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An accurate estimation of the effective ultimate strain of the FRP jacket is crucial to determine the values of strength and ultimate strain of FRP confined concrete. However, this is one of the main aspects not yet resolved by the theoretical models. Published design recommendations differ on this aspect, particularly in the case of non-circular sections. In this work, an experimental program carried out on 38 square section concrete specimens confined with FRP is presented. The results show a great influence of the radius of rounding of the corners on the behaviour of FRP confined square columns. The experimental values of effective ultimate strain are compared with the recommended values given by design guidelines.

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A significant amount of research has been conducted on FRP-confined circular columns, but much less is known about rectangular/square columns in which the effectiveness of confinement is much reduced.This paper presents the results of experimental investigations on low strength square concrete columns confined with FRP. Axial compression tests were performed on ten intermediate size columns. The tests results indicate that FRP composites can significantly improve the bearing capacity and ductility of square section reinforced concrete columns with rounded corners. The strength enhancement ratio is greater the lower the concrete strength and also increases with the stiffness of the jacket.The confined concrete behaviour was predicted according to the more accepted theoretical models and compared with experimental results. There are two key parameters which critically influence the fitting of the models: the strain efficiency factor and the effect of confinement in non-circular sections. RESUMEN:Comportamiento de hormigón confinado con FRP en pilares cuadrados. La mayoría de las investigaciones sobre hormigón confinado con FRP se han realizado sobre pilares de sección circular, pero el comportamiento en secciones cuadradas/rectangulares, donde el confinamiento es menos eficaz, es mucho menos conocido.Este trabajo presenta los resultados de un estudio experimental sobre probetas de hormigón de baja resistencia y sección cuadrada. Se han ensayado a compresión centrada diez probetas de tamaño intermedio. Los resultados indican que el confinamiento mejora significativamente la resistencia y ductilidad del hormigón en columnas de sección cuadrada con las esquinas redondeadas. El incremento de resistencia es mayor cuanto menor es la resistencia del hormigón sin confinar y también aumenta con la rigidez del encamisado.Los resultados se compararon con los obtenidos según los modelos teóricos más aceptados. Hay dos pará-metros críticos en el ajuste de los modelos: el factor de eficiencia de la deformación y el efecto de confinamiento en secciones no circulares.