Cyclic behavior of reinforced rubberized concrete columns under flexure-shear interaction

Abstract

The influence of rubber aggregate stiffness on the cyclic performance of concrete columns exhibiting flexure-shear interaction remains unclear. It is also uncertain whether existing design provisions can be applied effectively to rubberized concrete columns with these properties. This study examines the cyclic behavior of six circular columns designed for flexure-shear interaction at two ductility levels: limited (LD, $\mu \le 2$) and moderate (MD, $2<\mu \le 4$). The 500 mm diameter columns had an aspect ratio of 2.5 and a constant axial load ratio of $0.10{\text{f}}_{\text{c}}^{\prime }{\text{A}}_{\text{g}}$. Columns with rubber contents by total aggregate volume of 10 % (R10), and 20 % (R20) were tested, along with a conventional concrete mix (CM2) of comparable compressive strength to R10 mix. R10 columns exhibited minor delays in concrete crushing and rebar buckling, with ductility increases of 10 % (LD) and 3 % (MD) and shear strength variations of less than 1 % compared to CM2. However, increasing rubber content to 20 % led to performance declines, with R20 columns showing shear strength reductions of 21 % (LD) and 14 % (MD) relative to their R10 counterparts. Assessment of design provisions for circular columns indicated that, for rubber contents up to 20 % and axial load ratios up to 10 %, shear strength and stiffness of rubberized concrete columns can be conservatively predicted by solely accounting for the change in compressive strength.