• Title, Summary, Keyword: 크리프

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The Effects of Thermal Degradation and Creep Damage on the Microstructure and Composition of the Carbides in the CrMo Steels for Power Plant (발전 설비용 CrMo강의 탄화물 구조와 조성 변화에 미치는 열화 및 크리프 손상의 영향)

  • Ju, Yeon-Jun;Hong, Gyeong-Tae;Lee, Hyeon-Ung;Sin, Dong-Hyeok;Kim, Je-Won
    • Korean Journal of Materials Research
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    • v.9 no.10
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    • pp.1018-1024
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    • 1999
  • The effects of operating temperature and stress on degradation of components in high temperature steam generator were investigated. Several 2.25CrlMo tubes which had operated over 20 years and an unused 9CrlMoVNb tube were tested. For the former samples, the amount of $\textrm{M}_{6}\textrm{C}$ carbide and its size are increased with the aging or operating time. The precipitation behavior of carbides ($\textrm{M}_{2}\textrm{O}$, $\textrm{M}_{6}\textrm{C}$) is changed with the operating temperature of the tubes. However, unused 9CrlMoVNb samples show a different carbide precipitation process due to high chromium, vanadium, and niobium contents. The amount of Cr-rich $\textrm{M}_{23}\textrm{C}_{6}$ carbide is significantly increased with aging time, but that of $\textrm{M}_{6}\textrm{C}$ type carbide is rarely changed with aging time at elevated temperatures.

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Evaluation of Moisture Susceptibility on Asphalt Mixtures mixing Anti-Stripping Agent (박리방지제의 첨가에 따른 아스팔트 혼합물의 수분민감성 평가)

  • Yang, Sung-Lin;Hwang, Sung-Do;Kim, Yeong-Min;Jeong, Kyu-Dong
    • International Journal of Highway Engineering
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    • v.10 no.4
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    • pp.41-52
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    • 2008
  • This study is to evaluate the property for the moisture susceptibility of asphalt mixtures using anti-stripping agent. Asphalt mixtures using lime, hydrated lime and liquid anti-stripping agent are evaluated through the three types of modified moisture conditioning($H_c$, V_s$, F-T). Indirect Tensile Test, that is recommended by AASHTO TP-9, which includes creep test, resilient modulus test and strength test is used to estimate moisture susceptibility. Analysis method through Energy Ratio(ER) that is proposed by Roque at University of Florida is used to evaluate moisture susceptibility and moisture resistance effects of asphalt mixtures using anti-stripping agent. As a test result, material property of asphalt mixtures was changed by moisture conditioning methods and the types of anti-stripping agent. Also, cracking resistance of accumulated moisture damage was changed by moisture conditioning methods and the types of anti-stripping agent. Based on test result, it was found that cracking resistance using Energy Ratio was differed from 10% to 30%.

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The Time Dependent Deflection Characteristics and Evaluation of Reinforced Recycled Aggregate Concrete Beams (순환골재를 사용한 철근콘크리트 보의 장기 처짐 특성 및 평가)

  • Ji, Sang-Kyu;Yun, Hyun-Do;Kim, Sun-Woo;Lee, Eon-Young
    • Journal of the Korea Concrete Institute
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    • v.20 no.1
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    • pp.43-50
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    • 2008
  • This paper presents experimental and analytical results on the long-term behavior of the reinforced recycled aggregate concrete beams under sustained loading. In this experimental program, three beams with different conditions of aggregates replacement (natural aggregate 100%, recycled coarse aggregate 100%, recycled fine aggregate 50%) were subjected to the sustained flexural loading that was a half of the nominal flexural capacity over a period of 1 year. The beam were designed with net span of 2,000 mm and rectangular cross-section of 170 mm width and 170 mm effective depth. The beams were instrumented and monitored to observe the change in the long-term behavior due to creep and shrinkage of concrete under sustained loading. The predictions of long-term deflection by ACI code, Branson, Mayer, Neville, EMM and AEMM were compared with the experimental results. From the experimental results, the reinforced concrete beams with recycled aggregates showed the same performance as that of a beam with natural aggregate. The proposed method to predict the long-term deflections of reinforced recycled aggregate concrete beams gives a good estimation for experimental results.

Development of Three Dimensional Analysis Method of High-Rise Buildings Considering the Construction Sequence and the Inelastic Behavior (시공 단계 및 비탄성거동을 고려한 초고층 건축물의 3차원 해석 기법 개발)

  • Yang, Joo-Kyoung;Seol, Hyun-Cheol;Kim, Jin-Keun
    • Journal of the Korea Concrete Institute
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    • v.20 no.2
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    • pp.249-256
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    • 2008
  • With consideration of the ongoing construction of high-rise buildings, it is becoming increasingly important to be able to accurately predict the behavior of them on the stage of design, construction and service. Even though many researchers have developed the analysis method to predict the behavior of high-rise buildings, their studies were based on the two dimensional frame structures composed of line elements such as beams and columns. Recently the high-rise buildings with flat-plate system is widely used because of its advantages. In this study a three dimensional analysis method is developed to analyze the behavior of the high-rise buildings with flat-plate system since it is difficult to model the structural systems reasonably with the existing two dimensional analysis method. The analysis method considered the construction sequence including the temporary work such as installation of form, removal of form, installation of shore, and removal of shore. Line elements were used to describe columns, beams, and shores and plate elements were used to model slabs. The creep and drying shrinkage of concrete were also considered to account for the inelastic behavior of concrete.

