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Punching Shear Behavior of Two-Way Slabs Reinforced with High-Strength Steel

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The punching shear behavior of slabs reinforced with high-strength steel reinforcement was studied and compared with that of slabs reinforced with conventional steel reinforcement. The high-strength steel selected for this research conforms to ASTM A1035-07. The influences of the flexural reinforcement ratio, concentrating the reinforcement in the immediate column region, and using steel fiber-reinforced concrete (SFRC) in the slab on the punching shear resistance, post-cracking stiffness, strain distribution, and crack control were investigated. In addition, the test results were compared with the predictions using various design codes. The use of high-strength steel reinforcement and SFRC increased the punching shear strength of slabs, and concentrating the top mat of flexural reinforcement showed beneficial effects on post-cracking stiffness, strain distribution, and crack control. [PUBLICATION ABSTRACT]

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									 ACI STRUCTURAL JOURNAL                                                                                     TECHNICAL PAPER
Title no. 107-S47


Punching Shear Behavior of Two-Way Slabs Reinforced
with High-Strength Steel
by Jun-Mo Yang, Young-Soo Yoon, William D. Cook, and Denis Mitchell

The punching shear behavior of slabs reinforced with high-strength            Hassan et al.6 tested concrete beams reinforced with high-
steel reinforcement was studied and compared with that of slabs               strength steel without web reinforcement, and stated that the
reinforced with conventional steel reinforcement. The high-strength           shear strength of concrete beams reinforced with ASTM
steel selected for this research conforms to ASTM A1035-07. The               A1035 steel was significantly higher than that of companion
influences of the flexural reinforcement ratio, concentrating the             beams reinforced with Grade 420 MPa (60 ksi) steel, despite
reinforcement in the immediate column region, and using steel
fiber-reinforced concrete (SFRC) in the slab on the punching shear
                                                                              the reduction in the reinforcement ratio of 40%. Sumpter et
resistance, post-cracking stiffness, strain distribution, and crack           al.3 concluded that the direct replacement of conventional
control were investigated. In addition, the test results were                 Grade 420 MPa (60 ksi) stirrups with ASTM A1035 steel
compared with the predictions using various design codes. The use             stirrups increased the shear load capacity of flexural
of high-strength steel reinforcement and SFRC increased the                   members and enhanced the serviceability. There has been no
punching shear strength of slabs, and concentrating the top mat of            research on the punching shear behavior of two-way slabs
flexural reinforcement showed beneficial effects on post-cracking             reinforced with high-strength steel, however.
stiffness, strain distribution, and crack control.                               There are many variables that affect the punching shear
                                                                              behavior of two-way slabs, including concrete strength,
Keywords: cracking; fiber-reinforced concrete; high-strength reinforcement;   reinforcement ratio, the arrangement of the flexural reinforce-
punching shear; slabs; stiffness.
                                                                              ment, the use of fiber-reinforced concrete (FRC), and
                                                                              effective depth (size effect). It is obvious that the shear stress
                        INTRODUCTION                                          at punching shear failure increases with increasing concrete
   The efforts to achieve high-performance, durable reinforced                strength. The code expressions of ACI 318M-087 and CSA
concrete structures have increased the demands for                            A23.3-048 for two-way punching shear strength are a
improving the performance of both the concrete and the                        function of the square root of the concrete compressive
reinforcing materials. Recently, high-strength steel reinforcement            strength, whereas the expressions for the punching shear
conforming to ASTM A1035-071 has been developed to                            resistance of BS 8110-97,9 CEB-FIP MC 90,10 and Eurocode 211
satisfy those demands. This high-strength steel is more                       are a function of the cube root of the concrete compressive
corrosion resistant compared with conventional steel and has                  strength. Marzouk and Hussein12 and Gardner13 proposed
a yield strength that is almost twice that of conventional                    using a punching shear equation that is proportional to 3 f c′
normal-strength steel. The use of this steel provides greater                 rather than f c′ , but Mitchell et al.14 indicated that more
durability through the increased corrosion resistance of the                  experimental research is needed—particularly on high-
reinforcement and is particularly important for slab structures,              strength concrete slab-column connections—to enable the
such as parking garages subjected to deicing chemicals.                       development of design expressions for punching shear that are
There are several practical advantages to using this high-strength            applicable to a wide range of concrete strengths. The effective
steel, including a reduction of congestion in heavily reinforced              depth also affects the punching shear strength of slabs. As
members, savings in the cost of labor, and a reduction of                     the effective depth increases, the shear stress at punching
construction time.2,3 Without the necessary experimental                      failure decreases. Gardner13 and Mitchell et al.14 reported
evidence, however, there has been some reluctance to use                      that this size effect is significant and should be included in code
high-strength steel because of concerns about possible                        design expressions. The ACI Code7 does not account for the
excessive cracking and deflection that might not meet                         size effect, whereas the CSA Standard,8 BS Code,9 CEB-FIP
serviceability requirements.                                                  Code,10 and EC2 Code11 include factors for the influence of
   A number of research programs have been carried out to                     size effect on the punching shear resistance.
evaluate the performance of concrete members reinforced                          Many researchers have shown that the punching shear
with high-strength steel. Yotakhong4 demonstrated through                     resistance decreases with decreasing flexural reinforcement
the experimental testing of large-scale beams with different                  ratio, and the punching shear resistance expressions of BS
reinforcement ratios of high-strength steel that all test beams               8110-97,9 CEB-FIP MC 90,10 and Eurocode 211 account for
exhibited a ductile behavior with significantly strained steel                the reinforcement ratio as a factor affecting two-way shear
when the crushing strain of the concrete was reached.                         strength. Dilger et al.15 recommended that the influence of
Seliem5 conc
								
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