Mechanical performances of concrete beams with hybrid usage of steel and frp reinforcement

Abstract

Fiber-reinforced polymer (FRP) bars have been recently employed to reinforce concrete members due to their high tensile strength and especially in corrosive environments to improve the durability of concrete structures. However, FRP composites have a low modulus of elasticity and a linear elastic behavior up to rupture, thus reinforced concrete (RC) components with such materials would express a lack of ductility. In order to increase the mechanical performances of RC beams, the hybrid usage (also called combined usage) of FRP and steel reinforcements in shear and flexure is proposed.

At first, an experimental investigation of concrete beams strengthened in shear by FRP bars using embedded through-section (ETS) technique is carried out to study the efficiency of the strengthening system under various effects. The prediction of shear contribution of the retrofitting system is also proposed. Additionally, the pullout tests are conducted to investigate the bond response between ETS bars and concrete under various influences. Furthermore, the finite element (FE) simulation of the tested beams to validate the effectiveness of the FE tool is offered. Comparison between the results attained from this study and the literature displays the significant improvement in the shear efficiency of the ETS strengthening system with the anchorage installation. Furthermore, for the concrete beams strengthened in shear using ETS method, the truss analogy theory with the developed average strain formulation is an effective method to predict the shear resisting force of the anchored ETS FRP bars.

In the second part of research, this study presents a numerical and analytical study on the structural behaviors of concrete beams with the combined usage of FRP and steel tension reinforcement employing three-dimensional (3D) FE modelling. The ductility of the hybrid FRP-steel RC beams under important effects is closely analyzed through parametric study. Based on the investigated results, the conditions of the ratio of FRP to steel reinforcement, the location of the FRP reinforcement and the type of FRP reinforcement required to obtain reasonable ductility in practical use are presented.