An Experimental Study on the Flexural Behavior of One-Way Concrete Slabs Using the Restorative Mortar and Crimped Wire Mesh (크림프 철망 및 단면복구 보수 모르타르를 사용한 일방향 슬래브의 휨 거동에 관한 실험적 연구)

  • Lee, Mun-Hwan;Song, Tae-Hyeob
    • Journal of the Korea Concrete Institute
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    • v.19 no.5
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    • pp.569-575
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    • 2007
  • The repair of concrete surfaces does not normally take into account structural tolerance for longer service lift and better capabilities of concrete structures. In particular, the repair of surface spelling completes as mortar is applied, which does not display additional structural performances. The use of crimped wire mesh for better construction and fracture resistance, however, expects to have some reinforcement effects. Particularly, it is also expected that the repair of bottom part in structures built between bridges like irrigation structures results in the increase of flexural resistance. Therefore, this study is intended to perform the repair using crimp wire mesh and examine strength depending on the repair section and depth. For this, a slab with 150 mm in depth, 3,000 mm in length and 600 mm in width and total 8 objects to experiment such as upper part, upper whole, bottom part, bottom whole and crimp wire mesh reinforced are manufactured to perform flexural performance. The results of the analysis show that yield strength and failure load increase as the depth of repair materials in the experiment reinforced with crimp wire mesh get bigger. In the same condition, repair of bottom part is able to increase internal force of bending force. Besides, the results show that partial repair of structures under bending force cannot produce flexural performance. Consequently, the repair method with crimp wire mesh results in the increase of flexural resistance.

Evaluation on Laboratory Moisture Damage Characteristics of the Asphalt Mixtures using Indirect Tensile Test (간접인장시험을 이용한 아스팔트 혼합물의 실내 수분손상 특성 평가)

  • Hwang, Sung Do;Rhee, Suk Keun
    • Journal of The Korean Society of Civil Engineers
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    • v.28 no.2D
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    • pp.243-248
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    • 2008
  • Moisture damage of asphalt pavements can usually occur because of the loss of adhesion and cohesion between the asphalt binder and aggregate in the asphalt mixture due to presence of water. And this is one of the causes that is effect on the main distress of asphalt pavement. The objective of this study is to find out moisture damage characteristics of asphalt pavement. Effects of this study changes of the material properties and resistance characteristics of moisture damage on the asphalt mixtures under various temperatures and repeated immersion using indirect tensile test and modify Lottman test were evaluated during this study. The asphalt mixtures were produced using straight asphalt binder, SBS modified asphalt binder and aggregates. The material properties (resilient modulus, indirect tensile strength, failure energy and $DCSE_f$) of the asphalt mixtures were generally decreased with increasing to moisture damage caused by the number of repeated immersion. The decrease ratios of material properties by repeated immersion on SBS modified asphalt mixtures were lower than those of straight asphalt mixtures at all three test temperatures. As a conclusion, current criterion for evaluation moisture damage of asphalt mixtures is difficult for using distinction standard because of the limited evaluation criterion with one time immersion and single material property. Based on this research, to evaluate long term moisture damage on asphalt mixtures, material property tests of various kinds with repeated immersion test are considered.

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Evaluation of Factors Influencing the Dynamic Characteristics of Low Hardness High Damping Rubber Bearings (저경도 고감쇠 고무받침의 동특성에 미치는 영향인자 평가)

  • Choi, Se-Woon;Lim, Hong-Joon;Cho, Hyun-Jin;Park, Kun-Nok;Oh, Ju;Jung, Hie-Young
    • Journal of the Earthquake Engineering Society of Korea
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    • v.12 no.3
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    • pp.11-20
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    • 2008
  • In this paper, the characteristics of low hardness high damping rubber bearings(HDRB) were studied through various prototype tests. The low hardness HDRB were tested to evaluate vertical stiffness, shear stiffness, equivalent damping ratio, various dependencies of shear properties, ultimate shear properties and other factors. The prototype test was performed according to the specifications of ISO 22762-1, and evaluated according to the specifications of ISO 22762-3. The results of the prototype test showed that shear strain and temperature were the factors that most greatly influenced shear stiffness, and that compressive stress was the factor that most greatly influenced the equivalent damping ratio. The frequency dependence test of shear properties showed that two general tendencies of frequency dependence could be observed. At frequencies over 0.1Hz, the changes in shear properties were small. However, at frequencies under 0.1Hz, the changes in shear properties rapidly decreased. The creep test and the ultimate shear test were also performed, and both of them satisfied the requirements of ISO 22762-3.

