Experimental Tests - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 50

Part III
Experimental Tests

Contents of Part III

After making a thorough study of the literature on the shear behavior of structural
elements made of ber-reinforced concrete — FRC — (Chap. 3 ) and concrete without

bers, it is possible to detect some possible aspects to take a step that allows to
better understand the shear behavior of structural elements made with FRC.
In the literature it is not entirely clear the contribution of the ange size of

double-T beams to shear strength. In the current Codes, this effect does not appear
for the determination of shear strength in concrete without

fl

bers but it appears in
the RILEM guidelines for FRC. It seems of practical interest to better understand
whether or not the

ange helps to resist shear. To this aim, an experimental cam-
paign was carried out consisting of eight FRC prestressed beams and a concrete
without

fl

ange widths
(260, 400, and 600 mm); two of the nine beams had both stirrups and

bers was used as reference. The beams had different top fl

bers, one
was reinforced only with stirrups and the other six beams were reinforced only with

bers for shear resistance. As additional variable, one of the beams was done with a
larger ange (with an increase in height of 50 mm). Chapter 4 explains in detail the

experimental program: procedure, testing, data collection, analysis of results and
conclusions.
Today it is well known that the size of the beam has a clear in

fl

uence on the
shear strength of the element. As the depth of the element increases, the lower is the
shear strength achieved. This is due to the great in

fl

uence that exists between the
depth and the shear crack width. In large beams such opening is larger and this is
detrimental to shear capacity. Collins et al. came to the conclusion that longitudinal
reinforcement distributed along the beam depth could eliminate the size effect, as
the same happens if stirrups are added. The question raised was if

fl

bers could
mitigate somewhat the size effect or even eliminate it as the stirrups can do. In order
to give an answer to this question, an experimental program was carried out for
shear tests on nine large beams, where three beams had a depth of 500 mm, the next
three a depth of 1000 mm, and the last three had a depth of 1500 mm. In turn, each