Flexure tests on narrow concrete beams strengthened with CFRP sheets end-locked by winding around twin-rods

In order to prevent the debonding failure occurring in reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) sheets, a technique of self-locking anchorage which anchors the ends of CFRP strips by winding around twin rods in parallel in a particular way was invented. In view of the limited width of a narrow beam, a scheme with side anchorage and bottom bonding was proposed, i.e., placing the CFRP to the beam bottom and using bolts to fix the double L-shaped end device with twin rods to the beam side. Five rectangular beams with lower concrete strength were tested in four-point bending, including four beams strengthened in flexure by using above self-locking anchorage method. The feasibility of the new scheme was validated and the influence of the strip width and whether it is bonded with the bottom of beam were studied. The test results show that the strengthening method in this paper can avoid the end-debonding, and the strip can still carry large tension even when the intermediate debonding happens, or in the late loading stage of unbonded strengthened beams. Therefore, the ultimate load is obviously promoted as compared with the control beam. Comparatively, the specimens with bonded strips perform better than that with unbonded, and increasing the strip width is beneficial to enhancing the load bearing capacity of beams.