Size effect tests of high-strength RC columns under eccentric loading

The objectives of the study are to examine the possibility of existence of size effect in eccentrically loaded high-strength reinforced concrete (RC) columns, and discover the confinement effect of transversal reinforcement on the size effect. A series of eccentric compressive tests of 24 geometrically similar high-strength RC columns with different structural sizes (with ratio 1:2:4, and slenderness of 4.5), different eccentricities and different stirrups ratios were conducted. Two eccentricities (i.e., 0.6h0 and 0.25h0, for large and small-eccentric loadings respectively) and two groups of columns with and without stirrups at the mid-length were utilized. The widths of the square cross-section of the RC columns tested were between 200 mm and 800 mm, and the lengths varied from 900 mm to 3600 mm. The behavior of the RC columns, involving the failure patterns, the nominal compressive stress-strain relationships, the ductility, the nominal strength and the post-peak behavior of columns were observed and explored. The test results demonstrate the existence of size effect in both the large and small eccentrically-loaded RC columns. The presence of the transverse reinforcement changes the failure patterns, improves the nominal strengths and makes the post-peak behavior of columns less brittle. Compared to the columns with middle stirrups, the ones without stirrups at the mid-length present a stronger size effect for their higher brittleness. Moreover, the tested nominal strengths follow closely the “size effect law (SEL)” proposed by Bažant.