• Title/Summary/Keyword: 인장.전단강도

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A Study on the Performance Evaluation Method of Warm-mix Asphalt Mixture by the Analysis of Bonding Properties between Asphalt Binder and Aggregate (중온 아스팔트 혼합물의 성능 평가를 위한 아스팔트 바인더와 골재 사이의 접착물성분석 방법에 관한 연구)

  • Yoo, In Sang;Cho, Dong-Woo;Hwang, Sung Do;Rhee, Suk Keun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.31 no.6D
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    • pp.803-810
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    • 2011
  • The public interest of global warming and energy shortage is gradually increased, and the related industries also have become interested in developing eco-friendly material and technology. Warm-mix asphalt (WMA) is a result of the developments to alleviate global warming and energy problems. This WMA is produced at lower temperatures than the temperature at which hot mix asphalt (HMA) is produced. Because most tests in Superpave are developed only for the performance and maintenance of HMA produced by hot temperatures, it is difficult for the tests to identify properly the material properties and then evaluate the performances between HMA and WMA. This study deals with the development of a new protocol to differentiate HMA and WMA performance, and especially the interfacial properties between asphalt and aggregate are targeted as the performance indicator; thus, an evaluation method and guideline are suggested. The concept and idea of the test method applied in this study were modified from the DSR moisture damage test protocol. In addition, TSR test was performed to affirm the relation between the asphalt-aggregate interface and the asphalt-aggregate mixture performances. The followings are the results of this study. Shear stress at 85% linear visco-elastic complex modulus (LVE $G^*$) can be a better parameter than LVE $G^*$, which can assess the interfacial or bonding performance between asphalt and aggregate. Moreover, measuring the bonding performance in thinner film thicknesses will be a better way to evaluate the real and field situation between asphalt and aggregate. The interfacial properties' criteria to apply the newly developed test and parameter should be developed, after the asphalt mixture criteria relating to the interfacial properties are completed.

Non-linear Time History Analysis of Piloti-Type High-rise RC Buildings (필로티형 고층 RC건물의 비선형시간이력해석)

  • Ko, Dong-Woo;Lee, Han-Seon
    • Journal of the Earthquake Engineering Society of Korea
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    • v.13 no.1
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    • pp.35-43
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    • 2009
  • Two types of piloti-type high-rise RC building structures having irregularity in the lower two stories were selected as prototypes, and nonlinear time history analysis was performed using OpenSees to verify the analysis technique and to investigate the seismic capacity of those buildings. One of the buildings studied had a symmetrical moment-resisting frame (BF), while the other had an infilled shear wall in only one of the exterior frames (ESW). A fiber model, consisting of concrete and reinforcing bar represented from the stress-strain relationship, was adapted and used to simulate the nonlinearity of members, and MVLEM (Multi Vertical Linear Element Model) was used to simulate the behavior of the wall. The analytical results simulate the behavior of piloti-type high-rise RC building structures well, including the stiffness and yield force of piloti stories, the rocking behavior of the upper structure and the variation of the axial stiffness of the column due to variation in loading condition. However, MVLEM has a limitation in simulating the abrupt increasing lateral stiffness of a wall, due to the torsional mode behavior of the building. The design force obtained from a nonlinear time history analysis was shown to be about $20{\sim}30%$ smaller than that obtained in the experiment. For this reason, further research is required to match the analytical results with real structures, in order to use nonlinear time history analysis in designing a piloti-type high-rise RC building.

Study on the Durability of Composite Tilting Pad Journal Bearing for Turbo Compressor System under Oil-cut Situation (터보 컴프레셔용 복합재료 틸팅 패드 저널 베어링의 오일 공급 중단 상황에서의 내구성 연구)

  • Choe, Kang-Yeong;Jung, Min-Hye;You, Jun-Il;Song, Seung-A;Kim, Seong-Su
    • Composites Research
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    • v.29 no.3
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    • pp.111-116
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    • 2016
  • The tilting pad journal bearing for the turbo compressor application has a role to support high speed and heavy loading rotor. White metal has been widely used for the bearing material but the conventional bearing is immediately suspended and induces serious serious damage to the rotor under the unexpected oil cut situation or the insufficient oil film formation. The carbon fiber reinforced composite having high specific stiffness, specific strength and excellent tribological characteristics can solve these seizure problems. In this work, the study on the durability of high thermal resistance carbon fiber/epoxy composite tilting pad journal bearing under oil cut situation was conducted. The material properties of the composite materials including tensile, compressive and interlaminar properties were measured at room and high temperature of oil cut situation. To investigate the possibility of failure of composite tilting pad journal bearing under oil cut situation, the stress distribution of the composite bearing was analyzed via finite element analysis and the Tsai-Wu Failure index was calculated. To verify the failure analysis results, the oil cut tests for the composite tilting pad journal bearing were conducted using industrial test bench.

