Axial performance, stiffness, and failure modes of circularly tapered non-prismatic reinforced concrete columns

Most structural codes focus on prismatic columns, often overlooking the benefits of non-prismatic shapes. This study investigates how reinforced concrete columns tapered along a circular arc behave compared to standard prismatic ones under axial loads. Four specimens were tested (2 prismatic and 2 non-prismatic). Using 1.5m height specimens with equal reinforcement (6φ10) and a constant depth of 150mm, the experimental program tested columns that varied their width from 300mm at the ends to 150mm at mid-height as non-prismatic columns, whereas the prismatic columns had a section of 150mm x 150mm. Results revealed that non-prismatic columns have a higher load carrying capacity than prismatic columns by 17.90% and improved axial stiffness by at least 74.03%. Notably, while prismatic columns failed in the upper half, tapered specimens failed at the necking region, demonstrating a more efficient use of the entire member. Additionally, the strain in the curved rebars was 66% of that recorded in prismatic members at equivalent load level. Although non-prismatic columns dissipate less energy than prismatic specimens (1306.71J compared to 2137.33J) and exhibited a more brittle response, they maintained superior lateral stability. Within the limits of the tested specimens, this study supports that the circularly tapered shape increases strength due to improved confinement provided by bi-axial compressive stress within the column, thereby offering a more efficient method for structural design.