Bond-Strengthening Hooks for RC Members with 1300 MPa-Class Shear-Reinforcing Spirals

Part II: Shear Strength Estimation Based on the BCJ-C1166 Guideline

抄録

This paper presents experimental investigations of a bond-strengthening method for reinforced concrete (RC) beams and columns, which consist of 1300 MPa-class spirals as shear reinforcement. This method uses U-shaped bars (hooks) made of normal strength steel. The hooks are applied to longitudinal bars as supplemental lateral reinforcement. The hooks increased the bond strength along longitudinal bars, resulting in a remarkable improvement in the members' shear capacity.
Experimental observation indicated that a hook′s anchor requires a stress-transmitting zone in the concrete within 15 times the hook diameter. Based on this observation, the authors proposed limiting the bond-strengthening effectiveness by introducing an effective number of hook anchors N_be. The AIJ Guideline-based equations were used to rationally evaluate the shear capacities of the members.
When the 1300 MPa-class spirals are adopted in constructing RC buildings, however, structural designers prefer to design with a guideline evaluated by the Building Center of Japan (BCJ-C1166) than with the AIJ Guideline because the latter underestimates the effectiveness of the spiral. Hence, this paper extends the BCJ Guideline to estimate the shear capacities of RC members with hooks. The extended guideline was corroborated with the test results of 28 specimens.