Flexural Strength and Ductility of FRP-Plated RC Beams: Fundamental Mechanics Incorporating Local and Global IC Debonding
Publication: Journal of Composites for Construction
Volume 20, Issue 2
Abstract
Reinforced concrete (RC) beams and slabs are frequently strengthened or stiffened in flexure by adhesively bonding fiber-reinforced polymer (FRP) plates to their surfaces using a strain-based moment-curvature design technique. This design technique is generally based on the intermediate crack (IC) debonding strain of the FRP reinforcement, that is, on the start of IC debonding; from this analysis it is often deduced that FRP plating is ineffective at the ultimate limit state because FRP debonding occurs before yield of the steel reinforcement. In this paper, it is shown that the strain-based approach is generally a lower bound at the ultimate limit state. Instead, a displacement-based approach is described that shows that FRP plated beams can be designed to achieve a higher strength than that of the RC beam by itself no matter when IC debonding first occurs. The mechanics of the analysis approach developed here treat the FRP debonded plate as a FRP prestressing tendon with a force equal to the IC debonding force. Consequently all FRP plated beams have the potential to achieve strengths greater than that of the unplated beam specifically when designed for ductility, which makes the system much more effective at the ultimate limit state. This paper describes, in a form suitable for the development of numerical solutions, the fundamental mechanics that control local IC debonding at a section or segment as well as global IC debonding along a member. It is shown how FRP plates and their extent of plating can be chosen through mechanics to increase the strength and if necessary the ductility of a member as well as allowing for both stable and unstable debonding.
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Acknowledgments
The authors would like to acknowledge the support of the Australian Research Council ARC Discovery Project DP140102695 “Quantifying the durability of FRP retrofitted clay brick masonry buildings” and the Commonwealth of Australia through the Cooperative Research Centre program.
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Published In
Journal of Composites for Construction
Volume 20 • Issue 2 • April 2016
Copyright
© 2015 American Society of Civil Engineers.
History
Received: Mar 17, 2015
Accepted: Jun 29, 2015
Published online: Aug 14, 2015
Discussion open until: Jan 14, 2016
Published in print: Apr 1, 2016
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