Page 96 - Riem-Vol6_nº3

441 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
R.. G. DELALIBERA | J. S. GIONGO
of the comparisons among experimental and numerical results
were satisfactory, as presented in the item 3.3.
To represent the friction between the walls of the precast and the
filling material (grout) and the faces of the precast column, elements
of contact were used, being definite contact superficies between the
materials (contact superficies and target superficies). The contact
superficies between the materials were represented by tow finite
elements, named “contact pair”. For the contact superficies, the fi-
nite element Contact 173 was used and for the target superficies,
the finite element Target 170 was used. These elements have three
freedom degrees in each node and the geometric properties are the
same as in the faces of the solid elements to which they are linked,
which may have triangular or quadrangular geometry. Figure [9]
presents the contact pairs (element Contact 173 and Target 170).
The finite elements of contact were used only in the models with
smooth conformation of the walls of the precast and the column,
because, due to researches already performed by several re-
searchers, it can be considered that the link column-foundation
through precast with shear key have monolithic behavior.
3.2 Materials properties
Developing a model able to represent the concrete behavior as
close as the real behavior is a challenge. The reinforced concrete
is an almost fragile material and has different behaviors in the com-
pression and in the traction.
In the compression, the curve tension vs. deformation of the con-
crete is elastic and linear until nearly 30% of the last compres-
sion force. After this point, the concrete loses rigidity and follows
elevating the tension values until rupture force. Thereafter, there is
no increase of the tension suffering softening. In the traction, the
curve tension vs. deformation of the concrete is nearly elastic and
linear until the tension of the maximal traction. After this point, the
concrete cracks and its strength is not considering the softening in
the traction.
To model the concrete material, it is necessary to provide the pro-
gram Ansys®[23] the following input data: longitudinal elasticity
module of the concrete; ultimate strength of the concrete to com-
pression and traction; Poisson coefficient; and transfer coefficient
of shear. Ansys®[23] also allows as input data, the inclusion of a
tension stress vs. deformation to represent the mechanical prop-
erties of concrete. This is normally done, when by convergence
problems, the processing is abruptly interrupted by early crushing
of the concrete. Kachlakev et al. [9] bring bigger information on this
phenomenon. In the analyzed models, this problem did not occur.
The longitudinal elasticity module of the concrete, Ec, as well as,
the concrete traction strength, ftk, were determined based in the
recommendations of NBR 6118:2007 [1]. Poisson coefficient, n,
adopted to the concrete was equal to 0.2 and the shear transfer-
ence coefficients, b adopted were equal to 1 to open and closed
cracking. This value for the coefficient b was used, because tests
performed showed bigger efficiency in the convergence of the pro-
cessing when used the mentioned value, see Delalibera [5].
Concrete rupture criterion provided by Ansys® was used. For the
Figure 6 – Boundary conditions and finite element
Figure 7 – Solid 65, Ansys®
Figure 8 – Link 8, Ansys®