Non-linear modeling of RC rectangular hollow piers confined with CFRP

Hollow bridge Reinforced Concrete (RC) piers withstand high moment and shear demands by reducing the self-weight and the high bearing demand on foundations, maximizing structural efficiency of the strength–mass and stiffness–mass ratios and reducing the mass contribution of the column to seismic response where high seismic actions and natural boundaries require high elevation infrastructures. Column jacketing with Fiber Reinforced Polymer (FRP) composite materials has been extensively investigated in the last decade and researchers have mainly focused their attentions on solid columns. Few researches can be found on hollow columns strengthened with FRP. The proposed confinement model, coupled with the proposed computation algorithm, is able to predict the fundamentals of the behavior of hollowrectangular members confined with FRP both in terms of strength and ductility tracing the occurrence of the brittle mechanisms, namely concrete cover spalling and reinforcement buckling (a common failure mode of hollow members), and the evolution of stress and strains in the concrete and in the confinement jacket, allowing evaluation at each load step the multiaxial state of stress and eventually the failure of concrete or of external FRP reinforcement. The main output of the proposed model is also the assessment of the member deformability in terms of both curvature and displacement ductility. Results of theoretical analyses and experimental tests (performed by the authors) show that a good agreement was achieved.