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Title: Post-Cracking Stiffness Model of Solid and Hollow GFRP-Reinforced Concrete Members under Torsion

Author(s): Ibrahim T. Mostafa, Salaheldin Mousa, Hamdy M. Mohamed, Brahim Benmokrane

Publication: Structural Journal



Appears on pages(s):

Keywords: box girders; effective wall thickness; glass fiber-reinforced polymer (GFRP) bars; high-strength concrete (HSC); normal-strength concrete (NSC); post-cracking torsional stiffness; reinforced concrete; spirals; steel reinforcement; ties; twist behavior; ul

DOI: 10.14359/51740483

Date: 1/24/2024

Although estimating the post-cracking torsional stiffness is vital for distributing the torsional moment in analyzing statically indeterminate reinforced concrete (RC) structures, none of the North American codes provide an analytical approach for determining the torsional stiffness after cracking. Moreover, the scarcity of experimental work has resulted in the lack of torsion design provisions for concrete box girders reinforced with glass fiber-reinforced polymer (GFRP). Therefore, the purpose of this research was to study the stiffness characteristics of RC box girders reinforced with GFRP reinforcement and to provide a simple analysis technique that can be used to predict post-cracking torsional stiffness. Fourteen concrete box girders were fabricated and tested under a pure torsional moment. In addition, data on 10 solid rectangular RC beams with GFRP reinforcement was collected from the literature. The test results indicate that the concrete strength, as well as the ratio, type, and configuration of the web reinforcement, substantially affected the post-cracking torsional stiffness of the tested specimens. An analytical model was developed for estimating the torsional stiffness after cracking. This model was based on a thin-walled tube and space truss analogy using a concept of post-cracking shear modulus. The proposed model considers the effect of concrete strength, the configuration and ratio of the GFRP web reinforcement, and the ratio of the GFRP longitudinal bars. In addition, an equation to calculate the ultimate twist of the GFRP-RC members was developed. The validity of the proposed model was investigated by analytically regenerating the torque–twist curves of the tested box girders and the other specimens available in the literature.