Experimental Study on Bond-Strengthening Hooks for RC Beams

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. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Ten specimens with different numbers and sizes of hooks were prepared to verify the strengthening effectiveness under monotonic four-point loading. The test results indicated that the hooks increased the bond strength along flexural bars although the strengthening effectiveness was limited by the effective number of anchors of hooks N-bc. This limit is determined by the size of the stress-transmitting zones of the concrete around the anchors of the hooks. The bond-strengthening effectiveness of hooks was found to be equivalent to that of conventional internal ties.