Cyclic behaviour of concrete columns confined with FRP system

The subject of this paper concerns the problem of repairing and seismic retrofitting the existing reinforced concrete (RC) gravity load designed (GLD) buildings by using fiber reinforced polymers (FRPs). The paper presents several results from a wide experimental program in progress at the Laboratory of Structures of the University of Salerno (Italy). Full scale square (300x300 mm) RC columns were tested under a constant axial load and monotonic or cyclically reversed horizontal loads; in particular, two levels of the axial load were considered, while the horizontal action was applied under displacement control. Studied columns were designed to represent structural components of existing buildings, i.e. characterised by a concrete having low compression strength; for the same reason, tested columns were reinforced using both smooth and deformed steel rebars, while the reinforcement details (i.e. lap splice lengths, anchorages, hoop spaces, etc.) were arranged following design rules used in the past – nowadays not admitted in seismic zone – and without keeping into account any seismic details. Tests were conducted on FRP confined and unconfined RC columns: the confinement system was obtained by partially wrapping unidirectional carbon (CFRP) or glass (GFRP) layers around the RC member. Furthermore, a retrofitting system provided by both the external CFRP wrapping and steel angles has been considered, but tests performed on columns strengthened with this system are not discussed herein. Tests results have allowed to evaluate the benefits in terms of strength, ductility and energy dissipation capacity provided by FRP confining system.