A Study on the Electron Beam Crosslinking of Acrylic Pressure Sensitive Adhesives for Polarizer Film (전자선 조사를 통한 편광필름용 아크릴계 고분자의 가교화 반응에 대한 연구)

  • Park, Jung-Jin;Choi, Hong-June;Ko, Hwan-Soon;Jeong, Eun-Hwan;Youk, Ji-Ho
    • Polymer Korea
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    • v.36 no.3
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    • pp.344-350
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    • 2012
  • New pressure sensitive adhesives (PSAs) for polarizer film were prepared by electron beam (e-beam) radiation to acrylic copolymers, and their adhesive properties were investigated. The acrylic copolymers were synthesized by free radical polymerization of $n$-butylacrylate (BA), 2-hydroxyethyl methacrylate (HEMA), and acrylic acid (AA). The acrylic copolymers were coated on PET release films to a thickness of 25 ${\mu}m$, laminated to polarizer films, and then radiated with e-beam at room temperature. Gel fractions of all the acrylic copolymers after e-beam radiation at 50 kGy were higher than 93%, and their crosslinking densities were increased with increasing the content of HEMA units. PSA prepared by e-beam radiation of acrylic copolymer synthesized with a feed ratio of BA/HEMA/AA = 89.5/10/0.5 (w/w/w) at a dose of 50 kGy exhibited the best adhesion performances in terms of peel strength, creep resistance, durability and reliability, and light leakage. It is expected that the preparation method of PSAs via e-beam irradiation will improve the producibility and workability of polarizer film for liquid crystal display.

Numerical Evaluation of Stress Loss Rates and Adjusting Coefficients due to Internal and External Constraints of Concrete Long-Term Deformation (콘크리트 장기변형의 내·외부 구속에 의한 응력 손실률 및 수정계수 평가의 전산구조해석)

  • Yon, Jung-Heum;Kim, Hyun-Jin
    • Journal of the Korea Concrete Institute
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    • v.25 no.4
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    • pp.429-438
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    • 2013
  • An object oriented numerical analysis program of axial-flexural elements and the step-by-step method (SSM) has been developed to analyze concrete long-term behaviors of structures constrained internally and externally. The results of the numerical analysis for simple and continuous prestressed (PS) concrete box and composite girders, pre-cast slab of continuous steel composite girder, and simple preflex composite girder show that the adjusting coefficient decreases by increasing constraint. The loss rates of pre-tension force were not sensitive but those of pre-compression force were increased rapidly by decreasing adjusting coefficient. This indicates that the design based on the loss rate of pre-tension can over-estimate the pre-compression force in a concrete section constrained internally and externally. The adjusting coefficients which satisfy results of the numerical analysis are 0.35~0.95, and it can be used as an index of constraint of concrete long-term deformation. The adjusting coefficient 0.5 of Bridge Design Specifications can under-estimate residual stress of PS concrete slab, and the coefficient 0.7 or 0.8 of LRFD Bridge Designing Specifications can under-estimate the loss rates of continuous PS concrete girders. The adjusting coefficient of hybrid structures should be less then 0.4.

Evaluation of Loss of Prestress Force of Tensile Anchor by Long Term Measurement (장기계측을 통한 인장형 앵커의 인장력 손실 평가)

  • Lee, Bongjik;Lee, Jongkyu
    • Journal of the Korean Geoenvironmental Society
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    • v.16 no.10
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    • pp.15-22
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    • 2015
  • In this study, to evaluate the long-term behavior characteristics and the loss of prestress force, the long-term measurement of the tensile anchors in the actual construction was performed and the results were analyzed comparing with the existing estimation. As the reinforcement member used for the purpose of slope stability or uplift-resisting of the permanent structure, etc, the permanent anchor should maintain the functions during the performance period of the structure differently from the temporary anchor. However, as the time passes by, since the relaxation and the creep of the anchor occur constantly, the management for the loss of tensile force is essential to perform the functions stably. So far, the loss of the tensile force has been estimated according to the reduction of the prestress using elasticity theory and using the relaxation value according to the type of tension member and the test using the long-term measurement is limited. Therefore, in this study, the site condition and the ground were investigated for the tensile anchor in the actual construction and the long-term measurement results more than 500 days was analyzed by installing the loadcell, inclinometer and the groundwater level gauge. In addition, the long-term behavior characteristics were evaluated by comparing the disposition of the measured earth retaining wall and the tension force loss of the anchor with the existing interpretation results. In the evaluation results, the most of the tension force loss occurs within 90 days and the loss was measured less than the estimated values.