A Study on the Evaluation Method to Flexural-bonding Behavior of FRP-Rebar Concrete Member (FRP를 보강근으로 사용한 콘크리트 부재의 휨-부착 거동 평가방법에 관한 연구)

  • Choi, So-Yoeng;Choi, Myoung-Sung;Kim, Il-Sun;Yang, Eun-Ik
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.25 no.5
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    • pp.149-156
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    • 2021
  • FRP has been proposed to replace the steel as a reinforcement in the concrete structures for addressing the corrosion issue. However, FRP-Rebar does not behave in the same manner as steel because the properties of FRP are different. For example, FRP-Rebar has a high tensile strength, low stiffness, and linear elastic behavior which results in a difference bonding mechanism to transfer the load between the reinforcement and the surrounding concrete. Therefore, bonding behavior between FRP-Rebar and concrete has to be investigated using the bonding test. So, Pull-out test has been used to estimate bond behavior because it is simple. However, the results of pull-out test have a difference with flexural-boding behavior of FRP-Rebar concrete member. So, it is needed to evaluate the real fleuxral-bonding behavior. In this study, the evaluation method to flexural-bonding behavior of FRP-Rebar concrete member was reviewed and compared. It was found that the most accurate evaluation method for the fleuxral-bonding behavior of FRP-Rebar concrete member was splice beam test, however, the size and length of specimen have to increase than other test method and the design and analysis of splice beam is complex. Meanwhile, characteristics of concrete could be reflected by using arched beam test, unlike hinged beam test which is based on the ignored change of moment arm length in equilibrium equation. However, the possibility of shear failure exists before the flexural-bonding failure occur.

Anatomical and Physical Properties of Pitch Pine (Pinus rigida Miller) - The Characteristics of Stem, Branch, Root and Topwood - (리기다소나무(Pinus rigida Miller)의 목재해부학적(木材解剖學的) 및 물리학적성질(物理學的性質)에 관(關)한 연구(硏究) - 간(幹), 지(枝), 근(根), 초두목(梢頭木)의 특성(特性)을 중심(中心)으로 -)

  • Lee, Phil Woo
    • Journal of Korean Society of Forest Science
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    • v.16 no.1
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    • pp.33-62
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    • 1972
  • Pitch pine (Pinus rigida Miller) in Korea has become one of the major silvicultural species for many years since it was introduced from the United States of America in 1907. To attain the more rational wood utilization basical researches on wood properties are primarily needed, since large scale of timber production from Pitch Pine trees has now been accomplishing in the forested areast hroughout the country. Under the circumustances, this experiment was carried out to study the wood anatomical, physical and mechanical properties of Pitch Pine grown in the country. Materials used in this study had been prepared by cutting the selected pitch pine trees from the Seoul National University Forests located in Suwon. To obtain and compare the anatomical and physical properties of the different parts of tree such as stem, branch, top and rootwood, this study had been divided into two categories (anatomical and physical). For the anatomical study macroscopical and microscopical features such as annual ring, intercellular cannal, ray, tracheid, ray trachid, ray parenchyma cell and pit etc. were observed and measured by the different parts (stem, branch, root and topwood) of tree. For the physical and mechanical properties the moisture content of geen wood, wood specific gravity, shrinkage, compression parallel to the grain, tension parallel and perpendicular to the grain, radial and tangential shear, bending, cleavage and hardness wree tested. According to the results this study may be concluded as follows: 1. The most important comparable features in general properties of wood among the different parts of tree were distinctness and width of annual ring, transition from spring to summerwood, wood color, odor and grain etc. In microscopical features the sizes of structural elements of wood were comparable features among the parts of tree. Among their features, length, width and thickness of tracheids, resin ducts and ray structures were most important. 2. In microscopical features among the different parts of tree stem and topwood were shown simillar reults in tissues. However in rootwood compared with other parts on the tangential surface distinctly larger ray structures were observed and measured. The maximum size of unseriate ray was attained to 27 cell ($550{\mu}$) height in length and 35 microns in width. Fusiform rays were formed occasionally the connected ray which contain one or several horizontal cannals. Branchwood was shown the same features like stemwood but the measured values were very low in comparing with other parts of tree. 3. Trachid length measured among the different parts of tree were shown largest in stem and shortest in branchwood. In comparing the tracheid length among the parts the differences were not shown only between stem and rootwood, but shown between all other parts of tree. Trachid diameters were shown widest in rootwood and narrowest in branchwood, and the differences among the different parts were not realized. Wall thickness were shown largest value in rootwood and smallest in branchwood, and the differences were shown between root and top or branchwood, and between stem and branch or top wood, but not shown between other parts of tree. 4. Moisture contents of green wood were shown highest in topwood and lowest in heartwood of stem. The differences among the different parts were recognized between top or heartwood and other parts of tree, but not between root and branchwood or root and sapwood. 5. Wood specific gravities were shown highest in stem and next order root and branchwood, but lowest in topwood. The differences were shown clearly between stemwood and other parts of tree, but not root and branchwood. However the significant difference is realized as most lowest value in topwood. 6. In compression strength parallel to the grain compared among the different parts of tree at the 14 percent of moisture content, highest strength was appeared in stem, next order branch and rootwood, but lowest in topwood. 7. In bending strength compared among the different parts of tree at the 14 percent of moisture content clearly highest strength was shown in branchwood, next order stem and root, but lowest in topwood. Though the branchwood has lower specific gravity than stemwood it was shown clearly high bending strength.

