Factored axial capacity of a short braced RC column per IS 456:2000 Cl 39.3 — with the Cl 25.4 minimum-eccentricity and slenderness gates that decide whether the shortcut applies at all.
0 if unknown
Factored axial capacity
kN
Service load kN (Pu / 1.5)
IS 456:2000 Cl 39.3 (Reaffirmed 2021): Pu = 0.4·fck·Ac + 0.67·fy·Asc, with Ac = gross area minus steel. Two gates guard the shortcut: the load eccentricity must sit within the Cl 25.4 minimum, max(l/500 + D/30, 20 mm), and the column must be short (effective length over least dimension ≤ 12). Steel must stay between 0.8% and 6% of gross per Cl 26.5.3.1.
When a gate fails, the calculator prints the reason instead of a number: eccentric columns need Cl 39.4/39.5 combined bending design, slender ones Cl 39.7 additional moments. A number you can’t trust is worse than no number — and concrete is unforgiving of guessed columns.
Given: 300 × 300 mm column, M25, Fe500, 6–16 mm bars, 3.0 m effective length, concentric load.
Gates: eₘₐₗ = max(3000/500 + 300/30, 20) = 20 mm ≥ e ✓; slenderness 3000/300 = 10 ≤ 12 ✓; steel 1206/90,000 = 1.34% (0.8–6% ✓)
Pu = 0.4×25×88,794 + 0.67×500×1206 = 888 + 404 = 1292 kN
Service load = 1292/1.5 = 861 kN — for the concentric ideal; frame moments reduce what the same column safely carries.
Those are the coefficients of IS 456 Cl 39.3 itself for axially loaded short columns: they fold in the material partial safety factors plus the fact that a tied column’s steel cannot reach its full design stress at the concrete’s ultimate strain. Use them exactly as published — do not rebuild them from the flexural values.
Two gates. First, eccentricity must stay within the Cl 25.4 minimum — max(l/500 + D/30, 20 mm); anything more eccentric needs the combined axial + bending design of Cl 39.4/39.5. Second, the column must be short: effective length over least lateral dimension ≤ 12. Slender columns carry additional moments per Cl 39.7 and buckle below this capacity. This calculator refuses to print a number when either gate fails.
Below about 0.8% a column behaves closer to plain concrete — a sudden brittle failure with almost no warning; the minimum steel keeps some ductility and controls thermal and creep strains. Above 6%, congestion prevents proper compaction around bars, so IS 456 Cl 26.5.3.1 caps it — with 4% the practical ceiling where bars are lapped.
The calculator reports the factored capacity Pu and the service load Pu/1.5 — the safe long-term working load for a perfectly concentric, braced, short column. Real columns carry moments from frame action and imperfection; the design engineer must confirm the whole load path, not just this axial number.
Often used together with this calculator — pick the next step in your design or QA loop.
Deep dive: read the full significance guide — the code clauses, assumptions and site meaning behind these numbers.
Often used together with this calculator — pick the next step in your design or QA loop.