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IBRACON Structures and Materials Journal • 2013 • vol. 6 • nº 3
Numerical approach of the bond stress behavior of steel bars embedded in self-compacting concrete
and in ordinary concrete using beam models
1. Introduction
Nowadays, the use of high-performance concrete is more and
more frequent, due to its economy and versatility. The need of high
reinforcement ratios to guarantee the material an appropriate duc-
tility causes many difficulties in the cast operations, requiring extra
care to assure the good quality of the structure.
Self-compacting concrete (SCC) is an innovative construction ma-
terial developed for civil constructions in the 1990’s that can be the
response for this problem. SCC is defined as a mixture that can be
cast in any place of the formwork, just through the accommodation
due to its own weight [1-2]. This new material is capable of flowing
inside the formwork through the reinforcement, filling it out without
any compacting equipment. As a result, increase of productivity,
reduction of labor costs and improvement of overall quality of the
structure can be obtained. [3].
The application of SCC is also expected to improve the flexural
behavior of the elements due to its superior filling capability, since
an increase of the bond resistance between reinforcement and
concrete could indirectly benefit the confinement effects. For low
strength concretes, SCC and OC (ordinary concrete) presented
similar bond strength, with some peculiarities [4-7]. Particularly in
places with high reinforcement rate the fresh properties of SCC
surpass the OC [8], producing higher quality elements. For high
strength concretes, similar results are expected, since the modu-
lus of elasticity will increase proportionally for both types of con-
crete, and those are the main properties of concrete affecting the
bond strength.
The bond between steel and concrete has been object of study
from the middle of the XX century, since the interaction between
steel and concrete is considered the main mechanism character-
izing the reinforced concrete behavior. As stated before, the ob-
tained bond strength depends on the steel bar and concrete prop-
erties, but steel the behavior is know well known. Therefore, the
study of bond goes through the complete knowledge of the materi-
als involved in the concrete production.
If from the physical point-of-view steel-concrete bond is still not
completely understood, the real behavior of the interface is very
difficult to be represented by numerical models, being affected
by a large number of variables. According to [9], the bond resis-
tance can be divided in three portions. The first one is the adhe-
sion, which consists of the shear resistance between concrete
and steel; the second is the friction between surfaces, which is a
decisive factor at the ultimate limit state; and the last one is the
bearing action, caused by the deformation of the bars in contact
with concrete.
There are several types of failure associated to the loss of bond
between concrete and the steel bar, and the main ones are pull-
out failure and splitting failure. These failures are strongly in-
fluenced by several factors, such as the type of reinforcement
(bar, tendons and strings), surface characteristics (flat or rough),
bar diameter, presence of confinement reinforcement, distance
among the bars, concrete cover, steel bar stresses, concrete
quality and others.
In the pull-out test of a steel bar from a concrete prism the failure
of the concrete occurs nearly the steel bar surface and the mecha-
nism with pure slip would not be possible [10]. If a steel bar is
Figure 1 – Beam geometry
Bonded
A
zone
LVDT
10
B
C
Hydraulic jack
Dimensions
A (cm)
B (cm)
C (cm)
37.5
65.0
18.0
56.0
110.0
24.0
< 16 mm
> 16 mm
5
D
5
E
LVDT
Steel hinge
D (cm)
E (cm)
13.0
32.5
19.0
51.0
Spreader beam
Longitudinal section
Cross section
F
F (cm)
10.0
15.0
G
Centroid of
compressive force
G (cm)
3.0
4.0
D
5
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