Page 94 - Riem-Vol6_nº3

439 IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
R.. G. DELALIBERA | J. S. GIONGO
Figure [5] presents the finite elements net used to discretization of
the elements of the volume (concrete) and the bar elements (steel
bars of the reinforcement).
The normal force was considered through a pressure of 20 MPa
applied on the top of the column. The moment was considered
through a horizontal force, also applied on the column top, which
value was equal to 100 kN, generating a moment in the column
base of 100 kNm. See Figure [04].
As the models were symmetric, it was used the resource of sym-
metry. Therefore, it was analyzed only half of the structural ele-
ment. The translations were restricted (in the three directions, x, y
and z) of the element nodes placed on the tips of the piles. Figure
[6] presents the conditions of shape used in the models.
The length of a meter of the piles and the column, was chosen
in function of the principle of Saint – Venant, thus, the influences
were eliminated from the disturbances of stress in the areas of ap-
plication of the forces and in the areas of translation restrictions.
3.1 Finite element used
For the modeling of the concrete material, we used the finite ele-
ment Solid 65. This element has eight nodes with three degrees of
freedom per node – translations in the directions x, y and z. The ele-
ment presents plastic deformations, cracking and crushing in three
orthogonal directions. In the element Solid 65, the cracking occurs
when the main stress of the traction in any direction reaches the
rupture superficies. After the cracking, the elasticity module of the
concrete has value equal to zero in the considered direction. The
so, that the total heights of the models and the inclination angles of
the compression rod also suffered variations. For the pattern pile
cap we adopted piles of squared transversal section equal to 30
cm side, column also with squared transversal section, however
with 40 cm side. The embed length of the column in the pattern
pile cap was equal to 60 cm. This value represents the minimal
embed length for smooth walls (precast and column) specified in
NBR 9062:2006 [2], when the relation [Md/(Nd∙h)] ≤ 0,15. Figure [3]
presents the geometric properties of the pattern pile cap.
The distance between the axles of the piles was determined in
function of the inferior limit angle established by the French re-
searchers, in other words, 45°. Therefore, the total height of the
pattern block was equal to 90 cm, and the dimensions in plants
were equal to 240 cm for 84 cm. The distance between the axles of
the piles of all pile caps was equal to a hundred eight centimeters.
The embed length of the piles in the inferior face of the pile caps
followed the suggestion of the Montoya et al. [8], namely, it was
inlaid ten centimeters of the pile shaft inside the pile cap.
In relation to the columns and the piles the compression strength
concrete was equal to 50 MPa seeking to avoid, thus, ruining these
elements. The reinforcement of the piles were composed by eight
steel bars with a 20 mm diameter with strength equal to 500 MPa,
totalizing an steel area equal to 32.7 cm2. The external length of
the column was equal to 100 cm.
For the filling material, we adopted compression strength concrete
equal to 50 MPa (value equal compression strengths concrete of
the column).
Figure [4] shows the factors which present variations in the numeri-
cal analysis.
Table [1] presents the properties of the analyzed pile caps in re-
lation to the conformation of the smooth walls and to the shear
key (rough), requested by the compression force supposedly
centered in the column and by a horizontal force applied on the
top of the column.
The nomenclature used in Table [1] is described: L, pile with
smooth conformationof the walls of the precast and the column;
R, rough conforma- tion of the precast and the column; ℓe80,
embed of the column equal to eighty centimeters (more numbers
are analogue); hs30, thickness of the bottom slab equal to thirty
centimeters (more numbers are analogue); NM means that eccen-
tric compression force was applied.
In the same table, Ast represents the area of the transversal section
of the reinforcement class CA-50, Blx the length of the pile cap, Bly
the breadth of the pile cap, ℓemb the embed length of the precast
column and hs, the thickness of the pile cap bottom slab.
Using the indications of Blévot & Frémy [4], it was performed a
forecast of the resistant capacities of the pile caps.
3. Numerical analysis
The goal of the numerical analysis was to provide results for the
application of a statistical analysis named ANOVA (variance analy-
sis), thus, two piles caps with embed precast, with conformation of
the smooth and rough walls were analyzed. The numerical analy-
sis did not aim at calibrating bends of experimental results, but
presenting behavior trends of the analyzed models.
The geometry of all models were created in the computer program
AutoCad® and exported to the computer program ANSYS®[23],
through the extension SAT.
Figure 4 – Variation of factors chosen