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1. Introduction
This paper shows the results of an experimental program de-
veloped at LEME-UFRGS, in Brazil, and at EMPA, in Switzer-
land, regarding the application of CFRP post-strengthening
on concrete structures. Continuing the results of the first part
of this paper, this second part analyses the behavior of con-
crete beams post-strengthened with prestressed CFRP under
cyclic loading.
2. Post-strengthened elements submitted
to cyclic loading
Fatigue may be defined as a permanent and progressive dam-
age process that induces gradual and cumulative crack growth
and might, ultimately, result in the complete fracture of the ele-
ments subjected to cyclic loads, if the stress variation and the
number of load cycles are large enough. This term was estab-
lished by the first researchers of the theme due to its nature:
a progressive damage process caused by cyclic loads, difficult
to observe, that changes the ultimate capacity of the material
[Menehhetti et al. [1]].
The usual fatigue failure mechanism for post-strengthened RC
beams, when subjected to cyclic loads, is marked by the rupture
of one of the steel rebars, followed by a stress redistribution that
overloads the remaining bars.
Meier U. [2] highlights that the steel rebars fail before the FRP
post-strengthening, as can be seen in Figure [01] that shows the
steel rebars of a post-strengthened concrete beam after a fa-
tigue failure. However, cyclic loads can also damage the adhe-
sive and affect the interface concrete-adhesive and adhesive-
FRP, leading to premature failures.
According to Ferrier et al. [3], the performance and the durabil-
ity of a concrete structure post-strengthened with FRP, when
subjected to cyclic loads, depends not only on the FRP fatigue
behavior but also depends on the interface concrete-adhesive
and adhesive-FRP.
Authors point out the importance of understanding the behav-
ior of these materials under cyclic loading, since a typical re-
inforced concrete highway bridge deck with a design life of 40
years may experience a minimum of 58x10
8
loading cycles of
varying intensities.
3. Experimental program
3.1 Description of specimens
Aiming to analyze the behavior of concrete beams post-strength-
ened with prestressed CFRP strips, under cyclic loading, three
421
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
M. R. GARCEZ | L. C. P. SILVA FILHO | URS MEIER
Figure 1 – Failure of concrete beam
after fatigue loading test
Table 1 – Description of Experimental Program
Beam
Post-strengthening
Test
Prestressing level
applied on the
strips
Stress range of
fatigue loading*
VFC_PE_01
Two CFRP
prestressed strips
Bending
static loading
35% of
e
fu
-
VFC_PC_01
Bending
ciclic loading
50% to 80%
VFC_PC_02
50% to 60%
* Related to the load that corresponds to yielding of the steel rebarat beam VFC_PE_01.