B. Espion et al., ON THE USE OF STEEL FIBERS AS COMPLEMENTA RY REINFORCEMENT OF REINFORCED-CONCRETE BEAMS IN BENDING, Materials and structures, 26(162), 1993, pp. 479-485
Citations number
7
Categorie Soggetti
Engineering, Civil","Material Science","Construcion & Building Technology
This paper reports the results of experimental research focusing on tw
o possible methods to enhance the service load behaviour of ordinary r
einforced concrete structural elements, i.e. the use of steel-fibre co
ncrete and the use of high-strength concrete. The programme involved t
he testing of nine reinforced concrete beams with rectangular cross-se
ction (b = 25 cm, h = 15 cm) and span L = 140 cm. The reinforcement ra
tios considered (rho = 0.33, 0.52 and 0.75%) are usual for slabs,for w
hich the deflection limit state may often become a design factor. For
each reinforcement ratio, we tested a beam in ordinary concrete (BN; 3
2 MPa), a beam in high-strength concrete (BHP; 60 MPa) and a beam in f
ibre-reinforced concrete (BF; 38 MPa; fibre content 0.4 vol%). We also
tested a fibre-reinforced concrete beam with no bar reinforcement (BR
F; rho = 0) to determine the material properties of fibre concrete tha
t we needed to compute the carrying capacity of the BF beams. Test res
ults show that the use of high-strength concrete seems more effective
than the use of fibre concrete to reduce the deflections at service lo
ad level. BF beams are slightly stiffer than the BHP beams for higher
loading levels (stabilized cracking phase of BN and BHP beams)for the
two lowest reinforcement ratios. The carrying capacity of the BF beams
is greater than the carrying capacity of the BN beams; the difference
in carrying capacity may be estimated on the safe side with a simple
prediction model, and is significant (experimentally 32%) for the lowe
st reinforcement ratio. However, the ultimate load behaviour of the BF
beams is far less satisfactory than the ultimate load behaviour of th
e BN and BHP beams. For the BF beams, we observed the concentration of
all inelastic deformations at failure in a single cracked section and
the ductility factor varied between 1 and 2.8 compared with 4.5-6.3 f
or the BN beams and 8.7-10.6 for the BHP beams. The ultimate load beha
viour of the BHP beams was quite satisfactory, with the largest number
of cracks equally spaced and equally open and the largest deformation
capacity. We conclude from these tests that the tensile properties of
cracked fibre-reinforced concrete are too limited to reach the level
of deformation that is required in safe reinforced concrete design and
that the use of steel fibres as complementary reinforcement of rebars
should be avoided.