Page 98 - Riem-Vol6_nº3

443 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
R.. G. DELALIBERA | J. S. GIONGO
In relation to the shear tension, tmaximum, we adopted the value used
by the computer program, [σy /(3½)], in which σy is the strength to
the outflow of the rupture criterion of Von Mises, of the underlying
material to the contact superficies. For σy we used values indicated
by Canha [11], where this tension values thirty per cent of the com-
pressive strength of concrete of minor strength belonging to the
contact. Therefore, σy value adopted was equal to 7.5 MPa, result-
ing 2.5 MPa for the value of tmaximum.
3.3 Comparative analysis
In order to verify if the adopted models for the numerical analy-
sis of the two pile caps show correct behavior trend, comparative
analysis of experimental tests and numerical simulations of several
researchers. In this work, it will be presented the results of the
comparative numerical analyses of the tests performed by Mautoni
[15] and Adebar et al. [16] and of the numerical simulation devel-
oped by Sam & Iyer [17]. In Delalibera [5], it can be observed the
rest of the comparative analyses performed and more details of the
numerical analyses developed.
In the comparative analysis, we also used the same finite elements
used in the analyses of the two pile caps, i.e., Solid 65 – discretiz-
ing the concrete material and Link 8 – modeling the steel bars.
All mechanic and geometric properties adopted in the comparative
analysis were the same as in the experimental tests. The contour
conditions used in the tests with higher possible reality degree, the
same thing happening to the loading.
The first comparative analysis is of the pile cap B1-A tested by Mau-
toni [15]. The pile cap had rupture by shear with last force equal to
800 kN. The first crack appeared with nearly thirty per cent of the last
force, about 240 kN. The pile caps was twenty five centimeters high,
the column was squared with a 225 cm² area and the piles had trans-
versal sections equal to 10 cm x 15 cm. The compressive strength of
concrete was equal to 32.30 MPa and the steel bars of the tie pre-
sented strength of equal to 720MPa. As there was no information on
the elasticity module and on steel and concrete Poisson coefficients,
we adopted the recommendations of NBR 6118:2007 [1].
We applied the numerical model three hundred force increments,
whereas to each increment the applied force value was 2,67 kN.
Figure [11] shows the final configuration obtained in the experiment
and in the simulation of the block B1-A.
The force value which originated the first crack in the numerical
model was 312,33 kN. It occurred difference of 23.15% in relation
to the force value which originated the first crack in the experi-
mental model. It occurred because in the experimental model, the
force that provoked the first crack was determined as a function of
visual observation, i.e, the first crack visible to the human eye. In
relation to the last force, the numerical model presented last force
of 799,98 kN, practically, did not occur difference with the value
experimentally obtained.
The second comparative analysis is two blocks tested by Adebar
et al. [16]. Pile caps A, B, C, D and F were simulated. All pile caps
were sixty centimeters tall and Poisson coefficients equal to 0,3
and 0,2 for steel and concrete respectively. In all pile five hundred
force increments were applied.
Pile cap A was constituted by four piles of twenty centimeters and
column with squared transversal section with thirty centimeters
side. The average compressive strength of concrete (fcm) obtained
in the tests was equal to 27,10 MPa. The steel bars had tensile
strength equal to 479 MPa. In the test, the first crack emerged with
force equal to 1186 kN and the rupture force was equal to 1781 kN.
In the numerical model, the first crack occurred with force equal
to 1403,86 and the ruin force obtained was equal to 1781,10 kN.
Pile cap B had the same geometric properties of Pile cap A, how-
ever, the reinforcement was distributed on piles, while in Pile A, the
reinforcement was distributed in mesh. The compressive strength
of concrete was 24,80 MPa and the tensile strength the steel bars
of the tie was the same as in Pile cap A. In the test, the first crack
emerged for a 1679 kN force, now, in the numerical model, the first
crack occurred with 1505,71 kN. The experimental ruin force was
registered with value equal to 2189 kN and in the numerical simu-
lation, the force obtained was 2186 kN.
Pile cap C had six piles with diameters of twenty centimeters and
column with the same transversal section of the other models. The
Figure 11 – Final configuration of the pile cap B1-A, tested by Mautoni (1972)