Literature Survey on Shear in FRC Beams - On Shear Behavior of Structural Elements Made of Steel Fiber Reinforced Concrete - page 26

3.9 Combination of Steel Fibers and Stirrups

The addition of bers to conventional stirrups leads to the following effects:

Crack spacing: Cracks are less separated due to the presence of bers. As a

consequence, a smaller characteristic length ( L r ) should be used [ 49 ].
Shear strength: Steel bers improve the shear resisting mechanism of the

concrete represented by the aggregate interlocking and dowel action so, the shear
strength signicantly increases [ 27 , 29 , 63 ]. Fibers can also be combined with
stirrups, in this situation, the stresses in the stirrups are reduced [ 29 ].
Crack control: Fibers control the cracking process alone or in combination with
stirrups [ 62 , 72 ].
Stresses in stirrups and bers: Fibers retarded the appearance of inclined
cracks and, consequently, the stirrups are tensioned later [ 34 ]. At the same time,
when stirrups and

bers work together, a further reduction in the working stress of

bers can be observed [ 34 , 39 , 61 , 73 , 74 ]. Other bene t of the combinations of

ber can reduce the amount of stirrups required satisfying
strength and ductility requirements [ 9 ].

bers and stirrups is that

3.10 Shear Models and Design Codes

3.10.1 Design Codes

The current Design Codes to determine shear strength of structural elements made
with FRC are basically, the RILEM approach [ 75 ] and the MC2010 [ 2 ]. RILEM has
evolved, having presented different versions up to the current formulation. Firstly,
RILEM approaches used equivalent

fl exural tensile strengths up to the current version

which uses residual fl exural tensile strengths according to the Standard EN 14651.

3.10.1.1 Previous Versions of RILEM Approach

Original RILEM Design Method

The original RILEM design method [ 74 , 76 ] calculated the shear capacity (V)as
consisting of 3 separate contributions:

V=V c +V s +V f ð 3 : 9 Þ

where:
V c shear resistance of the member without shear reinforcement

V s contribution of the shear reinforcement (stirrups and/or inclined bars)

V f contribution of steel ber shear reinforcement.