Page 146 - Riem-Vol6_nº2

317 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 2
D. L. ARAÚJO | A. R. DANIN | M. B. MELO | P. F. RODRIGUES
Next to propitiating an increase in splitting strength of the concrete
cover, the incorporation of fibers also influenced the failure type,
which was less brittle than in concrete without fibers (Figure 8).
Furthermore, the addition of 2% fibers allowed the bar to reach the
steel’s yield stress before the splitting failure of the concrete cover,
as was registered by the strain gage glued to the external part of
the bar (Figure 9). This shows the positive effect of the steel fibers
in the concrete’s confinement in the anchorage bars region.
3.4 Computer modeling
The computer modeling of the pull-out tests was executed with
the DIANA® 9.3 software, based on the finite element method
[39]. In order to represent the concrete and the steel bar, iso-
parametric solid finite elements of type CHX60 were used, and
to represent the interface between the steel bar and the con-
crete, the interface finite element of type CQ48I was used, both
available in the software’s library. It should be emphasized that
in this modeling the possibility of slip between bar and concrete
was not considered, i.e. the perfect adhesion between both ma-
terials was assumed.
In a preliminary stage, the models were processed without the
representation of the ribs on the bars. In this study, it was veri-
fied that the physical representation of the bar’s ribs exerted
any influence on the results [37]. This way, all the computer
models presented here consider the presence of the ribs on
the bars.
Figure 10 shows the finite elements mesh that was used in the
modeling of the pull-out test for the bar of 10 mm diameter. The
choice for only modeling this bar diameter came from the fact that
it was wanted to numerically evaluate the bonding stress distribu-
tion between the bar and the concrete when the bar is pulled out
from the concrete without splitting. The size of the finite elements
mesh was defined in function of the ribs’ dimensions and in func-
tion of the minimum volume for the tridimensional finite element
allowed in the DIANA® 9.3 software. In this same figure is also
shown the boundary conditions scheme of the computer model,
which was restricted along the full length of its base.
Figure 8 – Failure by splitting of the concrete cover
Bar of 16 mm diameter and concrete without fibers
Bar of 20 mm diameter and concrete without fibers
Bar of 20 mm diameter and concrete with 2% fibers
A
B
C
Figure 9 – Load versus bar strain for test
specimens with bar of 20 mm diameter