Reinforced concrete columns of square and rectangular section, confined with FRP – Prediction of stress and strain at failure

Fiber-reinforced polymer (FRP) confined concrete columns under axial compression reveal significantly enhanced axial strength and ductility compared to unconfined columns. Adequate FRP confinement provide hardening stress – strain behavior up to failure especially in columns of circular section. However, it is difficult to model and predict accurately the maximum stress and ultimate strain of the noncircular confined concrete columns in the presence of internal steel reinforcement, which is the real case for the majority of existing structures. Numerous experimental investigations have been carried out for axially loaded circular section concrete columns with or without internal steel reinforcement confined with FRP materials and other techniques. Also, a lot of predictive expressions of peak axial strength and strain and ultimate stress and strain, suitable for similar concrete sections, have been proposed. On the other hand, fewer studies concern reinforced concrete columns of square and rectangular section. The presented investigation gathers all the newest available test results on square and rectangular reinforced or plain concrete columns confined with composite reinforcements and assesses the performance of significant predictive expressions published in literature. The developed database includes these columns confined with FRP materials and other techniques and assesses the performance of 24 existing models proposed for the peak and ultimate conditions.