Page 4 - ICJ Feb Openaccess 2026

TECHNICAL PAPER

STRENGTH AND SERVICEABILITY

EVALUATION OF STEEL FIBRE

REINFORCED DEEP BEAMS: BIJILY BALAKRISHNAN*

A REVIEW INDU GEEVAR
ABINS AZIZ
AYSHA ZENEEB MAJEED

Abstract ‘Disturbed regions’ (‘D’ regions) occur in members with load or
[2]
geometric discontinuity , due to the presence of concentrated
The applications of steel fibre reinforced concrete (SFRC) loads or geometric irregularity causing a disturbance in the
are limited in deep members, due to a lack of well-defined stress path. As per St Venants principle, ‘D’ region extends up to
guidelines for design of such members. The present study one member depth of the member. ‘D’ regions are encountered
evaluates the effect of steel fibres on strength, crack width and in deep beams, corbels, pile caps, pier caps, beam-column
first shear cracking load using available experimental data on joints, transfer girders etc. [Figure 1(a)], where the strut-and-tie
127 SFRC deep beams with a shear span-to-depth ratio less than method is commonly used for design [2-5] . Strut-and-tie method
two. The study shows an average increase in strength and the idealizes the region as a hidden truss with concrete struts and
first diagonal cracking load of 37 and 23 %, respectively for a steel ties , capable of supporting the external loads. The
[2]
fibre factor of 1. The data shows significant scatter, possibly due beams with a shear span to depth ratio of less than 2, can be
to inherent variability of SFRC. Nevertheless, SFRC deep beams considered a deep beam, as the whole region can be classified
are effective in crack control and exhibit good ductility response, as ‘D’ region. These beams behave differently compared to
and a reduction in distribution reinforcement is possible. The slender flexural members . The load-carrying mechanism of
[2]
study also summarises the existing models for shear strength these members is predominantly by ‘strut action’, where the
prediction of SFRC deep beams and three recent models are load gets directly transmitted to the supports, with the help
[2]
used for a comparative study. The study suggests strut-and-tie of main tie reinforcement . Apart from main reinforcement,
based model considering the contribution of fibres for design of distributed reinforcement consisting of a mesh of vertical and
SFRC deep beams. horizontal reinforcement is provided in the shear span primarily
to control crack widths at service loads and also to provide
Keywords: Crack width, Deep beam, Fibre reinforced concrete, sufficient ductility . Figure 1(c) shows the typical detailing of a
[2]
Shear strength, Steel fibre, Strut-and-tie method. deep beam. Transfer girders in buildings are examples of deep
beams intended to provide large column-free space beneath
1. INTRODUCTION [Figure 1(a)]. SFRC may be adopted to provide crack control and
ductility in these members.
Steel fibre-reinforced concrete (SFRC) is developed by the
addition of steel fibres to conventional concrete to enhance its This paper presents a critical review of the use of SFRC in deep
[1]
material properties . The addition of steel fibres can result in beams. The study of existing international design codes shows
significant reduction in the usage of steel as reinforcement in that there is lack of sufficient guidelines with respect to the
reinforced concrete (RC) structures and reduces the overall cost use of SFRC in deep beams [6-10] . The paper presents available
[1]
of construction, especially in large-scale projects . experimental data on 127 SFRC deep beams with a shear span-
to-depth ratio less than two and quantifies the effect of steel
The existing studies on SFRC primarily focus on the applicability fibres on first diagonal cracking loads, crack widths, and ultimate
in flexure dominated members structural members, such as shear strength. The fibre contribution on the ductility of deep
precast tunnel segments, elevated flat slabs, reinforced earth- members is also studied. The study also summarises some of
retaining walls, and ground-supported flat slabs . However, the analytical models available in the literature describing the
[1]
not much research has been done on applications of SFRC in parameters involved and principle followed in those models.
‘disturbed regions’ (‘D’ regions), where the Bernoulli’s hypothesis The applicability of three recent models is compared with
of plane sections remaining plane after bending is not valid. experimental data and suitable conclusions are presented.

12 THE INDIAN CONCRETE JOURNAL | FEBRUARY 2026
* Corresponding author: Bijily Balakrishnan, Email: bijily@iittp.ac.in