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218 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
Numerical analysis of reinforced concrete beams strengthened with high strength cement-based
composite material
numerically analyzed in this study. The obtained results allow the
following conclusions.
The finite element model used for numerical simulations has shown
to be a valuable tool to analyze this type of problem. Its efficiency
was demonstrated when the results were compared with the ex-
perimental values presented by Ombres [1]. Despite the different
failure modes, the numerical model achieved an average approxi-
mation of 2.8% for failure loads relative to the experimental values.
The use of the PBO-FRCM system significantly improved the flex-
ural strength of reinforced concrete beams. The results showed an
increase of approximately 39% in load capacity when the external
reinforcement material was applied (from 52.25kN to 72.75kN).
However, increasing PBO-FRCM ratios may lead to beam failure
due to debonding of the strengthening system. This represents
an underutilization of the strengthening material, as it cannot be
submitted to maximum strain. This is shown by the increase in ap-
proximately only 6% in the rupture load of the beams with three
strengthening layers (Af =20.25mm2 – P u=72.75kN) relative to
those relationship with two layers (Af=13.50mm2 – Pu=68.75kN).
According to Ombres [1], these beams failed due to the debonding
of the PBO-FRCM system from the concrete substrate.
Beam ductility was adequate. Even when beams failed due to
concrete crushing, this happened after the tensioned internal re-
inforcement yielded.
The strongest influence of the PBO-FRCM ratio on beam stiffness
happens after the tensioned internal reinforcement yielded. Before
cracking, there is no influence of the PBO-FRCM ratio on beam be-
havior, as it depends almost exclusively of the stiffness of the concrete
section that is still intact. After cracking load, the increase in stiffness
as the number of layers increase is minimal, as the dependence of the
tensioned internal reinforcement is higher. After the tensioned internal
reinforcement yields, beam resistance starts to depend almost exclu-
sively of the strengthening material. There is a significant increase in
stiffness as PBO-FRCM system area increases.
When premature failure modes are prevented, the simple models
commonly adopted to predict resistance are capable of providing
reasonably accurate approximations. However, when external
strengthening PBO-FRCM system debonding is expected, more
sophisticated models should be used to provide realistic predic-
tions of the resistance capacity of strengthened beams. Therefore,
numerical models based on the finite element method are very
useful to analyze this type of problem.
6. References
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beams strengthened with a cement based high
strength composite material. Composite Structures,
v.94, Dec, 2011; p.143-155.
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