Calculation Technique for Externally Unbonded CFRP Strips in Structural Concrete Retrofitting
Publication: Journal of Engineering Mechanics
Volume 142, Issue 6
Abstract
This paper presents a calculation procedure for externally unbonded carbon fiber–reinforced polymer (CFRP) strips anchored at their ends in flexural strengthening of existing reinforced concrete structures. Due to strain incompatibility between the composite strip and the neighboring concrete surface, the well-known conventional cross-section analysis (CSA) employed for bonded reinforcements cannot be implemented. An iterative force equilibrium and strip strain adaptation with previously defined constitutive materials laws together with an optimization procedure in a numerical computing environment are used to overcome the computational complexities. For validation purposes, two static loading tests on reinforced concrete beams with an externally prestressed CFRP strip without bond except in the anchorage zones are compared to the numerical predictions. Prior to the final evaluation, a model for the anchorage resistance is implemented in the algorithm in order to capture the ultimate load due to anchorage failure. An excellent agreement in terms of structural behavior as well as of ultimate load-carrying capacity is observed. Eventually, the differences in the structural response between bonded and unbonded strips are pointed out.
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Acknowledgments
The authors want to acknowledge the support of the Swiss Federal Laboratories for Materials Science and Technology (Empa) staff for their assistance in the experimental testing. The financial support (No. 200021_124401/1) of the Swiss National Science Fundation (SNSF) for the doctoral studies of the third author is highly appreciated.
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Published In
Journal of Engineering Mechanics
Volume 142 • Issue 6 • June 2016
Copyright
© 2016 American Society of Civil Engineers.
History
Received: Jun 1, 2015
Accepted: Aug 12, 2015
Published online: Feb 23, 2016
Published in print: Jun 1, 2016
Discussion open until: Jul 23, 2016
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