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IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 1
RC T beams strengthened to shear with carbon fiber composites
1. Introduction
Concrete carbon fiber strengthening
has been widely used over
the last 20 years in several countries, and can be considered a
well-established construction procedure. But during the last few
years, important research has contributed to new design and anal-
ysis models for the strengthening system currently used by engi-
neers ([1], [2], [3])
The technique of strengthening reinforced concrete beams with
externally-bonded composite materials has been shown to be ef-
ficient. Results obtained from reports and manuals concerning the
state-of-the-art of this technique indicate that the shear strength-
ening of reinforced concrete has some confusing and unexplained
features. This is due to the fact that the composite material, glued
to the concrete surface, has linear-elastic behavior, quite different
to the non-linear behavior of the structural element.
The shear strengthening of reinforced concrete beams in bridges
and buildings may be applied due to several causes: design, faults,
increased load, functional changes, environmental attacks, etc. The
mechanisms by which shear is carried out in reinforced concrete
beams are very complex, and still not well understood. In general, the
contribution of the shear reinforcement is calculated according to the
truss analogy (steel and CFC). The shear resistance offered by con-
Figure 1 – Cracking sliding model
Idealized diagonal cracks
Stress distribution at formation of a crack
A
B