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Steel and Composite Structures
  Volume 8, Number 6, December 2008, pages 457-473

A critical steel yielding length model for predicting intermediate crack-induced debonding in FRP-strengthened RC members
Jian-Guo Dai, Kent A. Harries and Hiroshi Yokota

    Yielding of the internal steel reinforcement is an important mechanism that influences the Intermediate Crack-induced debonding (IC debonding) behavior in FRP-strengthened RC members since the FRP is required to carry additional forces beyond the condition of steel yielding. However, rational design practice dictates an appropriate limit state is defined when steel yielding is assured prior to FRP debonding. This paper proposes a criterion which correlates the occurrence of IC debonding to the formulation of a critical steel yielding length. Once this length is exceeded the average bond stress in the FRP/concrete interface exceeds its threshold value, which proves to correlate with the average bond resistance in an FRP/concrete joint under simple shear loading. This proposed IC debonding concept is based on traditional sections analysis which is conventionally applied in design practice. Hence complex bond stress-slip analyses are avoided. Furthermore, the proposed model incorporates not only the bond properties of FRP/concrete interface but also the beam geometry, and properties of steel and FRP reinforcement in the analysis of IC debonding strength. Based upon a solid database, the validity of the proposed simple IC debonding criterion is demonstrated.
Key Words
    fiber reinforced plastics; reinforced concrete beams; flexural strengthening; IC debonding
Jian-Guo Dai: Department of Civil and Structural Engineering, The Hong Kong Polytechnic University Hung Hom, Kowloon, Hong Kong
Kent A. Harries : Department of Civil and Environmental Engineering, University of Pittsburgh 936 Benedum Hall, Pittsburgh PA 15261, U.S.A
Hiroshi Yokota : Port and Airport Research Institute, Yokosuka 239-0826, Japan

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