Page 97 - Riem-Vol6_nº3

442 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
Numerical analysis of two pile caps with sockets embedded, subject the eccentric compression load
definition of the rupture superficies it is necessary only two pa-
rameters: the strengths to the last compression and traction of the
concrete. Concrete rupture criterion is analogue to William-Warnke
rupture criterion. Figure [10] presents the rupture superficies.
In all pile caps was adopted compressive strength of concrete (fck)
equal to 25 MPa.
For the steel bars, it was adopted perfect elastic-plastic behavior.
The elasticity module used was equal to 210 GPa, Poisson coef-
ficient equal to 0.3 and the tension steel equal to 500 MPa.
Through the tests performed, we verified that Newton-Raphson
criterion was the one which presented the best results regarding
the convergence of the models, thus, in all analyses this criterion
was used.
For the properties of the contact elements, it was used the Cou-
lomb friction model, being necessary to define the value of the
friction coefficient, m, the maximal shear stress, tmaximum and two
constants, FKN and FTOLN, FKN represent a normal rigidity coef-
ficient of the contact element and FTOLN constant is a tolerance
factor to be applied in the sense of the normal vector of the superfi-
cies. This factor is used to determine the penetration compatibility.
The contact compatibility is satisfied if the penetration is in permis-
sible tolerance (FTOLN measures the deepness of the underlying
elements). The deepness is definite by the average deepness of
each individual element of the contact in the pair. If the computer
program Ansys®[23] detects any penetration bigger than this toler-
ance, the global solution does not converge, even if the residual
forces and the displacement increments are found in the criteria
of the adopted convergence. For FKN coefficient we used value
equal to 1 and for FTOL value equal to 0.1.
The choice of the “correct” value of the friction coefficient is a hard
task, as it depends on several factors: type of superficies, intensity
of actions, mechanic properties of the materials which compose
the link column-foundation. There are, in the technical literatures
several indications for the value of the friction coefficient concrete-
concrete. According to Nielsen [10] the value to be used is 0.6,
EN 1992-1-1 [03] indicates that the friction coefficient value for
the situation where the link column-foundation by half precast with
smooth walls, must be higher than 0,3. Canha [11] and Ebeling [12]
analyzed the influence of the friction coefficient in links column-
foundation by half precast, varying the value of 0.60, 0.45 and
0.30. Osani et al. [13] suggests that the values of friction coefficient
have values equal to 0,5 and 1, function of the embed length and of
the king of the precast and column walls conformation. In this work,
suggesting the recommendations of Canha & El Debs [14] used
the friction coefficient equal to 0,6. It is important to remember that
this numerical analysis aims at presenting the behavior trend of the
link column-foundation behavior through embed precast in blocks
on two piles, with main end of analyzing the relevance of the ana-
lyzed factors.
Figure 9 – Finite Element Contact, Ansys®
Figure 10 – Failure Surface in Principal Stress Space,
Concrete, Ansys®