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IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 1
T. E.T. BUTTIGNOL | L.C. ALMEIDA
section and in the lateral faces within the struts, as illustrated by
Figure 6. In addition, a fragile collapse was observed due to con-
crete crushing in the inferior nodal zones, concrete splitting and
ties bars yielding.
The pile caps ultimate strength capacities were very close in all
three models, as shown in Table 6, demonstrating that the increase
in the concrete’s compressive strength and tensile strength did not
exert a significant influence in the pile cap’s load bearing capacity.
An increase of 33,33% in the concrete’s compressive strength
(from 30 MPa to 40 MPa) and of 21,20% in the concrete’s tensile
strength (from 2,58 MPa to 3,13 MPa) caused a meager increase
of 13,32% in the pile cap’s ultimate load, from 2.756 kN to 3.123
kN. Table 6 presents the correlations between the concrete com-
pressive strength and ultimate load variations.
Figure 7 shows the load
versus
displacement curve where it is pos-
sible to notice the great similarity in the behavior of the three pile
caps. It is important to stress that no variations in the pile caps
stiffness were observed.
3.2 Cracking pattern
In all three models the first superficial cracks appeared in the cen-
ter of the pile cap’s inferior section, expanding through the center
of the pile cap’s span and towards the pile cap’s superior faces. In
the ultimate load, intense cracks occurred in the pile cap’s inferior
section and in its lateral sections, as can be seen in Figure 6.
Table 5 – Contact elements properties
Contact element
Values
Normal stiffness parameter (K )
nn
5
3
2,0 . 10 kN/m
Tangential stiffness parameter (K )
tt
5
3
2,0 . 10 kN/m
Cohesion
0,0
Friction coefficient
0,0
Concrete ultimate tensile strength (f )
tk
3,2 MPa
Figure 6 – Crack pattern in the ultimate load (ATENA)
Table 6 – Ultimate load variation (
f ) in relation to the concrete compressive strength
ck
f
ck
f
ck
f
tk
f (%)
tk
F (Ultimate load)
u
F
u
Model 1
30 MPa
-
2,58
-
2.756 kN
-
Model 2
35 MPa
+16,66%
2,83
+9,69
2.940 kN
+6,68%
Model 3
40 MPa
+14,28%
3,13
+10,60
3.123 kN
+6,22%