Compressive behaviour of partially FRP confined concrete: Experimental observations and assessment of the stress-strain models

This study provides new insight on the compressive behaviour of partially fibre reinforced polymer (FRP) confined concrete with either strain-hardening or strain-softening responses. Fully FRP confined concrete, partially FRP confined concrete with different strip gaps, and unconfined concrete were tested under axial compression. Four types of axial load-axial deformation behaviours were observed for specimens with different strip gaps. Even though a high volumetric ratio of FRP was applied, the confinement effectiveness was negligible when the strip gap exceeded the diameter of the specimens. Moreover, the axial stress-axial strain behaviours of wrapped and non-wrapped concrete were observed to be different, and significant strain localization was observed within the non-wrapped region. Based on the experimental observations and an extensive literature review, a confinement effectiveness coefficient was proposed for partially FRP confined concrete. A stress-strain model was then developed by considering the proposed confinement effectiveness coefficient. The developed stress-strain model provided better predictions than other existing stress-strain models.