Experimental and analytical study on properties affecting the behaviour of FRP-confined concrete

Abstract

The use of fibre reinforced polymer (FRP) composites has been successfully promoted and experienced for external confinement of reinforced concrete (RC) columns and pillars all over the world. Increase in compressive strength and energy absorption before collapse have been largely experienced in laboratory environment during the last decade, mostly by testing concrete cylinders wrapped with FRP jackets.In this study the results of a large test program are presented with the objective of examining the effect of various experimental parameters on the confinement effectiveness of FRP jackets on both circular and rectangular concrete columns with solid or hollow core. The experimental parameters include: different concrete strength, type of fibres, number of wrap layers, geometry of the column, corners radius, full/hollow core and cross-sectional aspect ratio (only for prismatic elements). FRP-confined and unconfined specimens have been loaded in uniaxial compression until failure. Totally 128 specimens were prepared and tested, 89 of them were strengthened with Carbon FRP (CFRP) and Glass FRP (GFRP), the remaining 39 were tested as plain concrete reference. Compressive stress, axial and hoop strains have been measured to evaluate the stress–strain relationships, ultimate strength, stiffness, and ductility of the specimens. Results confirmed that external confinement produced by FRP can significantly enhance compressive strength, ductility and energy absorption capacity if compared to those of plain concrete. The effects of test parameters are evidenced and compared in order to show the sensitiveness of the mechanical problem for each of them. Important design information are furnished to researchers and practitioners also by comparing the results of the experimental campaign with the prediction of different analytical models, based on well-known and widely accepted mechanical assumptions. Design equation recommended by CNR (Italian National Research Council) were also applied by assuming unitary values for safety factors, in order to see the reliability of the mechanical model proposed by CNR.