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Polymers 2014, 6(1), 114-131; doi:10.3390/polym6010114
Article

Prestressed CFRP Strips with Gradient Anchorage for Structural Concrete Retrofitting: Experiments and Numerical Modeling

1,* , 2
,
1
 and
1
1 Structural Engineering Research Laboratory, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstrasse 129, Dübendorf 8600, Switzerland 2 Department of Civil Engineering, University of Salerno, via Giovanni Paolo II 132, Fisciano 84084, Italy
Michels, J.; Czaderski, C.; Martinelli, E.; Motavalli, M. RC Beams Strengthened with Prestressed CFRP Strips with Gradient Anchorage; In 2nd conference on Smart Monitoring, Assessment and Retrofitting of Civil Structures (SMAR), Istanbul, Turkey, 2013.
* Author to whom correspondence should be addressed.
Received: 29 November 2013 / Revised: 23 December 2013 / Accepted: 24 December 2013 / Published: 6 January 2014
(This article belongs to the Special Issue Selected Papers from "SMAR 2013")
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Abstract

This paper presents a study on the load carrying capacity of reinforced concrete (RC) beams strengthened with externally bonded (EB) carbon fiber reinforced polymer (CFRP) strips prestressed up to 0.6% in strain. At the strip ends, the innovative gradient anchorage is used instead of conventional mechanical fasteners. This method, based on the epoxy resin’s ability to rapidly cure under high temperatures, foresees a sector-wise heating followed by a gradual decrease of the initial prestress force towards the strip ends. The experimental investigation shows a promising structural behavior, resulting in high strip tensile strains, eventually almost reaching tensile failure of the composite strip. Additionally, ductility when considering deflection at steel yielding and at ultimate load is satisfying, too. From a practical point of view, it is demonstrated that premature strip grinding in the anchorage zone is not beneficial. In addition, a non-commercial 1D finite element code has been enlarged to an EB reinforcement with prestressed composite strips. A bilinear bond stress-slip relation obtained in earlier investigations is introduced as an additional failure criterion to the code. The numerical code is able to almost perfectly predict the overall structural behavior. Furthermore, the calculations are used for comparison purposes between an initially unstressed and a prestressed externally bonded composite reinforcement. The increase in cracking and yielding load, as well as differences in structural stiffness are apparent.
Keywords: CFRP; structural retrofitting; externally bonded reinforcement; prestressing; gradient anchorage; experimental investigation; finite element model CFRP; structural retrofitting; externally bonded reinforcement; prestressing; gradient anchorage; experimental investigation; finite element model
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Michels, J.; Martinelli, E.; Czaderski, C.; Motavalli, M. Prestressed CFRP Strips with Gradient Anchorage for Structural Concrete Retrofitting: Experiments and Numerical Modeling. Polymers 2014, 6, 114-131.

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