Buckling resistance of layered reinforced concrete columns: Experimental evaluation of normal and lightweight thermo-stone aggregate configurations

Reinforced concrete (RC) columns are the vital part of building structures and play an important role in the stability and safety of the entire building under axial compression load. In this study, the buckling performance of layered RC columns made of NC, LWC and containing thermo-stone aggregate replacements was studied experimentally. Eighteen square and circular RC columns with different layer arrangements—LNN, LNL, and NNL—were tested under axial loading. Results showed that the NNL and LNN geometry performed better than the fully LWC columns in terms of axial compression and buckling. More precisely, square NNL columns with 25% thermo-stone replacement can attain an axial load capacity of 339.13kN, that represents a value 21.6% larger than the same fully LWC column (278.85kN). Similarly, layered circular columns with 50% thermo-stone replacement (CR-7 and CR-8) recorded 290.5–290.8kN, compared to 245.9kN for the fully LWC counterpart (CR-6). Deflections ranged from 3.75 mm in NC columns to 5.23 mm in layered LWC columns. Square columns consistently exhibited higher buckling resistance than circular ones due to their greater moment of inertia. The findings highlight that strategically placing NC in the middle and upper layers enhances structural performance while maintaining weight reduction.