Mechanical behavior and size effect of moderate high-strength RC columns under monotonic and cyclic axial compression

• Size effect tests of 16 high-strength RC columns under axial compression are reported.
• The cross-sectional size of the RC columns ranges from 200 mm to 800 mm.
• Test results confirm the existence of size effect in relatively larger-sized RC columns.
• The nominal strength of RC columns follows closely the size effect law proposed by Bažant.

The reliable design of reinforced concrete (RC) structures against external mechanical forces, including earthquake-induced, impact and other types of forces, necessitates a clear understanding of the mechanical behavior and size effect of moderate high-strength RC structural members under cyclic loading. This study presents the results of an experimental study on a series of geometrically similar moderate high-strength RC columns under monotonic and cyclic axial compression. A total of 16 moderate high-strength RC columns with different structural dimensions (in the ratio 1:2:3:4) were tested. The cross-sectional size of the columns was between 200 mm and 800 mm, and the length varied from 600 mm to 2400 mm. The overall mechanical performances of the moderate high-strength RC columns, including the failure patterns, the hysteretic curves, the nominal compressive stress-strain relationships, the peak load-carrying capacity, the energy-dissipation capacity, the nominal compressive strength, the concrete softening behavior and the buckling/necking of steel rebar were observed and explored. The test observations indicate the existence of size effect in relatively larger-sized moderate high-strength RC columns under both monotonic and cyclic axial compression, and the RC columns under cyclic loading pronounce a more obvious size effect. It is found that the bi-logarithmic plots of nominal compressive strengths for different moderate high-strength RC columns follows closely the “size effect law (SEL)” proposed by Bažant.