Evaluation of stress–strain models for FRP confinement of rectangular RC columns based on structural reliability and design guidelines

Resumo

The global demand for sustainable practices in the built environment requires the management of the life cycle of existing structures. In this context, the service life of a structure is not determined only by its current condition. Among the various techniques employed for the repair and strengthening of existing structures, the use of Fiber Reinforced Polymer (FRP) composites as confinement elements in Reinforced Concrete (RC) columns has proven to be a viable and competitive alternative. However, research and practical applications have mainly focused on cases in which the confinement mechanism is easily understandable and quantifiable, particularly in RC columns under axial load and with circular cross-sections. Nonetheless, in practical applications, there is a clear need to address additional cross-sectional geometries, such as square or rectangular sections. In such cases, the effectiveness of confinement depends significantly on geometric aspects, such as corner radius, and on the interaction between the RC and the FRP jacketing.Over recent decades, several stress–strain models have been proposed for FRP-confined concrete elements, based on different premises and objectives (including empirical, semi-empirical, and analytical approaches). These models serve distinct functions, such as direct application in design, structural assessment, or implementation in computational tools. This paper presents a critical evaluation of models for square and rectangular RC columns confined with FRP, with particular attention to parameters such as cross-section, concrete strength, loading condition (concentric and eccentric), FRP jacket stiffness, fiber orientation, lateral expansion, longitudinal and transverse reinforcement ratios. Both normative models and relevant proposals from technical literature are addressed and discussed based on their methodological structure and functional purpose.The differences between the models in the representation of confinement mechanisms are addressed, with attention on corner radius and the interaction between FRP and transverse reinforcement acting simultaneously. The analysis of the models consolidates a technical and theoretical basis for representing FRP confinement in square and rectangular columns, highlighting relevant aspects for structural reliability assessments.