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Table 1: International design standards recommendation summary on SFRC for slender beams

DESIGN TYPE OF FIBRES FLEXURAL STRENGTH EVALUATION/ SHEAR MINIMUM MINIMUM SHEAR
STANDARDS DESIGN STRENGTH LONGITUDINAL REINFORCEMENT
EVALUATION / STEEL RELAXATION
STEEL OTHER COMP. TENSION DESIGN DESIGN RELAXATION
FIBRE FIBRES DESIGN STRESS- STRESS-STRAIN
STRAIN CURVE CURVE
AASHTO [9] ü – – – – – –
RILEM [7] ü – ü ü ü – –
ACI 318 [8] ü – – – – – ü
Fib [6] ü – ü ü ü – –
EC2 [10] ü – ü ü ü ü* ü
* Not applicable for beams

3. CRACKING IN SFRC DEEP BEAMS The ratio, V cr /V cr _AASHTO was plotted using a box and whisker
plot in Figure 2 for various ranges of modified fibre factor, F’
SFRC members can resist significant tensile stress across cracks given by α f V f , where V f is the volume fraction of fibres, α f is the
[5]
due to the bridging action of fibre . This results in distributed aspect ratio of fibre (= l f /d f ); l f and d f are length and diameter of
shear cracks of lesser crack widths [5,18-19] . Also, the tensile
fibre, respectively. The modified fibre factor (F’) accounts for the
strength of concrete is slightly greater in the presence of fibres two main influencing parameters related to fibres: aspect ratio
causing the delayed first shear crack [5,18,20-21] . At higher load (α f ) and volume fraction (V f ) . It is observed that there is scatter
[29]
levels, vertical stirrups are observed to have more influence on
in data (with a coefficient of variation of around 0.31), possibly
controlling diagonal crack widths . The post-cracking stiffness due to the inherent variability in FRC concrete and observational
[5]
was also observed to be higher for SFRC beams attributed to error in diagonal cracking load. A gradual increase in diagonal
smaller crack widths.
cracking load is observed, with increase in fibre factor, with an
The addition of fibres was found to be very effective in reducing average increase of around 23 % for F’≈1. Therefore, providing
shear crack widths (up to about 11 %) . Crack widths depended steel fibres is beneficial in delaying diagonal shear crack.
[5]
on the dosage of fibres and the amount of crack control
reinforcement. Addition of steel fibres in deep beams could 4. STRENGTH AND DUCTILITY OF SFRC DEEP
replace the minimum code specified distribution reinforcement BEAMS
[18]
as observed from experimental studies . It is observed that
the fibre volume fraction of 0.5 % could replace the minimum The strength of deep beams depends on concrete strength,
specified 0.3 % of distribution steel in AASHTO code , with an shear span-depth ratio, percentage of reinforcement and also
[9]
equivalent serviceability performance . However, a fibre volume on loading configuration. Strength of deep beams can be
[22]
ratio of more than 0.5 % did not have a significant effect on enhanced by adding an appropriate amount of fibres primarily
[22]
reducing crack widths . due to increased biaxial strength, delayed formation and growth
The experiments on 127 SFRC deep beams with shear span to 5
depth ratios less than 2 are collected from literature [6,18-20,23-28] . 4.5
The details of the specimens are given in Appendix 1. Out of the 4
collected data, experimentally observed first diagonal cracking 3.5
shear, V cr for 106 specimens is normalized using the expression 3
for diagonal cracking shear, V cr , AASHTO provided in AASHTO /V cr _AASHTO 2.5
code given by, 2
[9]
V cr 1.5
1
(2) 0.5
0
F’
F’
where f c ’ is in MPa, b and d are in mm, V cr , AASHTO is in N, a is the F’= 0 0.25<=F’<=0.5 0.5< <=0.75 0.75<F’<=1 1< <=1.25
shear span and d is the effective depth. Figure 2: Plot of normalised first diagonal cracking load with fibre factor

14 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026