Performance-Based Seismic Design of Hybrid GFRP-Steel Reinforced Concrete Bridge Columns

Damage quantification in terms of engineering demand parameters (EDPs) is a critical element of the performance-based design (PBD) approach. A widely used EDP for reinforced-concrete (RC) bridge columns is the drift ratio. This study establishes drift ratio limit states, and corresponding strengths for hybrid GFRP-steel RC circular bridge columns. The adopted reinforcement layout in this study consists of two layers of reinforcement, exterior with GFRP and interior with steel. Such coupling between the two materials in concrete bridge columns improves their corrosion resistance while maintaining their stiffness and ductility. Here, a validated fiber-based model is utilized to predict global as well as local responses of hybrid RC columns under monotonic displacement-controlled loading. A full factorial analysis was first adopted to screen parameters potentially influencing drift ratio limit states and corresponding strengths for their significance. The resulting data were then fitted to mathematical expressions using machine learning-based symbolic regression. Lateral load-deformation responses predicted based on the proposed expressions were validated against existing data from the literature. A complete example demonstrating how the proposed expressions could be utilized to design a hybrid bridge column within the context of PBD is also presented.