Behavior of axially and eccentrically loaded square RC columns retrofitted with steel strips

Abstract

This paper introduces experimental and theoretical research on the compression behavior of reinforced concrete (RC) columns after retrofitting. The axially loaded columns were retrofitted by steel strips, while the eccentrically loaded columns were retrofitted by steel strips and steel plates. The main parameters of the fourteen RC columns are eccentricities, spacing and layers of steel strips. Three failure modes were observed and controlled by the eccentricity. Reducing the spacing of the steel strips increased the capacity by 24 %− 30 % for retrofitted axial columns, which revealed that the confinement effect was significantly improved with the enlarged confined region of the steel strips. The RC columns retrofitted with single-layer steel strips improved the capacity by 24%− 36%, the displacement by 12 %− 210 % and the ductility by 19 %− 345 % compared with the unretrofitted columns under various eccentricities. However, double-layer steel strips improved the 1 %− 16 % capacity compared with single-layer steel strips, while the displacement enhanced 22 %− 83 % due to the lag effect of the outer-layer steel strips. To predict the behavior of retrofitted eccentric RC columns, a modified constitutive model of eccentric concrete based on the behavior of axial concrete was adopted. The capacity, bending moment and deflection of eccentric columns can be deduced by an iterative procedure. The proposed model was verified to safely predict the behavior of retrofitted RC columns by the N-M interaction curve.