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IBRACON Structures and Materials Journal • 2012 • vol. 5 • nº 6
M. N. KATAOKA
| M. A. FERREIRA
| A. L. H. C. EL DEBS
maximum load determine in their project, which was 150 kN. This
performance can be attributed to the design details and to the
care taken during the construction of the models. In order to im-
prove the connection behavior, a greater number of stirrups at
the ends of the beams were concentrate, minimizing the cracking
and avoiding the slippage between the precast concrete and the
cast on site concrete.
The stirrups height was higher than it is usually determined in a
project which is the same height of the beam. In the models the
stirrups reached the concrete cover of the slab, where the con-
tinuity reinforcement was located at the same level. This detail
was used to distribute the stress between all bars. The trans-
verse reinforcement was used to reduce the stress in the connec-
tion and to distribute the cracks. In Model 2, the cracking began
on the beams and not in the connection as usual.
In the construction of the bending moment
versus
rotation curve
was used the average of the rotations and the bending moments
of the right and left sides. Comparing the curves of the two mod-
els, Model 2 presented experimental stiffness higher than Model
1, the difference reached 65%. Comparing the secant stiffness,
this difference between the models was lesser, about 22%. Fig-
ure 12 shows the bending moment
versus
rotation curves for
comparison between the behavior of Model 1 and 2. Table 2
contains the values of secant stiffness and project stiffness for
Models 1 and 2.
Three types of rotation measurement were performed during
the tests in order to examine the most appropriate. All methods
used (transducers, clinometers and extensometers with re-
movable base) provided similar values, and the data obtained
by clinometers was used in the construction of the bending
moment
versus
rotation curves. Figure 13 presents the load
versus
rotation curves for each measurement method to com-
pare the results.
For each model, the force
versus
strain curves of the continuity
reinforcement were drawn based on the average values of steel
bars strain. It was possible because there were no differences
between the behaviors of the bars. Comparing the curves in
Figure 14, the difference between the connections behavior can
be note because for the same reinforcement ratio and the same
load, in some situations Model 1 showed high strain, up to 100%.
This fact may have occurred because Model 2 had slab and the
stresses were distributed in a larger number of bars, despite hav-
ing the same steel area of Model 1.
Figure 13 – Load
versus
rotation curves for the three methods of rotation measurement
Figure 14 – Load
versus
strain in the
continuity reinforcement curves