Shear resistance of reinforced concrete beams with and without steel fibres.

The fabrication and placement of conventional shear rein-
forcement are time consuming and costly and
its use
in thin structural
concrete members
is often
impractical. Fibre
reinforcement
is known
to control
flexural and shear cracking and can therefore be used to
replace conventional shear reinforcement. This investigation consists
of experimental and theoretical studies
into the use of crimped steel
fibres as shear reinforcement in
reinforced concrete beams.
Eighteen reinforced
lightweight
concrete beams with
thin
web were
fabricated and
tested under
four point
loading. The para-
meters studied were
the fibre content,
the shear span/effective depth
ratio and
the amount of main steel. Subsidiary tests on concentric
pull-out specimens and shear
transfer specimens were carried out to
study-
the influence of
steel
fibres on
the bond stress slip characteristics
of a deformed bar (Tor Bar) and the stiffness and ultimate
strength of
the shear-transfer
mechanism across
a definite
plane respectively.
The inclusion of
fibres increased the ultimate strength of
the beams by 63 to 211.5%. Fibre concrete beams had more
flexural and shear cracks and showed substantially greater ductility
at
failure than their plain concrete counterparts. The fibres in
the pull-out specimens were effective
in controlling the splitting
cracks and
transforming a sudden bond failure into a gradual one.
The fibres increased the ultimate shear strength of the shear
transfer specimens by 9.9 to 101.8%. The stiffness of the shear
transfer mechanism was not, however, significantly affected.
A simple approach based on
the Standard Method of the
CEB-FIP Model Code is proposed to determine
the ultimate shear
resistance of
fibre
reinforced concrete beams.
It predicts
adequately
the ultimate shear strength of steel
fibre
reinforced concrete beams.
A nonlinear 3-dimensional finite element model was
developed to predict the entire structural response up
to failure
of both plain and
fibre
reinforced concrete beams subjected
to
short_.
term monotonically
increasing loading. The concrete
is
represented by 8-nodeisoparametric hexahedra and
the tension steel
by bar elements. The finite element model predicts satisfactorily
the structural behaviour of both plain and
fibre
reinforced
concrete beams.