Shear Strength of Reinforced Concrete T-Beams without Transverse Reinforcement

The authors have presented an interesting paper on the
shear strength of reinforced concrete T-beams without
transverse reinforcement. However, the discusser would like
to offer the following comments:
1. The authors have mentioned the basic outline of a
derivation of Eq. (1), but Eq. (1) appears to be based on the
neutral axis (NA) located at the center of the beam in a
typical homogeneous rectangular concrete beam. The
authors’ Eq. (2) was a simplification of Eq. (1) based on the
experimental database of reinforced concrete beams, which
is inconsistent with the Rankine’s failure criteria of a plain
homogeneous concrete beam.
Based on ft
= 6 (or 0.1fc ′ ) and assuming the Rankine’s
failure criteria of plain concrete, and by considering various
strength ratios of flexural stress σm versus concrete compressive
stress fc ′ (σm/f ′
c
= 14.2%,
10 the flexural stress σm of a plain
homogeneous concrete beam equals to 114.2%10
of the tensile
strength of plain concrete ft
. Based on the aforementioned
assumptions, the discusser arrived at the authors’ Eq. (2)
without considering the experimental database of reinforced
concrete beams.
Another simplified approach is that Eq. (2) can also be
derived from the current ACI Building Code9
(that is,
authors’ Eq. (5)) by assuming an average depth of NA equals
0.4d11,12
and by substituting c = 0.4d in the authors’ Eq. (5),
which would result in authors’ Eq. (2). Based on the afore-
mentioned two approaches, the discusser believes that there
is no need to have a reinforced concrete beam database, that
is, Fig. 1 and 2. Is this consistent with the shear strength of
reinforced concrete T-beams without transverse reinforce-
ment plain concrete?
fc ′
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