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Nondestructive Evaluation and Microfailure Mechanisms of Single Fibers/Brittle Cement Matrix Composites using Electro-Micromechanical Technique and Acoustic Emission (Electro-Micromechanical 시험법과 Acoustic Emission을 이용한 단섬유/시멘트 복합재료의 미세파괴 메커니즘과 비파괴적 평가)

  • 박종만;이상일;김진원;윤동진
    • Composites Research
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    • v.14 no.3
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    • pp.18-31
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    • 2001
  • Interfacial and microfailure properties of the modified steel, carbon and glass fibers/cement composites were investigated using electro-pullout test under tensile and compressive tests with acoustic emission (AE). The hand-sanded steel composite exhibited higher interfacial shear strength (IFSS) than the untreated and even neoalkoxy zirconate (Zr) treated steel fiber composites. This might be due to the enhanced mechanical interlocking, compared to possible hydrogen or covalent bonds. During curing process, the contact resistivity decreased rapidly at the initial stage and then showed a level-off. Comparing to the untreated case, the contact resistivity of either Zr-treated or hand-sanded steel fiber composites increased to the infinity at latter stage. The number of AE signals of hand-sanded steel fiber composite was much more than those of the untreated and Zr-treated cases due to many interlayer failure signals. AE waveforms for pullout and frictional signals of the hand-sanded composite are larger than those of the untreated case. For dual matrix composite (DMC), AE energy and waveform under compressive loading were much higher and larger than those under tensile loading, due to brittle but well-enduring ceramic nature against compressive stress. Vertical multicrack exhibits fur glass fiber composite under tensile test, whereas buckling failure appeared under compressive loading. Electro-micromechanical technique with AE can be used as an efficient nondestructive (NDT) method to evaluate the interfacial and microfailure mechanisms for conductive fibers/brittle and nontransparent cement composites.

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Characterization of Thermal Degradation of Polymide 66 Composite: Relationship between Lifetime Prediction and Activation Energy (폴리아미드 66 복합소재의 열 열화 특성: 수명 예측과 활성화 에너지의 상관관계)

  • Jung, Won-Young;Weon, Jong-Il
    • Polymer(Korea)
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    • v.36 no.6
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    • pp.712-720
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    • 2012
  • Thermal degradation for glass fiber-reinforced polyamide 66 composite (PA 66) with respect of thermal exposure time has been investigated using optical microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. As the thermal exposure time was prolonged, a slight increase in tensile strength for only initial stage and afterward, a proportional decrease of tensile strength was observed. These results can be explained by the increase of crystallinity, followed by the increase of crosslinking density, chain scission and the decrease in chain mobility, due to thermal oxidation with the exposure time. Fourier transform infrared spectroscopy results showed the increase of ketone peak and silica peak on the surface of thermally exposed PA 66. In addition, the thermal decomposition kinetics of PA 66 was analyzed using thermogravimetric analysis at three different heating rates. The relationship between activation energy and lifetime-prediction of PA 66 was investigated by several methodologies, such as statistical tool, UL 746B, Ozawa and Kissinger. The activation energy determined by thermogravimetric analysis had a relatively large value compared with that from the accelerated test. This may result in over-estimating the lifetime of PA 66. In this study, a master curve of exponential fitting has been developed to extrapolate the activation energy at various service temperatures.

