Page 5 - June-2022

TECHNICAL PAPER

and the high-performance (HP) steel (yield strength = 690 MPa) The present study investigates the suitability of high-strength
conforming to ASTM 1035-07 as the shear stirrups of the same steel as shear reinforcement in concrete beams of low shear
[7]
longitudinal spacing. The enhancement in shear strength and span ratios experimentally. The main objective of this study is to
reduction in shear crack width was noted in beams reinforced investigate the influence of the grade of concrete and the grade
with the HP steel. As the failure of these beams was controlled of reinforcing steel on the shear behavior of concrete members.
by the crushing of the concrete strut, it was suggested that the This study presents the results of six concrete beams reinforced
yield strength of HP steel should be limited to 550 MPa in the with high-strength steel as the longitudinal as well as transverse
design of shear reinforcement. Subsequent tests by Munikrishna reinforcement tested up to failure. Two different grades of
et al. confirmed that the width of shear cracks in the concrete concrete representing the normal-strength and high-strength
[8]
beams with the HP steel as shear stirrups was within the concrete are used in the test specimens. The influence of the
allowable limits. Lee et al. concluded that the compressive shear span-depth (a/d) ratio, the type of longitudinal as well as
[9]
strength of concrete in RC beams had a strong influence on the transverse reinforcing steel, and the spacing of stirrups on the
utilization of high-strength shear stirrups. The yield strength of shear behavior of beams have been investigated.
shear reinforcement beyond 600 MPa may not be fully utilized
when used in normal-grade concrete beams. The increase 2. RESEARCH SIGNIFICANCE
in the yield strength reduces the shear redundancy and the
effectiveness of high-strength shear reinforcement. The efficient use of high-strength material has the potential
to provide durable, sustainable, and economical concrete
A significant reserve strength has been observed in the concrete members in high-rise structures with higher available floor
beams reinforced with high-strength steel after diagonal area and reduced maintenance requirements. However, the
cracking. The failure of concrete struts was observed at the full strength of high-strength steel is not utilized in the shear
higher load levels for the beams reinforced with high-strength design of concrete members because of serviceability concerns
steel compared to those with conventional steel [10] . Further, the owing to the crack width limitations. The present study provides
shear behavior of concrete beams is strongly dependent on experimental evidence of the strength and serviceability of
the shear span-to-effective depth (a/d) ratios. An experimental concrete beams reinforced with high-strength steel having
study conducted on high-strength concrete columns with yield strengths in the range of 500-600 MPa. The influence of
high-strength steel showed that shear failure occurred before the yielding strength of reinforcing steel and the compressive
the yielding of longitudinal reinforcement bars [11] . Further, the strength of concrete on the shear behavior of concrete beams
shear reinforcement bars did not yield at the peak applied load has been demonstrated. Particularly, the shear behavior of
of columns. The increase in member depths and the decrease concrete beams with low shear span-depth (a/d) ratios has been
in aggregate size may result in the reduction in shear stress at highlighted. Test results are compared with the design strengths
the failure of concrete members [12-13] . The average width of the predicted using the provisions of different building codes. This
shear crack may exceed the allowable limits of ACI 224R-01 [14] study provides valuable information for updating the shear
for the concrete beams of larger cross-sections and the higher design provisions in the building codes.
amount of shear reinforcement [15-16] . Further, the concrete beams
with low shear span-depth (a/d) ratios have exhibited either 3. EXPERIMENTAL INVESTIGATION
compression strut failure or shear compression failure [17] . In
such cases, the high-strength shear reinforcement may not yield An experimental program has been undertaken in this
before the maximum shear strength is reached. study to investigate the behavior of RC beams subjected to
monotonically increasing lateral loads. The details of test
Despite numerous past studies on high-strength steel as shear specimens, material properties, test setup, and instrumentations
reinforcements, there is a lack of consistency in the shear design are presented in the following sections.
of RC beams worldwide. The Eurocode-02 [18] limits the design
yield strength of shear reinforcement to 600 MPa for all grades 3.1 Test specimens
of concrete, whereas the Japanese Guidelines for Concrete [19]
allow the yield strength of shear reinforcement to reach up to Six number of reinforced concrete (RC) beams of two different
800 MPa, when the compressive strength of concrete is greater concrete grades and three types of reinforcing steel were tested
than 60 MPa. Past experimental studies have mostly focused on in this study. The type of steel includes the high-strength rebars
the concrete members having the a/d ratios exceeding a value of Fe-500D, Fe-550D, and Fe-600 grades conforming to the
of 2.0. However, very limited research has been conducted on IS:1786 (2008) [20] specifications. The designation of steel grade
concrete members having low a/d ratios and reinforced with denotes the minimum specified yield strength of steel in MPa.
high-strength transverse reinforcement. For example, the grade Fe-500D represents the reinforcing bars

THE INDIAN CONCRETE JOURNAL | JUNE 2022 15