Nonlinear Finite Element Modelling and Parametric Analysis of Shear Strengthening RC T-Beams with NSM CFRP Technique

Abstract

In this study, a robust three-dimensional finite element (FE) model has been developed for reinforced concrete beams strengthened in shear with near surface mounted (NSM) carbon fibre reinforced polymer (CFRP) rods. The FE models were developed and validated against existing experiments and presented various nonlinear constitutive material laws and interfacial relations. A detailed parametric study was performed to investigate the effects of various parameters on the performance of strengthened member. It was shown that increasing the concrete compressive strength ( $${f_{\text{c}}}^{\prime }$$ ) from 20 to 50 MPa, leads to an increase in the beam’s ultimate load and contribution of NSM CFRP reinforcement. While for NSM reinforcement ratio ( $${\rho _{\text{f}}}$$ ), the ultimate load slightly increased when $${\rho _{\text{f}}}$$ is 0.14–0.22%, and then increased by 11% in average when $${\rho _{\text{f}}}$$ increased to 0.28%. Varying the percentage of existing steel stirrups ( $${\rho _{{\text{sw}}}}$$ ) from 0.11 to 0.36%, leads to an increase in ultimate load from 8 to 15% compared to the control un-strengthened specimen. However, the further increase in $${\rho _{{\text{sw}}}}$$ (more than 0.36%) caused a reduction in the contribution of NSM CFRP technique because of the changing in the failure mode. The distance between existing steel stirrups and NSM reinforcement does not affect the behaviour. In addition, the model predictions were used to evaluate several design formulas available in the literature for this technique. It was found that some theoretical equations were conservative as long as the governing failure mode is shear.