Research on Size Effect of Flexural Properties of High-Strength Reinforced Concrete Columns

It has been shown that as concrete strength increases, the size effect of ultimate flexural capacity becomes more pronounced in columns. However, the size effect of flexural capacity requires further confirmation for high-strength concrete columns. For this purpose, the high-strength concrete columns with a theoretical shear-span ratio of 4 were subjected to axial and monotonic loading in this study. The shear-span ratio, axial load ratio, and volume ratio of stirrup were consistent. The geometric similarity ratio of components was 3∶5∶7. The experimental results indicated that the failure mode of columns was flexural failure, and the splitting effect of concrete cover for large size columns might be a part reason of size effect. Meanwhile, the relative nominal flexural strength, nominal angle of rotation, P-Δ effect, and safety factors and local safety factors for flexural capacity decreased as section size increased, suggesting that size effect existed. Moreover, the size effect of relative nominal flexural strength and safety factors of flexural capacity was stronger for high-strength columns than for conventional concrete columns. In addition, based on the test results and Bažant’s Type 2 model, the calculation method of flexural capacity was modified to provide a constant factor of safety regardless of column size, indicating that the fluexural capacity was safer for large size columns.