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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 2
T.E.T. BUTTIGNOL |
L.C ALMEIDA
dance with Ramos [12] observations who demonstrated, through
computational analysis, that “pile caps structural behavior is highly
influenced by piles type of support and by pile cap stiffness”.
3.2 A resume of Delalibera [1] experimental results
Delalibera’s [1] results demonstrated that pile caps resist until the
beginning of concrete crushing, when a fracture plane along the
struts is started due to shear forces action. Ruin occurred by con-
crete crushing in nodal zones and by pile caps splitting along the
compressive struts. In most cases, concrete collapse occurred be-
fore reinforcement yielding.
The strains on the ties were not constant over the reinforcing bars.
A significant stress reduction has taken place in the inferior nodal
zones. And the strains at the ends of the steel bars of the ties were
close to zero, despite the existence of anchorage hooks.
In the model with splitting reinforcing bars (steel bars disposed
perpendicularly in relation of struts and with the purpose to absorb
tensile stresses and to resist to concrete splitting) proposed by [1],
an increase in pile caps resistance was observed. This model pre-
sented intensive strains in struts cross-section.
All experimental models presented a similar structural behavior,
with initial cracking beginning in the inferior nodal zone, at the pile-
pile cap interface, and propagating up to the superior nodal zone,
at the column-pile cap interface. Cracks were propagated over the
struts forming a clear rupture plane.
From principal compressive stress, [1] detected a greater concen-
tration of stresses at the column-pile cap contact surface and in the
piles region located at the beginning of inferior nodal zone.
4. Results and discussion
of the numerical models
4.1 Crack pattern
In all numerical models, first cracks appeared in the inferior nodal
zone at the piles-pile cap contact surface, and propagated along
the compressive struts up to the superior nodal zone. During load
increments a wide range of cracks parallel to the struts developed,
as shown in Figures 6 and 7.
In models 2 and 3, with piles supports reduction, an augment of
cracking intensity occurred during the loading. The formation of
cracks was observed cracks in the base of the piles and in its adja-
cencies due to geometric eccentricity. This eccentricity generated
a rotation in the axis of the piles and consequently a region with
stress concentration as it can be noted in Figures 7 (a) and 7 (b).
In model 4, splitting reinforcing bars effectively contributed to pile cap’s
cracking control. A reduction in crack opening intensity also occurred.
Figure 1 – Details of pile caps geometry and reinforcement bars (stirrups and ties)
Figure 2 – Details of model 4 splitting
reinforcement bars