Numerical study of steel-to-FRP reinforcement ratio as a design-tool controlling the lateral response of SFRC beam-column joints

This study proposes both steel and fiber-reinforced polymer (FRP) composites as main reinforcement for modern reinforced concrete (RC) moment-resisting frame (MRF) structures. A detailed three-dimensional finite element model (3D FEM), which takes into account the material and geometric nonlinearity and the bond behavior of steel and glass FRP (GFRP) reinforcement, was created and validated against the available experimental results. 54 cases covering several combinations of steel-to-GFRP reinforcements and design scenarios (under and over reinforced design scenarios) were studied. The analysis results of steel-FRP reinforced concrete (SFRC) joints pointed to the ratio between the effective FRP reinforcement ratio and the balanced FRP reinforcement ratio (the normalized reinforcement ratio) as the main design tool that can be adopted to achieve a predefined seismic behavior. Moreover, a definition is given to the lower and upper limits of the normalized ratio. Design recommendations regarding the controllability of the serviceability state, the post-yielding state, the ultimate state, and the residual strength of SFRC joints through an appropriate design for the steel-to-FRP mixing ratio are drawn. Ultimately, a mechanical model describing the behavior of SFCR joints with different steel-to-FRP reinforcement ratios is introduced based on the general behaviors of the simulated joints.