Concrete Column Load Capacity Calculator
Estimate the maximum axial load for reinforced concrete columns (Short vs Slender) using ACI 318 formulas. Checks for buckling risks.
1. Column Properties
2. Reinforcement
About
Columns are the most critical structural elements; their failure is often catastrophic. This calculator estimates the nominal axial load capacity (Pn) of a tied rectangular reinforced concrete column. It accounts for the contributions of both the concrete core and the longitudinal steel bars.
The tool distinguishes between "Short" columns (governed by material strength) and "Slender" columns (governed by buckling instability). By inputting the effective length factor (K) and unbraced length (Lu), engineers can assess if slenderness effects reduce the column's capacity. Standard strength reduction factors (φ = 0.65 for tied columns) are applied to provide the Design Axial Strength (φPn).
Formulas
The maximum nominal axial load (P0) for a short column is the sum of concrete strength and steel strength:
However, accidental eccentricity limits the maximum design load (Pn,max) to 80% of P0 for tied columns:
The Design Capacity incorporates the safety factor φ:
Reference Data
| Condition | Factor (K) | Description |
|---|---|---|
| Pinned-Pinned | 1.0 | Both ends hinged; free to rotate. |
| Fixed-Fixed | 0.5 | Both ends rigid; no rotation. |
| Fixed-Pinned | 0.7 | One end rigid, one end hinged. |
| Fixed-Free | 2.0 | Flagpole (cantilever); very unstable. |
| Tied Column φ | 0.65 | Strength reduction for tied reinforcement. |
| Spiral Column φ | 0.75 | Strength reduction for spiral reinforcement. |