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 Nbe. 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.