Torsional Behavior of Reinforced Concrete Beams with High-Strength Steel Bars

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Title: Torsional Behavior of Reinforced Concrete Beams with High-Strength Steel Bars

Author(s): C. Kim, S. Kim, K.-H. Kim, D. Shin, M. Haroon, and J.-Y. Lee

Publication: Structural Journal

Volume: 116

Issue: 6

Appears on pages(s): 251-263

Keywords: high-strength reinforcement; reinforced concrete beam; torsional reinforcement; torsional strength

Date: 11/1/2019

Abstract:
In the design of reinforced concrete (RC) structures, members subjected to shear and torsional moments are generally designed from a nearly identical design viewpoint. Therefore, most widely used design codes limit the maximum yield strength of shear and torsional reinforcements to the same level. Recent studies on the shear behavior of RC members using high-strength reinforcement suggest that the use of high-strength shear reinforcement can meet the design requirements for failure mode, shear capacity, and usability of high-strength steel. According to this design criterion, high-strength steel that can be applied to shear strengthening can also be used as torsional reinforcement, and the application has to be verified based on the experiments. However, current studies on the torsional behavior of RC members designed with high-strength torsional reinforcement seem insufficient. The shear and torsional moments cause the same shear stress effect, but if the members are subjected to bending moments in the presence of shear and torsion, the resulting effective compressive stress in a web of members can vary. Unlike the shear failure, the member subjected to torsion showed the concrete failure in the corner-joint region of the three-dimensional space-truss model. In this study, a total of 29 RC beams reinforced using normal and high-strength torsional reinforcement were tested under torsion. The main variables were the amount and yield strength of torsional reinforcement. Torsional failure modes and maximum strengths were analyzed, and the feasibility of using high-strength torsional reinforcement in RC members subjected to torsion was evaluated based on the test results. Furthermore, additional test results of RC members subjected to torsion from the previous studies were also analyzed. The test results indicate that most of the high-strength torsional reinforcement did not reach their yield strength, and when the yield strength of torsional reinforcement exceeded 80 ksi (550 MPa), the torsional capacity was lower than the design strength.