Normalized test for prediction of debonding failure in concrete elements strengthened with CFRP: Fid-Bau Portal

Normalized test for prediction of debonding failure in concrete elements strengthened with CFRP

Ramos, G. / Casas, J.R. / Alarcon, A.

This work presents the results of an experimental research program, earned out at the Technical University of Catalonia, to study the debonding behavior of carbon fiber-reinforced polymers (CFRPs) used to strengthen beams in bending. The research is a part of a program that aims to study the strengthening of concrete bridges (both monolithic and segmental) using CFRPs. The overall objective of this paper is to present the results obtained from bond tests performed on material-scale specimens and full-scale tests performed on monolithic and segmental beams. A normalized test is proposed to obtain a more reliable estimate of the debonding strain of CFRPs, which may govern the design of CFRP-strengthened concrete structures. The test is proposed to supplement available design models, as the formula of km included in ACI 440.2R-02 by ACI Committee 440. The results from the tests are checked with the data obtained in large-scale tests, representative of actual bridges. The reported values are significantly lower than those reported in other tests with specimens of a lower size. An explanation is that a size effect can exist, which affects the debonding failure mechanisms. Extrapolation of results - from models calibrated with specimens of reduced dimensions to real structures - may lead to unsafe predictions of the debonding strain. In conclusion, the proposed simplified bond test more accurately estimates the load bearing capacity, which in practical cases is not perfectly well covered by the existing models; for instance when discontinuities (cracks or joints) are present in the concrete where the CFRP is bonded.