Civil Engineering Reference
In-Depth Information
Fig. 6.8 Shear crack
evolution (failure mode III)
concretes with
ϕ
6 stirrups showed a very brittle post-crack behavior, while beams
with BN
bers
and reinforced beams reached the highest loads. Beams with traditional shear
reinforcement show an important de
bers were the most ductile. For all strength levels, beams with BP
fl
ection increase just after the
rst crack and a
greater load reduction after peak.
From those shear tests: load, de
ection and crack widths were measured. Also,
cracking pattern was observed by means of pictures and video recording.
Figure
6.9
shows the load-de
fl
fl
ection response of all tested beams. The maximum
loads are reported in Table
6.3
.
Shear cracks widths development during the test was analyzed by analysis of
pictures coordinated with loading process through the time (Fig.
6.10
). In the load-
de
ection curves, the point markers indicate the maximum shear crack width for its
corresponding load-de
fl
ection value. It can be noticed that at shear peak load, the
shear crack opening was about 0.2 mm.
Observing Fig.
6.10
,
fl
the beam with stirrups (H
ϕ
6) achieved the greatest
de
fl
ection (at midspan) at the peak load and reached higher de
fl
ection, if compared
with SFRC. The beam with BN
bers obtained crack widths slightly smaller for the
same de
bers. Obviously, the beam
without any reinforcement had a completely brittle behavior.
In the Sect.
6.3
of this chapter, it was obtained that toughness properties of the
FRC depended not only of the type of
fl
ection, as compared to the beam with BP
bers, but also with the compressive strength
of the concrete. For that, it was determined a new parameter f
Rm
=(f
R1
+ f
R3
)/2. After
having the test results of the beams, it is intended to know if there is a relationship
between the toughness properties (using shear stress
, determined with f
R3
and f
Rm
)
and the experimental shear value (V
test
in kN) and, which toughness value (f
R3
or f
Rm
)
represents better the shear behavior to be included in the design Codes. Therefore,
Fig.
6.11
shows the experimental shear strength versus the
˄
“˄”
factor proposed by
RILEM [
13
](
f
R3
) and, in Fig.
6.12
, the same tendency was
analyzed but using an average residual
τ
= k
f
·
0.7
· ʾ ·
0.18
·
fl
exure tensile strength f
Rm
=(f
R1
+ f
R3
)/2
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