Journal of the Korea Concrete Institute (콘크리트학회논문집)

Korea Concrete Institute (한국콘크리트학회)
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Strengths of Lap Splices Anchored by SD600 Headed Bars

겹침이음 실험을 통한 SD600 확대머리철근의 정착강도 평가

  • Chun, Sung-Chul (Dept. of Architectural Engineering, Mokpo National University) ;
  • Lee, Jin-Gon (Dept. of Architectural Engineering, Mokpo National University)
  • Received : 2012.10.29
  • Accepted : 2013.01.19
  • Published : 2013.04.30
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Abstract

Design provisions for the development length of headed bars in ACI 318-08 include concrete compressive strength and yield strength of headed bars as design parameters but do not consider the effects of transvers reinforcement. In addition, they have very strict limitation for clear spacing and material strengths because these provisions were developed based on limited tests. In this study, splice tests using SD600 headed bars with $2d_b$ clear spacing and transverse reinforcement were conducted. Test results show that unconfined specimens failed due to prying action and bottom cover concrete prematurely spalled. The contribution of head bearing on the anchorage strength is only 15% on average implying that unconfined specimens failed before the head bearing was not sufficiently developed. Confined specimens with stirrups placed along whole splice length have enhanced strengths in bearing as well as bond because the stirrups prevented prying action and improved bond capacity. Bond failure occurred in locally confined specimens where stirrups were placed only at the ends of splice length. The stirrups at ends of splice lengths can prevent prying action but the bond capacity did not increase. From regression analysis of test results, an equation to predict anchorage strength of headed bars was developed. The proposed equation consists of bond and bearing contributions and includes transverse reinforcement index. The average ratio of tests to predictions is 1.0 with coefficient of variation of 6%.

ACI 318-08에 신설된 확대머리 철근의 정착길이 설계식은 콘크리트 강도, 철근 항복강도, 철근 지름만을 변수로 횡보강철근의 영향을 고려하지 않고 있다. 또한 제한적인 데이터에 근거한 설계식으로 순간격과 재료강도에 엄격한 제한을 두고 있다. 이 연구에서는 철근 항복강도 600 MPa의 고강도 철근을 사용하여, $2d_b$의 좁은 순간격을 갖고 횡보강철근을 배근한 겹침 이음 실험을 실시하였다. 실험 결과 횡보강철근을 배근하지 않은 실험체의 경우, 프라잉 거동으로 인해 하부 피복콘크리트가 일찍 탈락되었다. 전체 정착강도 중 확대머리 지압의 기여도는 평균 15%로 지압이 제대로 발현되기 전에 파괴되었다. 이음길이 전체에 스터럽을 배근한 횡보강 실험체는 프라잉 거동이 억제되고 횡보강에 의한 부착강도 증진으로 무보강에 비해 지압과 부착이 모두 증가하였다. 이음 단부에만 횡보강철근을 배근한 단부보강 실험체의 경우, 프라잉 거동은 억제되었지만 이음구간의 부착이 크게 증가되지 않아 지압이 충분히 발현되기 전에 부착에 의해 파괴되었다. 실험결과를 회귀 분석하여 확대머리 철근의 정착강도 평가식을 제안하였다. 평가식은 부착과 지압의 영향을 분리하여 구성하였으며, 콘크리트강도, 횡방향 철근 지수, 정착길이를 설계 변수로 포함하였다. 실험 결과와 비교한 결과 평균 1.0, 변동계수 6%로 변수에 따른 편향 없이 정착강도를 예측하였다.

Keywords

References

  1. Thompson, M. K., Ledesma, A., Jirsa, J. O., and Breen, J. E., "Lap Splices Anchored by Headed Bars," ACI Structural Journal, Vol. 103 No. 2, 2006, pp. 271-279.
  2. ACI Committee 318, Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary, American Concrete Institute, Farmington Hills, Mich., USA, 2008, 465 pp.
  3. Korea Concrete Institute, Concrete Design Code, Kimoondang Publishing Company, Seoul, 2012, pp. 149, 150.
  4. Lee, Y. T., Kim, S. H., Chae, S. H., and Bahn, B. Y., "An Experimetal Study on the Lap Strength of Headed Steel Reinforcements," Journal of the Architectural Institute of Korea, Structure and Construction, Vol. 24, No. 3, 2008, pp. 87-94.
  5. Lee, Y. T., "An Experimental Study on the Lap Splice Performance of Headed Steel Reinforcements with Confinement Details," Journal of the Architectural Institute of Korea, Structure and Construction, Vol. 24, No. 5, 2008, pp. 59-66.
  6. ACI Committee 318, Building Code Requirements for Structural Concrete (ACI 318-11) and Commentary, American Concrete Institute, Farmington Hills, Mich., USA, 2011, 503 pp.
  7. Chun, S. C. and Choi, D. U., "Development and Splice Lengths of FRP Bars with Splitting Failures," Journal of the Korea Concrete Institute, Vol. 22, No. 4, pp. 519-525. (doi: http://dx.doi.org/10.4334/JKCI.2010.22.4.519)
  8. Collins, M. P. and Mitchell, D., Prestressed Concrete Structures, Prentice Hall College Div., 1991.
  9. Thompson, M. K., Jirsa, J. O., and Breen, J. E., "Behavior and Capacity of Headed Reinforcement," ACI Structural Journal, Vol. 103, No. 4, 2006, pp. 522-530.
  10. Furche, J. and Eligehausen, R., "Lateral Blow-Out Failure of Headed Studs Near a Free Edge," Anchors in Concrete- Design and Behavior, SP-130, 1991, American Concrete Institute, Farmington Hills, MI. USA, pp. 235-252.
  11. Korea Concrete Institute, Concrete Design Code and Commentary, Kimoondang Publishing Company, Seoul, 2007, 523 pp.
  12. Orangun, C. O., Jirsa, J. O., and Breen, J. E., "A Reevaluation of Test Data on Developoment Length and Splices," ACI Journal, Proceedings, Vol. 74, No. 3, 1977, pp. 114-122.
  13. ACI Committee 408, Bond and Development of Straight Reinforcing Bars in Tension (ACI 408R-03), ACI, Farmington Hills, Mich., USA, 2003, 49 pp.

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