Investigation of Bar Buckling in Columns Confined with Composite Material Jackets

The onset and evolution of bar buckling at the plastic hinge of old-type reinforced concrete (RC) columns confined with composite material [textile-reinforced mortar (TRM) and fiber-reinforced polymer (FRP)] jackets was investigated experimentally and analytically in this study. The interaction between composite jacket (or concrete cover, for unconfined concrete) and embedded longitudinal compression reinforcement at the onset and evolution of bar buckling was achieved through strain measurements of the compression reinforcement. Moreover, the implementation of a stress-strain confinement model, which relates lateral with axial strains, allowed the description and monitoring of the axial-lateral strain relationship at the base of the columns throughout the evolution of bar buckling. Finally, based on the aforementioned confinement model and on the experimental measurements, the post-buckling behaviour of columns was related with the stiffness of the jacket.JRC.G.5-European laboratory for structural assessmen