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TECHNICAL PAPER

(a) (b)
Figure 10: Comparison of normalized observed shear strengths: (a) Longitudinal to transverse steel ratio; (b) Shear span-depth ratio

5.5 Effect of steel reinforcement ratios exceeding 2.2, whereas the test results of the present study
correspond to the beams having a/d ratios between 1.05-1.7.
In order to investigate the influence of steel reinforcement ratio The shear strengths of test specimens except L550-ST600
on the shear strength of concrete beams, test results published were higher than the maximum shear strengths allowed by
in the ACI-DAfStb Databases [26-27] , the findings of the two the ACI 318-19 . Thus, it was concluded that the current code
[3]
recent studies [6,16] , and the test results of the present study were provisions are conservative and adequate for the shear design of
considered for the comparison. Tests results of beams reinforced concrete beams having low a/d ratios and reinforced with high-
with the longitudinal steel of yield strengths in the range of strength steel reinforcement.
420-815 MPa and the transverse steel of yield strengths ranging
between 420-641 MPa were selected. The goal was to study 6. CONCLUSIONS
the influence of high-strength steel reinforcement on the shear
strengths of concrete members. Steel reinforcement ratio was Based on the test results, the following major conclusions can be
defined as the ratio of the percentage of longitudinal steel times drawn:
their yield strengths ( ρ st f yl ) to the percentage of transverse steel
times their corresponding yield strengths (ρ sv f yv ). 1) All beam specimens reinforced with the high-strength
steel as longitudinal and transverse reinforcement resisted
Figure 10(a) shows the variation of normalized shear strength significantly higher peak shear loads as compared to their
′
(V exp c f bd ) with the steel reinforcement ratio respective design strengths. The measured peak shear
( ρ st f yl /ρ sv f yv ) of test specimens. All specimens showed the shear loads were found to be 4.0 times the design shear strengths
strengths equal to or higher than the design shear strength of predicted using ACI 318-19 and IS: 456 (2000) provisions
[2]
[3]
0.17 f bd as per ACI code for all values of steel reinforcement for beams having the shear span-to-depth (a/d) ratio of
[3]
′
c
ratios. The higher shear strengths were noted for the concrete 1.05. The concrete strut action being predominant led to
beams having very low steel reinforcement ratios. The peak higher difference between the measured and design shear
shear loads in test specimens having a/d ratios less than 1.7 strengths of beams with low a/d ratios. This also highlighted
exceeded the maximum shear strengths of 0.85 f bd as per the the enhanced shear strength of concrete beams in sections
′
c
ACI code . As the steel reinforcement ratios were increased, near to supports.
[3]
the normalized shear strengths were found to be reduced. All
data points of the present study (having the steel reinforcement 2) Beams with a low grade of concrete and reinforced with Fe-
ratios ~ 8.7-9.4) except for the specimen L550-ST600 were found 500D grade longitudinal steel failed in the diagonal shear, as
to lie above the results of past studies. This is primarily due to expected, for all grades of transverse steel with a maximum
the low a/d ratios of the specimens tested in this study resulting yield strength of 600 MPa. However, the beam specimens
in the higher normalized shear strengths. Figure 10(b) shows the with high concrete compressive strength and Fe-550D grade
variation of the normalized shear strengths with the a/d ratios longitudinal steel failed in flexure mode even though they
of test beams. All previously tested beams had the a/d ratios were designed to fail in the diagonal shear. This showed

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