RC Column - Axial & Bending
Rectangular section to AS3600:2018 + Amdt 2. Interaction diagram, check and design modes. Free, no login.
Preliminary tool, not certified engineering advice. Verify results against AS3600:2018 and obtain independent review before relying on any output. Certley accepts no liability for use of this calculator.
How it works
This calculator implements the rectangular stress-block method from AS3600:2018 Section 10 for reinforced concrete columns under combined axial load and bending. In Check mode you supply the section geometry, concrete grade, steel areas, and design actions N* and M*, and it returns the interaction diagram with the design capacity at the given axial load. In Design mode you enter N* and M*, and it calculates the required reinforcement ratio and total steel area for a symmetric two-face layout. Optional slenderness analysis (Cl 10.4/10.5) derives moment magnifiers and the capacity-reduction modifier. Optional biaxial bending check (Cl 10.6.4) evaluates the contour interaction.
What it calculates
The interaction diagram plots design capacity (φNu vs φMu) from squash load (Point A) through decompression (B), balanced point (C), pure bending (D), to pure tension (E). The stress-block factors α1, α2 and γ follow Cl 10.6.2. The capacity reduction factor φ transitions from 0.65 in compression to 0.85 in bending (Table 2.2.2).
The design point (N*, M*) is plotted against the diagram. If the point falls inside the capacity envelope the section is adequate. Design mode finds the minimum reinforcement ratio p by bisection. When slenderness is enabled, the calculator classifies the column as short or slender (Le/r limits per Cl 10.5.1), computes the buckling load Nc, moment magnifiers, and applies the magnified moment M*max to the capacity check. The capacity-reduction modifier is derived automatically (1.0 for short, 12/13 for slender). Biaxial bending evaluates the contour interaction of Cl 10.6.4.
Verify with a registered engineer
This tool produces preliminary results for concept design and cross-checking. Final designs must be verified and certified by a registered structural engineer. Need it certified? Get a quote from a Certley engineer.