analyze the data. Nonparametric approach has substantial power in case data do not meet the assumption of normality. This method is not only easy to use ut also provides measures of the statistical variation of nominal and ordinal scale. This study shows that more and more recent papers use nonparametric test compared to the old articles. nine different statistical software or packages (SAS, SPSS, Statview, Minitab, Sigma plot, ISP, Graphpad prism, Excel, Access) have been used in the articles published JKMAS. High level statistical techniques such as SAS, SPSS, and Statview are user friendly and used most for acupuncture and Moxibustion research. Including tables and plots in an article facilitates understanding family process data from a descriptive standpoint, minimized erroneous statistical conclusions, and clarifies theoretically important relationships among variables. Table and plots have been used 500 and 233 articles, respectively. A computer procedure is proposed and illustrated with statistical packages using SAS, SPSS, Statview and ISP.