Page 42 - Riem-Vol6_nº2

213 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
C. M. PALIGA | M. V. REAL | A. CAMPOS FILHO
ment, which were determined in standardized specimen tests (at
least three per diameter).
3. Finite element numerical model
3.1 Model for concrete
Concrete is represented by two-dimensional isoparametric eight-
node finite elements for plane stress state. The constitutive two-di-
mensional model for concrete is based on the model proposed by
Darwin and Pecknold [6] employing the equivalent uniaxial strain
and the two-dimensional failure criterion of Kupfer and Gerstle [7].
For the tensioned concrete after cracking, a curve that includes
softening was adopted to take into account concrete contribution
to tension-stiffening between cracks.
3.2 Model for steel
Reinforcement is represented by the embedded model, based on the
study of Elwi and Hrudey [8]. Each reinforcement bar was considered
or three 15cm-wide PBO-FRCM layers. The mechanical properties
of the PBO fabric are presented in Table 1.
Table 2 shows tensile reinforcement ratio, compression ratio, and
PBO fibers reinforcement ratio of each series.
During the process of beam manufacturing, curing was performed at
environmental temperature, and the prototypes were strengthened
30 days after concrete placement. In order to ensure good bonding
conditions between concrete and the mortar substrate, the beams
were sandblasted to remove cement powder, washed with water,
and left to dry at environmental temperature for a few days. After
the first mortar layer was applied on the concrete substrate, the first
layer of PBO fabric was applied and slightly pressed inside the mor-
tar. A second mortar layer was then applied to completely cover the
PBO fabric, and this operation was repeated until all PBO fabric lay-
ers were applied and covered with mortar (Ombres [1]).
Concrete mechanical properties were determined after at least 28
days of concrete placement using cubic or cylindrical test speci-
mens. Mean compressive strength, fcm, tensile strength, f tm, and
elastic modulus, Ecm, values are presented in Table 3. The same
table shows mean yield strength values of the internal reinforce-
Table 1 – Mechanical properties of PBO fabric mesh and cementitious mortar
Nominal thickness Elastic modulus Tensile strength Tensile strain Compression strength
(mm) (GPa) (MPa) (‰) (MPa)
PBO fiber
mesh
0.0455 (longitudinal)
0.0224 (transversal) 270 5,800 21.5 -
Mortar - 6 3.5 - 29
Table 2 – Amount of internal reinforcement and strengthening in each series
Beam serie Number of strengthening layers As A’s Af s f
2 (mm ) 2 (mm ) 2 (mm ) (%) (%)
S1
1 339.30 157.00 6.75 0.905 0.018
1 339.30 157.00 6.75 0.905 0.018
S2
1 157.00 100.53 6.75 0.419 0.018
2 157.00 100.53 13.50 0.419 0.036
3 157.00 100.53 20.25 0.419 0.054
Table 3 – Materials properties
Beam serie fcm ftm Ecm Internal reinforcement diameter fym
(MPa) (MPa) (MPa) (mm) (MPa)
S1 22.77 (c.o.v=4.38%) 2.03 28,140 12 515.44
10 521.89
S2 23.02 (c.o.v=6.70%) 2.12 28,160 10 525.90
8 535.60