Abstract
Although many theoretical and experimental studies are available on external confinement of columns using fiber-reinforced polymer (FRP) jackets, as well as numerous models proposed for the axial stress-axial strain relation of concrete confined with FRP jackets, they have not been validated with a sufficient amount and variety of experimental data obtained through full-scale tests of reinforced concrete (RC) columns with different geometrical and mechanical characteristics. Particularly, no systematical experimental data have been presented on full-scale rectangular substandard RC columns subjected to reversed cyclic lateral loads along either their strong or weak axes. In this study, firstly, test results of five full-scale rectangular substandard RC columns with a cross-sectional aspect ratio of two (300 mm × 600 mm) are briefly summarized. The columns were tested under constant axial load and reversed cyclic lateral loads along their strong or weak axes before and after retrofitting with external FRP jackets. In the second stage, inelastic lateral force-displacement relationships of the columns are obtained analytically, making use of the plastic hinge assumption and different FRP confinement models available in the literature. Finally, the analytical findings are compared with the test results for both strong and weak directions of the columns. Comparisons showed that use of different models for the stress-strain relationship of FRP-confined concrete can yield significantly non-conservative or too conservative retrofit designs, particularly in terms of deformation capacity.
Highlights
A significant amount of the existing reinforced concrete (RC) buildings, in developing countries, has typical deficiencies, like low quality of concrete, poor details of reinforcement, use of plain bars, lack of adequate transverse reinforcement for shear effects and inadequate confinement reinforcement at the potential plastic hinging regions
Many studies have demonstrated the efficiency of fiber-reinforced polymer (FRP) for the repair and retrofit of typical RC members [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17], and numerous models have been proposed for the axial stress-axial strain relationship of FRP-confined concrete [18,19,20,21,22,23,24,25,26,27,28,29]
The specimens RET-35-N1, RET-35-N2 and RET-W-35-N2 were retrofitted were designed to fail in flexure and exhibit low ductility due to premature crushing of concrete and with external carbon fiber-reinforced polymer (CFRP) jackets with fibers aligned in the transverse direction
Summary
A significant amount of the existing RC buildings, in developing countries, has typical deficiencies, like low quality of concrete, poor details of reinforcement, use of plain bars, lack of adequate transverse reinforcement for shear effects and inadequate confinement reinforcement at the potential plastic hinging regions. The findings based on the comparison of experimental and analytical results in terms of lateral load-drift ratio relationships showed that the use of different available models could yield significantly different nonlinear behavior characteristics of retrofitted RC columns under lateral loads simulating seismic actions. This can cause remarkably non-conservative or too conservative estimation of the seismic performance of FRP-retrofitted RC columns.
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