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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
Post-strengthening of reinforced concrete beams with prestressed CFRP strips
Part 2: Analysis under cyclic loading
along the bottom of the beam. Measurements were made during
pre-loading, after 30.000 cycles, and after 100.000 cycles, with the
beam subjected to the maximum load (108kN).
Figures [06] and [07] also shows that the measurements made in the
CFRP strips allowed the construction of a well defined curve. Howev-
er, due to the crack growing between the gauge points, this behavior
could not be observed in the measurements made in the concrete.
Nevertheless all obtained responses followed an expected pattern.
Strains in the CFRP strips, at mid-span, during pre-loading, varied
from 2,00º/
oo
up to 2,50º/
oo
. At the end of 30.000 cycles, strains
increased to levels that varied from 2,50º/
oo
up to 3,00º/
oo
. From
30.000 cycles up to 100.000 cycles, it was not observed any sig-
nificant variation in the strains.
Strains measured, added to the strain applied to prestress each strip
(5,95º/
oo
), give for each strip a total strain of of 8,45º/
oo
and 8,95º/
oo
.
It is also noted that, at mid-span, where most of the cracks could
be found, strains measured in the concrete and in the FRP are
quite different. It happens because the FRP strip acts as a belt,
blocking the concrete crack opening. Therefore, it can be observed
that several points along to the beam are subjected to different
strains. Such points can, eventually, be related to the occurrence
of premature failures.
Strains at a distance of 1.2 m from both beam ends, out of the
loading region, are not greater than 1,50°/
oo
, however, these values
increased about 100% from preloading up to 100.000 cycles.
Figure [08] shows the strains in the CFRP strips measured dur-
ing pre-loading, after 30.000 cycles and after 100.000 cycles. Sig-
nificant variations were not observed in the range from 30.000 to
100.000 cycles. However, strains increased about 0,50º/
oo
from the
pre-loading up to 10.000 cycles.
Figure 7 – CFRP and concrete strains of beam VFC_PC_01, submitted to 108kN
after (a) 30.000 cycles and (b) 100.000 cycles
A
B
Figure 8 – CFRP strains of strip 01 (a) and 02 (b) of beam VFC_PC_01 during cyclic loading
A
B