Energy-based structural performance of rock-filled concrete columns under eccentric loading

The study presents an experimental–numerical study of rock-filled concrete (RFC) columns incorporating variable rock sizes and volumetric contents under eccentric compression loading. The matrix was made of self-compacting concrete (SCC) of grade C30, and rectangular precast columns (300, 250, 1200 mm) were manufactured, having rock inclusions fitted in low-stress zones. Three rock volumetric fractions (35, 45, and 55%) and three rock size ranges (A: 6.25–9.375 cm, B: 9.375–12.5 cm, and C: 12.5–18.75 cm) were investigated, along with a control specimen. Eccentric compression tests were conducted under displacement control. A validated Abaqus/Explicit finite-element model employing the concrete damaged plasticity (CDP) framework and cohesive interfacial transition zone (ITZ) formulation achieved 96.83% agreement with experimental peak loads. Results indicate monotonic reductions in ultimate load capacity of 39.35%, 45.12%, and 51.37% at rock contents of 35%, 45%, and 55%, respectively, while first-cracking loads decreased by 19.25%, 26.51%, and 42.68%. Rock sizes not exceeding 12.5 cm presented the most stable structural performance, whereas larger sizes (group C) were coupled with intensified crack localization and earlier brittle failure. Analysis of energy characterized ductile specimens (control, A-series, and B-1 and B-2), with stabilized ETOTAL and insignificant ALLVD, while brittle specimens (B-3, C-2, and C-3) exhibited pronounced ETOTAL degradation with sharp ALLVD growth. The results confirm that safe RFC column performance requires optimizing both rock size and volumetric content to avoid ductility loss and premature brittle failure.