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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 4
M. R. GARCEZ | L. C. P. SILVA FILHO | URS MEIER
cycles. Measurements after 1.000.000 and 5.000.000 cycles regis-
tered a maximum strain of 2,11º/
oo
. Such strain, added to the strain
applied to prestress each strip (5,95º/
oo
), give for each strip a total
strain of of 8,06º/
oo.
Strains in the strips of beam VFC_PC_02 were smaller to the
ones of beam VFC_PC_02, since, for the second beam, the
maximum load and the difference between the maximum and
the minimum load were smaller. Results of beam VFC_PC_02
indicate that, up to 5.000.00 cycles, it was not observed any
damage on the post-strengthening system, due to the applica-
tion of the cyclic loading.
Figure [16 (a)] shows the strains in the CFRP strips, measured
from the pre-loading up to 5.000.000 cycles. The most signifi-
cant variations occurred up to 1.000.000 cycles. Strains in the
CFRP strips varied about 0,85º/
oo
from the pre-loading up to
5.000.000 cycles.
The greatest differences regarding strains were found at 1,8m,
2,8m and 4,6m from the left side of the beam (Figure [16 (a)]), and
at 2,6m from the left side of the beam (Figure [16 (b)]).
Results indicate the existence of a kind of progressive strain at
the anchorage regions, which can, eventually, generate adherence
problems regarding long-term fatigue. Such effect should be better
investigated, however, the long time demanded to realize fatigue
tests, sometimes, inhibits this initiative.
Crack growing at mid-span of beam VFC_PC_01 can be observed
at Figure [17], which shows the results of all crack opening mea-
surements made, from pre-loading up to 5.000.000 cycles. Figure
[17] shows the results of crack openings and the respective posi-
tion from the left side of the beam, at mid-span, between the two
central loading points (signaled on the figure by two vertical arrows.
First cracks at mid-span appeared during pre-loading, reaching
less than 0,15mm. From this point up to 100.000 cycle, crack open-
ings increased, but did not exceed 0,20mm. After 1.000.000 cycles
the maximum crack opening was 0,22mm, and, after 5.000.000,
this value was not exceeded.
Cracking at the gradual anchorage regions appeared just after
100.000 cycles, however, the maximum cracking opening ob-
served was 0,05mm. From 100.000 up to 5.000.000 cycles, the
maximum crack opening measured at these regions was 0,10mm..
Results of crack openings obtained from beams VFC_PC_01 and
VFC_PC_02 cannot be compared directly, due to the difference
regarding the maximum and minimum loads applied to generate
the cyclic loading.
As the maximum load applied on the beam VFC_PC_01 (108kN)
was higher than the one applied on the beam VFC_PC_02 (78kN),
beam VFC_PC_01 showed higher values of crack openings since
pre-loading. Values of crack openings obtained after 5.000.000 cy-
cles, for beam VFC_PC_02, were reached by beam VFC_PC_01
after just 282.000 cycles.
5. Conclusions
Results of the reinforced concrete beams tested under cyclic load-
ing show that when these structures are post-strengthened with
Figure 13 – CFRP and concrete strains of beam
VFC_PC_02, submitted to 78kN, during pre-loading
Figure 14 – CFRP and concrete strains of beam VFC_PC_02, submitted
to 78kN after (a) 30.000 cycles and (b) 100.000 cycles
A
B