Experimental evaluation of short reinforced concrete columns under varying mix ratios and shape configurations

Abstract The present study examined the compressive behavior of short reinforced concrete columns with varying cross-sectional geometries with three mix ratios (1:2:4, 1:1.5:3, and 1:1:2) while maintaining identical reinforcement detailing. The investigation focused on the load-displacement response, stiffness variation, and failure characteristics under axial loading. The dominant mode of failure of the columns is compression crushing and spalling of concrete. Specimens with the 1:1:2 mix exhibited the highest failure load capacity, exceeding that of 1:1.5:3 and 1:2:4 mixes, with a record of 54% increase in failure load in square shape column. The 1:1.5:3 mix demonstrated moderate strength with higher stiffness, whereas the 1:2:4 mix showed lower strength but enhanced deformability. In contrast, geometric variation exhibited a dominant influence on stress distribution and confinement. Square and L-shaped columns exhibited superior performance in stiffness and ductility, with 46% higher stiffness over the L-shaped column, combining higher load resistance and energy absorption, whereas circular sections exhibited brittle failure. The results suggest that cross-sectional geometry plays a critical role in determining confinement efficiency and failure mode, often offsetting the marginal gains from richer mix compositions. Overall, the study underscores the interdependence between material composition and geometric configuration in governing the nonlinear compressive response of short reinforced concrete columns, providing valuable insights for optimizing mix design and column geometry in structural applications.