Rectangular Concrete Column (ACI 318-14)
Run the calcDesign rectangular concrete columns to ACI 318-14 with customizable longitudinal bar layout. Checks include pure axial capacity, X- and Y-axis P-M interaction, biaxial bending via the Bresler method, and moment magnification for slender columns. Axial reactions from beams above link automatically.
This calculator uses an earlier code edition (ACI 318-14). It stays available for existing projects. For new designs, check the Calculator Library for the current edition.
Method & scope
Calculation method
The Rectangular Concrete Column (ACI 318-14) calculator designs columns in non-sway frames per ACI 318-14. LRFD load combinations determine the governing factored axial load Pu and biaxial moments Mu,x and Mu,y.Interaction diagram
The P-M interaction diagram is generated from the ACI rectangular stress block with ultimate concrete strain εcu = 0.003. At each point on the diagram, the neutral axis depth c is varied from zero (pure tension) to infinity (pure compression), and equilibrium between the concrete stress block and the reinforcement forces gives the corresponding Pn-Mn pair. The strength reduction factor φ transitions from 0.65 (compression-controlled, εt ≤ εy) to 0.90 (tension-controlled, εt ≥ 0.005) per ACI 318-14 Section 21.2. Failure mode (compression-controlled or tension-controlled) is reported for each axis check.Slenderness (non-sway frame)
For slender columns (klu/r > 22 for non-sway), design moments are amplified via the ACI moment magnification method: Mc = δs × Mu where δs = Cm / (1, Pu / 0.75Pc) Cm = 0.6 + 0.4 × (M1/M2) is derived from the user-entered end moment ratio. Pc is the Euler critical load based on the effective EI.Biaxial bending (Bresler method)
For combined biaxial bending and compression, the Bresler reciprocal load method is applied: 1/φPn,biaxial = 1/φPnx + 1/φPny, 1/φPo where φPnx and φPny are uniaxial capacities at the acting moment magnitudes about each axis, and φPo is the pure axial capacity. The biaxial utilization Pu / φPn,biaxial ≤ 1.0 must be satisfied for the column to pass.How to use it
1
Open the calculator
Open it from Run calc in the About this calculator panel above.
2
Enter your inputs
Work through the input sections from top to bottom. Click any input label to see its reference explanation, clause, conditions and assumptions. See Checks, References, Conditions and Assumptions.
3
Review the results and export
Check the utilization of each governing check in the summary, then export a PDF report. See Views and Export.
Common questions
What design method and standard does this calculator follow?
What design method and standard does this calculator follow?
Strength Design Method (LRFD) per ACI 318-14. LRFD load combinations from ASCE 7 determine the governing factored axial load Pu and biaxial moments Mu,x and Mu,y. ACI 318-14 Chapter 22 provisions govern the interaction diagram.
What are the key inputs?
What are the key inputs?
Column cross-section dimensions (h and b, in inches), concrete strength f’c (psi), lightweight concrete factor λ, column height L (ft), effective length factors K for X and Y axes, end moment ratio Cm, longitudinal bar size and count (corner bars plus optional additional top/bottom and left/right bars), reinforcement yield strength fy (40-80 ksi), clear cover to ties, optional default load eccentricities, and axial plus biaxial moment loads by load type.
How is biaxial bending handled?
How is biaxial bending handled?
The Bresler reciprocal load method is used: 1/φPn,biaxial = 1/φPnx + 1/φPny, 1/φPo, where φPnx and φPny are the uniaxial capacities at the acting moments about each axis and φPo is the pure axial capacity. The biaxial utilization Pu / φPn,biaxial ≤ 1.0 must be satisfied.
How does slenderness affect the design?
How does slenderness affect the design?
Slenderness is assessed using KL and radius of gyration r. For slender columns in non-sway frames (the assumed condition), moment magnification is applied via the Cm/δ method: design moments are amplified by the magnification factor δ = Cm / (1, Pu/0.75Pc). The ratio of end moments M1/M2 (entered as Cm) and bracing condition are user inputs.
Does the calculator check shear?
Does the calculator check shear?
Shear is flagged as a warning, it is not numerically checked. For columns carrying significant lateral loads, shear capacity should be verified separately per ACI 318-14 Chapter 22.
Does this calculator support load linking with beam calculations?
Does this calculator support load linking with beam calculations?
Yes, axial load reactions from connected beam calculations link directly to this column. When loads change in any upstream beam calculation, this column’s axial demand updates automatically.
Next steps
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