Shear strengthening of concrete members with unbonded transverse reinforcement: Fid-Bau Portal

Shear strengthening of concrete members with unbonded transverse reinforcement

Fiset, Mathieu / Bastien, Josée / Mitchell, Denis

Highlights • Shear strengthening techniques with unbonded bars increase shear capacity. • The codes assuming perfect bond are not applicable for members with unbonded bars. • Finite elements modeling gave accurate predictions of the shear behaviour. • Propagation of a large diagonal crack is required to activate unbonded bars. • The anchor stiffness and the prestressing drive the shear resisted by unbonded bars.

Abstract This paper examines the behaviour of thick concrete members strengthened in shear with unbonded transverse reinforcement. The retrofitting technique consists of placing unbonded vertical bars with steel end plates or torque controlled expansion end anchorages in pre-drilled holes of existing thick members. To study the behaviour of these members, loading tests as well as numerical analyses were carried out. Shear capacities were compared to the predictions using the shear design approach in the Canadian Highway Bridge Design Code. The design equations which are intended for traditional stirrups reinforcement overestimates the shear capacities of the members strengthened with unbonded transverse reinforcement. However, numerical analyses provided very accurate predictions of the shear capacities. A finite element parametric study examines the effects of the shear span-to-depth ratio, vertical prestressing, shear reinforcement ratio and the stiffness of the vertical reinforcement. The stiffness of the shear strengthening system and the effects of prestressing significantly affect the shear capacity. The shear capacities were predicted well when a minimum amount of vertical prestressing was provided.