Design Considerations and Pull-Out Behavior of Mechanical Anchor of Reinforcement (철근 기계적 정착장치의 설계 고려사항과 인발특성)

  • 천성철;김대영
    • Journal of the Korea Concrete Institute
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    • v.13 no.6
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    • pp.593-601
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    • 2001
  • In RC structure, sufficient anchorage of reinforcement is necessary for the member to produce the full strength. Generally, conventional standard hook is used for the reinforcement's anchorage. However, the use of standard hook results in steel congestion, making fabrication and construction difficult. Mechanical anchor offers a potential solution to these problems and may also ease fabrication, construction and concrete placement. In this paper, the required characteristics and the design considerations of mechanical anchor were studied. Also, the mechanical anchor was designed according to the requirements. To investigate the pull-out behavior and properness of mechanical anchorage, pull-out tests were performed. The parameters of tests were embedment length, diameter of reinforcement, concrete compressive strength, and spacing of reinforcements. The strengths of mechanical anchor were consistent with the predictions by CCD method. The slip between mechanical anchor and concrete could be controlled under 0.2mm. Therefore, the mechanical anchor with adequate embedment could be used for reinforcement's anchorage. However, it was observed that the strength of mechanical anchors with short spacing of reinforcements was greatly reduced. To apply the mechanical anchor in practice (e.g. anchorage of the beams reinforcements in beam-column joint), other effects that affect the mechanical anchor mechanism, such as confinement effect of adjacent member from frame action or effects of shear reinforcement, should be considered.

Ground Test & Evaluation of Conformal Load-bearing Antenna Structure for Communication and Navigation (통신 항법용 다중대역 안테나 내장 스킨구조의 지상시험평가)

  • Kim, Min-Sung;Park, Chan-Yik;Cho, Chang-Min;Jun, Seung-Moon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.41 no.11
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    • pp.891-899
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    • 2013
  • This paper suggests a test and evaluation procedure of conformal load-bearing antenna structure(CLAS) for high speed military jet application. A log periodic patch type antenna was designed for multi-band communication and navigation antenna. Carbon/Glass fiber reinforced polymer was used as a structure supporting aerodynamic loads and honeycomb layer was used to improve antenna performance. Multi-layers were stacked and cured in a hot temperature oven. Gain, VSWR and polarization pattern of CLAS were measured using anechoic chamber within 0.15~2.0 GHz frequency range. Tension, shear, fatigue and impact load test were performed to evaluate structural strength of CLAS. Antenna performance test after every structural strength test was conducted to check the effect of structural test to antenna performance. After the application of new test and evaluation procedure to validate a new CLAS, a design improvement was found.

Inelastic Behavior of Post-tensioned Wide Beam System with different Reinforcement ratios within Column core (포스트텐션을 도입한 넓은 보에서 기둥 폭 내부에 배근된 보강재의 정착비에 따른 비탄성 거동 평가)

  • Choi Yun-Cheul;Lim Jae-Hyung;Moon Jeong-Ho;Lee Li-Hyung;Kwon Ki-Hyuk
    • Journal of the Korea Concrete Institute
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    • v.17 no.1 s.85
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    • pp.85-94
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    • 2005
  • Post-tensioned Precast concrete System(PPS) consists of U-shaped precast wide beams and concrete column. The continuity of beam-column joint is provided with floor concrete cast on the PC shell beam and post-tensioning. The purpose of this paper is to evaluate the response of PPS interior beam-column joint subjected to cyclic lateral loading. To this end, an experimental investigation was performed with three half-scale specimens of interior connection. The design parameters are the amount of beam reinforcement placed inside the joint core. The test results showed that cracks were distributed well without my significant degradation of strength and ductility. Also, it was found that the prestressing may affect to alter the torsional crack angle. And the specimens sufficiently resist up to limiting drift ratio of 0.035 in accordance with the provisional by ACl of acceptance criteria for concrete special moment frames.