Bond-Strengthening Hooks for RC Members with High Strength Spirals

  • Kim Kil-Hee (Dept. of Architectural Engineering, Kongju National University) ;
  • Sato Yuichi (Dept. of Urban Environment Engineering, Kyoto University)
  • Published : 2005.10.01


This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams and columns. The RC members, which consisted of 1,300 MPa-class spirals as shear reinforcement, often suffered from bond splitting failure. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Twelve specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic and cyclic loading conditions. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective reinforcement ratio $P_{be}$. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. Anchors of the hooks are recommended to be longer than twelve times the hook diameter and inserted deeper than a quarter of the member depth (D/4). Proposed design equations provide modest estimates of the shear strengths.


  1. Sato, Y. et al., 'Buckling of longitudinal bars of RC columns strengthened with continuous fiber sheet', Proceedings of the Japan Concrete Institute, Vol.24, No.3, 2002, pp.2036-2041
  2. AIJ, Recommendation for Detailing and Placing of Concrete Reinforcement, AIJ, 1986, pp.13-17
  3. AIJ, Design Guidelines for Earthquake Resistant Reinforced Concrete Buildings Based on Inelastic Displacement Concept, AIJ, 1999, pp.138-192
  4. CEB-FIP, Model Code for Concrete Structures, CEB-FIP International Recommendations, 3rd edition, Comite EuroInternational du Beton, Paris, 1978, pp.155-160
  5. Kim, K. et al., 'Hook-Shaped Reinforcement for Bond Splitting Prevention in RC Beams', Summaries of Technical Papers of Annual Meeting, AIJ, 2002 C-2, pp.289-292
  6. Sato, Y. and Fujii, S., 'Local stresses and crack displacements in reinforced concrete elements', Journal of Structural Engineering, ASCE, Vol.128, No.10, 2002, pp. 1263-1271
  7. Vecchio, F., J., 'Towards Cyclic Load Modeling of Reinforced Concrete', ACI Structural Journal, Vol. 96, No.2, 1999, pp.193-202

Cited by

  1. Confinement Effect of High-Strength Steel Spirals According to Compressive Strength of Concrete vol.16, pp.4, 2012,
  2. Experimental Study on Improvement of Bond Performance of RC Beams with High-Strength Shear Reinforcement vol.22, pp.4, 2010,