• Title/Summary/Keyword: 비틀림 횟수

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Influence of Number of Twist on Tensile Behavior of High Performance Fiber Reinforced Cementitious Composites with Twisted Steel Fibers (비틀림 강섬유의 비틀림 횟수가 고성능 섬유보강 시멘트 복합재료의 인장거동에 미치는 영향)

  • Kim, Dong-Joo
    • Journal of the Korea Concrete Institute
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    • v.22 no.4
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    • pp.575-583
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    • 2010
  • This research investigated the influence of the number of twist on single fiber pullout behavior of Twisted steel (T-) fiber and tensile behavior of high performance cementitious composites reinforced with the (T-) fibers (HPFRCC). Micromechanical pullout model for T- fibers has been applied to analytically investigate the influence of various fiber parameters including the number of twist on single fiber pullout behavior; and, to optimize the number of twist to generate larger pullout energy during fiber pullout without fiber breakage. In addition, an experimental program including single fiber pullout and tensile tests has been performed to investigate the influence of twist ratio experimentally. Two types of T- fiber with different twisted ratios, T(L)- fiber (6ribs/30 mm) and T(H)- fiber (18ribs/30 mm), were tested. T(L)- fiber produced higher equivalent bond strength (larger pullout energy) although T(H)- fiber produced higher pullout stress during pullout since T(H)- fiber showed fiber breakage during pullout. Tensile test results confirmed that T(L)- fiber in high strength mortar generates better tensile performance of HPFRCC, e.g., load carrying capacity, strain capacity and multiple micro-cracking behavior.

Development of Permanent Deformation Prediction Model for Trackbed Foundation Materials based on Shear Strength Parameters (강화노반 쇄석재료의 전단강도특성을 고려한 영구변형예측모델 개발)

  • Lim, Yujin;Hwang, Jungkyu;Cho, Hojin
    • Journal of the Korean Society for Railway
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    • v.15 no.6
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    • pp.623-630
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    • 2012
  • Formation used as trackbed foundation for providing vertical bearing capacity onto rail foundation are composed of crushed stones usually with certain type of grain size distribution. Permanent deformation in trackbed foundation can be generated by increasing number of load repetition due to train traffic increases, causing track irregularity. In this study, a specially prepared trackbed foundation materials (M-40) used in Korea has been tested using a large repetitive triaxial compression apparatus in order to understand resilient and permanent deformation characteristics of the material. From these test results, resilient and permanent deformation characteristic are analyzed so that a permanent deformation model is developed which can consider number of load repetition N, confining stress (${\sigma}_3$), shear stress ratio(${\tau}/{\tau}_f$) and stiffness of the material.