Basic HTML Version
347
IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 3
M. R. GARCEZ | G. L. C. P. SILVA FILHO | URS MEIER
Concrete structures post-strengthenedwith prestressed FRP also show
premature failures as described by Teng et al. [15]. However, in pre-
stressed systems, the high strength of the FRP used to post-strengthen
structures is much better used, and, depending on the configuration
of the post.-strengthening, tensile failure of the FRP may be achieved.
Garden and Hollaway [1] presented, in 1998, a specific study
regarding the failure modes of reinforced concrete beams post-
strengthened with prestressed FRP, with prestressing levels
ranging from 25% to 50% of the FRP strength. Results showed
that a high prestress level was required to enable the ultimate
capacity of strip to be reached, before shear displacement
reached its critical value.
According to Garden and Mays [4], the level of prestress that
can be applied will be limited by the tensile strength of the
FRP. Tensile failure of the FRP should not precede either
yielding of steel reinforcement or crushing of concrete, to en-
sure adequate ductility. Results of the experimental program
showed that the level of prestress may also have to be limited
by the strength of the anchorage devices, by the horizontal
shear strength of the adhesive/FRP interface and by the bot-
tom layers of concrete.
3. Experimental program
3.1 Description of specimens
Table [1] describes the first stage of the experimental program,
which aims to investigate the behavior of reinforced concrete
beams post-strengthened with prestressed CFRP strips under
static loading.
3.2 Reinforced concrete beams
The reinforced concrete beams were rectangular, 6500mm long,
1000mm wide, and 220mm deep. All beams were reinforced
with seven bottom 15mm steel bars (r = 0,0041). The shear re-
inforcement consisted of 8mm steel stirrups spaced each 90mm
(11,17cm²/m). Geometry and reinforcement details for the beam
are shown in Figure [6].
Figure 5 – Rupture of FRP close
to a flexural crack tip
FISSURA
Table 1 – Description of Experimental Program
Beam
Post-strengthening
Prestressing level
VT
-
Two CFRP
non-prestressed
strips
Two CFRP
prestressed
strips
-
-
35% of
e
fu
VFC_NP_01
VFC_PE_01
Figure 6 – Geometry and reinforcement details of tested beams