Experimental study on the flexural strengthening of one-way RC slabs with end-buckled and/or externally bonded CFRP sheets

Reinforced concrete (RC) slabs are widely strengthened in flexure by externally bonding (EB) carbon-fiberreinforced polymer (CFRP) sheets, where debonding failure remains a critical issue. To solve the debonding problems, a self-locking device is initially proposed to enhance the anchorage at the end of FRP sheets for strengthening of RC slabs in this study. The effects on the debonding resistance and the improvement of the strengthening efficiency are experimentally investigated. Six one-way RC slabs strengthened with end-buckled and/or externally bonded CFRP sheets were prepared for the four-point bending tests. All strengthened specimens had higher ultimate loads than the reference specimen. While the slab strengthened by EB CFRP had a limited increase in ultimate load, the improvement was significant for the cases with hybrid anchored (HA) CFRP including both end-anchorage and external bonding, which was 46.2%. In this case, the interfacial stresses could be reduced and the end debonding can be avoided due to the increasingly tight anchoring effect, and the ultimate load can be increased even after partial debonding since the stress can continue to be transferred via mechanical anchorage. When the specimens were strengthened with HA CFRP, the surface treatment had a marginal influence on the strengthening effect. The strength of the slabs strengthened with HA CFRP decreased with the length of CFRP sheets, which is contrary to the trend of cases using EB CFRP. Finally, expressions were proposed to estimate the strain of the CFRP and load-carrying capacity of the strengthened members at the ultimate state, and the test results were within the range of the calculated results.