Torsional Behavior of High-Strength Concrete Beams with Minimum Reinforcement Ratio

Changbin Joh,Imjong Kwahk,Jungwoo Lee,Byung-Suk Kim,In-Hwan Yang

doi:10.1155/2019/1432697

Abstract

Although there is a growing trend to use higher strength for concrete and steel in reinforced concrete structures due to the lightness and slenderness of these members together with the simplified arrangement of their reinforcement, there is still the necessity to inspect the reduction of ductility resulting from the gain in strength. Taking into account that this also concerns the design for torsion, this study intends to investigate the regulations related to the torsional minimum reinforcement ratio in view of the minimum ductility requirement with focus on Eurocode 2. To that goal, the relation between the torsional cracking moment and the ductile behavior is discussed for the beam reinforced with the minimum torsional reinforcement ratio to examine the eventual properness of the minimum torsional reinforcement ratio recommended by Eurocode 2. Moreover, a pure torsion test is performed on 18 beams made of 80 MPa concrete reinforced by high-strength bars with rectangular section and various test variables involving the minimum torsional reinforcement ratio, the transverse-to-longitudinal reinforcement ratio, and the total reinforcement ratio. As a result, for the high-strength concrete beams, the minimum torsional reinforcement ratio recommended by Eurocode 2 was insufficient to prevent the sudden loss of strength after the initiation of the torsional cracking. But with regard to the compatibility torsion of statically indeterminate structure, the adoption of the minimum torsional reinforcement ratio recommended by Eurocode 2 might secure enough deformability under displacement-controlled mode to allow the redistribution of the torsional moment.

Highlights

There is a growing trend to use higher strength for concrete and steel in reinforced concrete structures due to the lightness and slenderness of these members together with the simplified arrangement of their reinforcement, there is still the necessity to inspect the reduction of ductility resulting from the gain in strength
Taking into account that this concerns the design for torsion, this study intends to investigate the regulations related to the torsional minimum reinforcement ratio in view of the minimum ductility requirement with focus on Eurocode 2
Based upon their experimental results, these authors reported that the postcracking strength, i.e., the ductile failure mode, depended significantly on the total reinforcement ratio in the longitudinal and transverse directions as well as the ratio of the longitudinal to the transverse reinforcement. is dependency was more marked in the high-strength concrete members than in those made of normal concrete

Summary

Minimum Torsional Reinforcement Ratio and Torsional Cracking Moment

Code provide conceptually identical minimum torsional reinforcement, this study analyzes theoretically the relation between the minimum torsional reinforcement and the torsional cracking moment (Tcr) with reference to EC 2. If ρv,min is accepted in the usual way as the minimum reinforcement ratio enabling the member to maintain ductility without sudden loss of the torsional strength after cracking, Tcr Tn and the following equation is obtained by equaling Equations (3) and (4): Tcr. If the beam is not prestressed and is reinforced in the transverse and longitudinal directions, the crack angle θ can be assumed to be 45°. It appears that the minimum reinforcement ratio ρv,min must be 2 to 3.7 times the value required by EC 2 to satisfy the condition Tcr Tn. is indicates that the application of the current ρv,min recommended by the design codes presents high risk of strength loss to occur after the initiation of torsional cracking

Torsion Test

D10 D13 D16 D19 D22

Test Results and Discussion

Torsion-Displacement Behavior