Enhancing the Debonding Strain Limit for CFRP-Strengthened RC Beams Using U-Clamps: Identification of Design Parameters

Abstract

In simply-supported reinforced-concrete (RC) beams strengthened by carbon-fiber-reinforced polymer (CFRP) plates, plate debonding is initiated at the beam ends, where the principal compression, predominantly composed of a vertical component, detaches the plate externally bonded to the unconfined cover concrete. A CFRP wrap acting as a U-clamp can provide confinement to enhance the moment capacity by resisting premature cover debonding. The wrap design parameters in terms of clamping location, width, and stiffness were identified from a set of fundamental experiments. The ultimate moment capacities of 22 tested specimens with different end anchorage conditions were compared against control specimens. The debonding strain, and consequently the ultimate moment capacity, gradually increased with increasing U-clamp width and stiffness. The failure patterns confirmed the effect of U-clamps in inducing a partial confinement effect on the sides and bottom of a beam end. The resulting changes in the compressive principal stress distribution in the compression arch were considered in formulating relationships for debonding strain prediction. The proposed relationship successfully predicted values regarding strengthened stone and brick aggregate concrete beams. The relationships for both unclamped and U-clamped anchorages better reproduced the experimental moment capacity enhancements than did the known equations. To assess the derived relations’ wider applicability, the estimates obtained using the proposed relations were compared against published results for 42 test beams.