Structural Strengthening with Prestressed CFRP Strips with Gradient Anchorage
Publication: Journal of Composites for Construction
Volume 17, Issue 5
Abstract
This paper presents the principle and the application of an innovative anchorage technique for prestressed carbon fiber–reinforced polymer (CFRP) strips in structural strengthening. Additionally, large-scale static loading tests of retrofitted concrete beams are shown. The gradient anchorage, based on the adhesive’s ability to undergo accelerated curing at high temperatures, consists of a purely concrete-adhesive strip connection without any mechanical devices, such as bolts or plates. In a first step, this study summarizes anchorage techniques presented in the literature and introduces the basic principles of the new method as well as the necessary components. In a second step, an application on a full-scale RC beam is explained in detail. A commercially-available CFRP strip is prestressed up to 0.6% prestrain and subsequently anchored by sequential epoxy-curing and force-releasing steps at both strip ends. Furthermore, uniaxial tensile tests on the epoxy adhesive and the CFRP strip are used for material characterization and to demonstrate the reinforcing materials’ integrity after the heating process. It appeared that prestress losses during the anchoring phase are negligible. The method allows much faster installation than conventional mechanical techniques and increases durability because no permanent steel elements are necessary. The material tests indicate no damage in the reinforcing CFRP strip as well as a sufficiently fast strength development of the adhesive after accelerated curing. Static loading tests on strengthened large-scale RC beams are presented and show the efficiency of a prestressed CFRP strip with gradient anchorage as a retrofitting technique. Finally, first long-term measurements over 13 years on a prestressed strip bonded to a concrete plate revealed small prestrain losses.
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Acknowledgments
The authors want to thank the Swiss innovation promotion agency (CTI project No. 10493.2 PFIW-IW) as well as the industrial partner S&P Clever Reinforcement from Switzerland for their financial support. Furthermore, the staff of the Structural Engineering Testing Laboratory at Empa as well as from University of Minho is kindly thanked for their contributions to the experimental investigations. Particular acknowledgements are expressed to Milos Dimic for the CAD Inventor drawings as well as Professor Fernando Castro from the Department of Mechanical Engineering of the University of Minho for the SEM images. The second author would like to thank the Fundaão para a Ciência e a Tecnologia (Foundation for the Science and Technology/Portugal), grant SFRH/BSAB/1220/2011 for providing financial support in the context of his sabbatical year.
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Information & Authors
Information
Published In
Journal of Composites for Construction
Volume 17 • Issue 5 • October 2013
Pages: 651 - 661
Copyright
© 2013 American Society of Civil Engineers.
History
Received: Oct 3, 2012
Accepted: Feb 26, 2013
Published online: Feb 28, 2013
Discussion open until: Jul 28, 2013
Published in print: Oct 1, 2013
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