The influence of stirrup-confined action on the size effect of high-strength RC columns under small eccentric compression

Abstract

The aim of the present study is to explore the influence of stirrup-confined action on size effect of high-strength reinforced concrete (RC) columns subjected to small-eccentric ( e 0 =0.25 h 0 ) compressive loading. A series of eccentric compressive tests of the mechanical performances of 12 geometrically similar high-strength RC columns with different stirrups ratios (in the stirrup ratios of 0%, 0.66%) were conducted, in which the maximum cross-section size of the high-strength RC columns was 800 mm×800 mm. Moreover, a meso-scale simulation method for the investigation of the global mechanical properties of RC columns was established. The numerical tests on the RC columns with larger stirrup ratios (1.2% and 2.4%) was then carried out complementarily, based on the fact that the present simulation results were consistent with the available test observations. Subsequently, the failure behavior of the RC columns under eccentric loadings was studied, involving the failure patterns, the nominal compressive stress-strain relationships, the load-carrying capacity, the nominal compressive strength and the post-peak softening behavior. The size effect of nominal compressive strength was also explored. Furthermore, the influencing mechanism of stirrup-confined action on failure behavior and size effect of high-strength RC columns under small-eccentric compressive loading was revealed. One can conclude from the results that: 1) the size effect exists in the nominal compressive strengths of the eccentrically loaded high-strength RC columns with the present four different stirrup ratios; 2) the bi-logarithmic plots of nominal compressive strengths for RC columns under eccentric loading follows closely the “size effect law (SEL)” proposed by Bažant; 3) the presence of the stirrup confinement changes the failure patterns, improves the nominal strengths and makes the post-peak behavior of columns more ductile, and finally it weakens the corresponding size effect; 4) a meso-scale numerical method conducted presents the mechanical behavior of eccentrically loaded RC columns well.