• Title/Summary/Keyword: 배면박리한계두께

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Prediction of Scabbing Limit Thickness Considering Fiber Reinforced Effect about High-Velocity Impact (고속비상체 충돌에 대한 섬유보강효과를 고려한 배면박리한계두께 예측)

  • Kim, Jung-Hyun;Kim, Gyu-Yong;Kim, Hong-Seop;Yoon, Min-Ho;Han, Sang-Hyu;Kim, Rae-Hwan
    • Proceedings of the Korean Institute of Building Construction Conference
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    • 2014.11a
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    • pp.30-31
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    • 2014
  • Since consists of regression equation by penetration depth prediction calculated by existing NDRC formula mainly considers properties of projectile, impact velocity, compressive strength as parameter, it is difficult to apply it to fire reinforced concrete. In this study, scabbing limit thickness was predict considering fiber reinforcement effect by local fracture of concrete was evaluated through high-velocity impact test. As a result of applying fracture reduction coefficient to NDRC, it was possible to predict scabbing limit thickness of fiber reinforced concrete similarly with actual measurement.

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Evaluation on Rear Fracture Reduction and Crack Properties of Cement Composites with High-Velocity Projectile Impact by Fiber Types (섬유 종류에 따른 시멘트복합체의 고속 비상체 충격에 대한 배면파괴저감 및 균열특성 평가)

  • Han, Sang-Hyu;Kim, Gyu-Yong;Kim, Hong-Seop;Kim, Jung-Hyun;Nam, Jeong-Soo
    • Journal of the Korea Concrete Institute
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    • v.27 no.2
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    • pp.157-167
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    • 2015
  • Cement composites subjected to high-velocity projectile shows local failure and it can be suppressed by improvement of flexural toughness with reinforcement of fiber. Therefore, researches on impact resistance performance of cement composites are in progress and a number of types of fiber reinforcement are being developed. Since bonding properties of fiber with matrix, specific surface area and numbers of fiber are different by fiber reinforcement type, mechanical properties of fiber reinforced cement composites and improvement of impact resistance performance need to be considered. In this study, improvement of flexural toughness and failure reduction effect by impact of high-velocity projectile have been evaluated according to fiber type by mixing steel fiber, polyamide, nylon and polyethylene which are have different shape and mechanical properties. As results, flexural toughness was improved by redistribution of stress and crack prevention with bridge effect of reinforced fibers, and scabbing by high-velocity impact was suppressed. Since it is possible to decrease scabbing limit thickness from impact energy, thickness can be thinner when it is applied to protection. Scabbing of steel fiber reinforced cement composites was occurred and it was observed that desquamation of partial fragment was suppressed by adhesion between fiber and matrix. Scabbing by high-velocity impact of synthetic fiber reinforced cement composites was decreased by microcrack, impact wave neutralization and energy dispersion with a large number of fibers.

Fracture Property of Concrete on Spherical and Flat Nose Shape Projectile Impact (반구형과 평탄형 선단 비상체의 충돌을 받는 콘크리트의 파괴특성)

  • Lee, Sang-Kyu;Kim, Gyu-Yong;Kim, Hong-Seop;Son, Min-Jae;Nam, Jeong-Soo
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.20 no.6
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    • pp.98-105
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    • 2016
  • In this study, projectiles with 2 kinds of nose shape: spherical and flat were impacted into normal concrete and fiber reinforced concrete panels. The fracture depth and form, crater diameter, tensile strain at rear face were evaluated. It was confirmed that smaller projectile nose areas resulted in deeper penetrations associated with concentrated impact forces and small front-face crater diameters in impact test. Conversely, larger projectile nose areas resulted in shallower penetrations and larger front-face fracture diameters. Similar front-face failure and strain distribution relationships based on the projectile nose shape were observed for normal and fiber-reinforced concrete although the rear-face tensile strain and scabbing were significantly reduced by the fiber reinforcement. In addition, a direct relationship was confirmed between the penetration depth based on the projectile nose shape and the tensile strain on the rear face. Thus the impact strain behavior is required to predict the scabbing behavior with penetration depth.

Evaluation of Protective Performance of Fiber Reinforced Concrete T-Wall (섬유보강 콘크리트 방호벽의 방호성능 향상 검토)

  • Lee, In-Cheol;Kim, Hong-Seop;Nam, Jeong-Soo;Kim, Suk-Bong;Kim, Gyu-Yong
    • Journal of the Korea Institute of Building Construction
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    • v.13 no.5
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    • pp.465-473
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    • 2013
  • Concrete is an outstanding material in terms of its impact and blast resistance performance. However, there a limitation of concrete is its risk of collapse due to the brittle failure and spalling. Increasing the thickness of members was used as a method to enhance the protective performance of concrete, despite the resulting inefficient space. To solve this problem, different types of fiber reinforced concrete were developed. Recently, another type of fiber reinforced concrete is also being developed and applied as a material that offers protection against impacts and blasts by increasing the flexural toughness of concrete. In this study, the test was conducted to evaluate the impact resistance performance of fiber reinforced concrete and mortar according to impact of high-velocity projectile. A concrete T-wall was also tested to evaluate its protective performance from fragment by 155mm-thick artillery shell. The test results revealed that improving flexural strength through fiber reinforcement inhibited cracks and spalling of rear, and spalling of front by high-velocity impact. As such, it is expected to improve the protective performance of the T-wall and reduce the thickness of the member.

Impact Resistance of Steel Fiber-Reinforced Concrete Panels Under High Velocity Impact-Load (고속충격하중을 받는 강섬유보강콘크리트 패널의 내충격성능)

  • Kim, Sang-Hee;Kang, Thomas H.K.;Hong, Sung-Gul;Kim, Gyu-Yong;Yun, Hyun-Do
    • Journal of the Korea Concrete Institute
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    • v.26 no.6
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    • pp.731-739
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    • 2014
  • This paper describes the evaluation of the impact performance of steel fiber-reinforced concrete based on high-velocity impact experiments using hard spherical balls. In this experimental study, panel specimens with panel thickness to ball diameter (h/d) ratios of 3.5 or less were tested with variables of steel fiber volume fraction, panel thickness, impact velocity, and aggregate size. Test results were compared with each other to evaluate the impact resistance. The results showed that the percentage of weight and surface loss decreased as the steel volume fraction increased. However, the penetration depth increased with up to steel fiber volume fraction of 1.5%. Particularly the results of specimens with 20 mm aggregates showed poorer performance than those with 8 mm aggregates. The results also confirmed that the impact performance prediction formulas are conservative with (h/d) ratios of 3.5 or less. Despite the conservative predictions, the modified NDRC formula and ACE formula predict the impact performance more consistently than the Hughes formula.