Basic HTML Version
165
IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 1
T. E.T. BUTTIGNOL | L.C. ALMEIDA
4. Conclusion
The increase in the concrete compressive strength was not fol-
lowed by a significant augment in the pile cap’s load bearing ca-
pacity and structural behavior. In addition, pile cap’s stiffness was
not altered.
In all three models, a brittle collapse was observed due to
concrete crushing in the inferior nodal zones, concrete split-
ting, and the yielding of the ties. Despite the small incre-
ment in the ultimate load caused by the concrete compres-
sive strength increase, the influence of high tensile stresses
through the struts and the nodal zones was determinant to
the pile cap’s collapse.
In all models analyzed, there was no perceptible variation in the
crack pattern. Nevertheless, in percentage, there was a higher re-
duction in the pile caps opening cracks in relation to the increase
of the concrete’s tensile strength.
In all three models a concentration of compressive stresses in the
piles cross-section closest to the column was observed.
Concrete compressive strength increase led to a proportional in-
crease of the struts compressive stresses.
In all models, the ties reinforcement yielded and there was a signif-
icant decrease of the ties stresses in the inferior nodal zones due
to the positive action of compressive struts stresses. At the ends
of the bars and on the hooks stresses were practically null, thus
corroborating that hooks anchorage in pile caps is unnecessary.
5. Acknowledgments
To FEC-UNICAMP for the provision of all necessary tools for the
development of this research which has resulted in a participa-
tion and presentation of a paper related to this subject in the 53º
Brazilian Concrete Congress with a subsequent publication in the
Congress Annals.
Figure 8 – Principal compressive stress flow (ATENA)
Table 9 – Struts compressive stress variation (
) in relation to the f
c
ck
Struts compressive
stress variation
Pile cap
f
ck
f
ck
Struts stress
(
)
c
c
Model 1
30 MPa
-
21 MPa
-
Model 2
35 MPa
16,66%
25 Mpa
19,05%
Model 3
40 MPa
14,28%
29 MPa
16,00%
Table 10 – Compressive stresses in the
nodal zones at the ultimate load
Compressive
strength
(MPa)
Pile cap
Inferior
nodal
zones
Superior
nodal
zones
Model 1
> 30
24
Model 2
> 35
28
Model 3
> 40
30
Table 11 – Pile caps tensile stresses
at the ultimate load
Tensile stresses
(MPa)
Model 1
> 2,58
Model 2
> 2,86
Model 3
> 3,13