Page 46 - Riem-Vol6_nº2

217 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
C. M. PALIGA | M. V. REAL | A. CAMPOS FILHO
4.3 Discussion of the obtained results
Figure 13 presents the behavior of the three beams numerically
analyzed in series S2 in terms of maximum deflection, as a function
of applied load increase.
The efficacy of the strengthened system relative to ultimate loads
increased as the number of PBO-FRCM layers increased. In addi-
tion, the beams presented adequate ductility levels. The concrete
crushing that caused the beam with one PBO-FRCM layer to fail
happened after the tensioned reinforcement yielded.
When the behavior of the strengthened beams was analyzed, it was
observed that the strongest influence of the PBO-FRCM ratio also
happens after the tensioned internal reinforcement yielded, when the
strengthening system resistance capacity was effectively mobilized.
It must be noted that the beam strengthened with two PBO-FRCM
layers was approximately 32% more resistant than the one with
only one PBO-FRCM layer, whereas the beam with three PBO-
FRCM layers was approximately 6% more resistant than that with
two layers. Therefore, the 50% increase in strengthening system
area (from 13.5mm2 to 20.25mm2) contributed very little to increase
beam resistance. This is easily explained by the fact that these
beams failed due strengthening system debonding, suggesting
that increasing the number of PBO-FRCM layers may lead to pre-
mature beam failure due to strengthening system debonding and
therefore, the resistance capacity of this material is underutilized.
Figure 14 shows the bond stresses variations along the interface
concrete/strengthening system obtained numerically for the last
step before rupture load of beam series S1 e S2. The level of con-
crete/strengthening system bond stress for the beams strength-
ened with one PBO-FRCM layer (S1 and S2 – one layer) was low
before the beams failed, indicating the failure mode was not fragile,
that is, it was not caused by debonding of the strengthening from
the concrete substrate. On the other hand, beams strengthened
with two and three PBO-FRCM layers presented high bond stress
before the beams collapsed. These stress peaks, located between
58cm and 90cm from the support, were very close to the strength
of the bond between the concrete and the strengthening material,
indicating that failure was caused by debonding of the PBO-FRCM
system. Therefore, the failure modes determined numerically are
consistent with those obtained in the experimental tests.
5. Conclusions
The structural performance of the reinforced concrete beams ex-
ternally strengthened by a high-performance system consisting of
high-strength fibers in a cementitious mortar (PBO-FRCM) was
Figure 12 – Load versus Strain in the mid-span
section for Beam Serie S – Three layers2
Figure 13 – Load-deflection curves
(node 73 – Figure 4) for Beam Serie S2
Figure 14 – Bond stresses
concrete/strengthening system