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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 5
V. J. FERRARI | J. B. DE HANAI
In the initial stage is where begins the tension process of steel
fibers and microfibers and the stress transfer among the crack
surfaces through these fibers. In this stage, in which occurs the
formation of the cracks surfaces, it is observed that the crack de-
velops more than the material gain resistance to fracture. In the
last stage of the cracking process is when it is verified a consider-
able increase in fracture resistance for the composite due to the
pulling out of fibers, which are anchored to the cement matrix. At
this stage, the efficiency of fibers in relation to the contribution for
the increase of fracture toughness is notably reflected.
3. Retrofitting and strengthening
of tensile zone of RC beams
3.1 Characteristics of the beams
Three RC beams 3600 mm long were tested. All the specimens were
designed to have the same nominal cross sectional dimensions: 170
mm x 350 mm. The lower longitudinal reinforcement of beams con-
sisted of two steel bars CA50, with 12.5 mm diameter. The upper
reinforcement was composed of two steel bars CA50, with 6.3 mm
diameter. The transverse reinforcement was formed by stirrups with
steel bars CA50 of 6.3 mm diameter, evenly spaced at every 120 mm.
The characteristics of each beam are described in Table 3.
The beam V1A without strengthening was used as reference.
From this reference were established considerations related to in-
crement of resistance and stiffness provided by the strengthening.
The beam V1A was designed with a reduced rate of longitudinal
reinforcement so that its final limit state is characterized by the
excessive deformation of reinforcement without rupture in the com-
pressive concrete.
The beam V1C was flexural strengthened through the applica-
tion of three sheet layers of carbon fibers. The strengthening was
designed with the intent to detect its premature detachment. The
beam V2C was designed to compare directly its performance with
that of the strengthened RC beam. This comparison aims to detect
the contributions of the transition layer before detachment and on
the strengthening performance. For this purpose, the tensile zone
of beam V2C was demolished and subsequently reconstructed by
applying high performance cement-based composite CPM1A2C
(Figure [6]). The composite CPM1A2C was by presenting a satis-
factory performance in terms of flexural strength and fracture resis-
Ta��e � � Characteristics �� �eams
Beams
Characteristics
V1A
RC beam. Without strengthening. Control
V1C
RC beam model strengthened by three layers of CFRPsheets
V2C
The tensile zone was demolished and retrofitting with high performance cement-based.
RC beam model retrofitting and flexural strengthened by three layers of CFRP sheets
Figur�������������i������������������
P/2
P/2
A
A
200
200
strengthening with CFRP-sheets
three layers
transition layer
cement-based composite: CPM1A2C
3,200 mm
270
170
350
Section A-A
80