Seismic performance of full-scale FRP confined substandard columns subjected to high axial load

Sub-standard columns are generally characterized with low quality of concrete, insufficient transverse reinforcement and improper detailing of reinforcements. These deficiencies lead to brittle behavior of columns during earthquakes, particularly in case of relatively high axial loads. In this study, full-scale reinforced concrete columns with a cross-sectional aspect ratio of two (300 mmx600 mm) are tested under constant axial load and reversed cyclic lateral loads before and after retrofitting with carbon fiber reinforced polymer composites. All specimens are subjected to high constant vertical load (approximately 35% of the axial load capacity of the columns) throughout the application of reversed cyclic lateral loads representative of seismic actions. One column is tested as the reference specimen, whereas others are tested after application of exterior FRP confinement to the potential plastic hinging zones. The amount of FRP used in retrofitting is intentionally designed below the requirements of the technical documents available in the world. However, test results indicate that full-scale sub-standard columns, retrofitted with less amount of FRP than requirements of the available design documents, can significantly benefit from external confinement with fiber reinforced polymer jacketing. Furthermore, test results are evaluated by using analytical approaches available in the literature and comparisons are made with the existing seismic assessment and design documents.