Compressive behavior of concrete filled steel tubular columns subjected to long-term loading

Despite many successes in concrete creep studies, its effect on the mechanical behavior of concrete members is far from a thorough understanding. For the members subjected to a long-term loading, the classical stress–strain models for the short-term behavior of confined or uniaxially loaded concrete are not suitable. An experiment procedure was designed to investigate the effect of long-term loading on the compressive strength, modulus of elasticity, and stress strain of confined concrete. Eight concrete filled steel tubular (CFT) columns were prepared, four of which were subjected to constant compressive loadings for 411 days then unloaded, and the other four were companion load-free specimens. After two weeks of creep recovery, the specimens were axially loaded in compression up to failure. Based on the microprestress solidification theory for concrete creep and a plasticity model for concrete, an analytical model was presented to predict the behavior of CFT columns after creep. The comparison between the model predictions and the experimental results shows a good agreement. Both the experimental and theoretical results indicate that after creep the elastic modulus of CFT columns increased, while the compressive strength slightly decreases.