K-Factor Check
Effective Length Factor Calculator
Use this page to compare common end-restraint assumptions, convert unsupported length into effective length, and see how K changes elastic column capacity.
Enter length in meters, E in GPa, inertia in cm^4, area in cm^2, and applied axial load in kN.
Buckling Inputs
End condition
Member data
Use the end condition that best matches the expected rotational restraint.
Use the weaker-axis inertia when buckling can occur about multiple axes.
Area is used to calculate the radius of gyration and slenderness.
Applied load is compared directly with the ideal Euler critical load.
Buckling Diagram
Stability Summary
| End condition | Fixed-Pinned |
| Effective length factor K | 0.699 |
| Radius of gyration r | 7.64 cm |
| Euler stress Fe | 989.79 MPa |
| Load margin Pcr - P | 3,857.10 kN |
Buckling Formula
Effective length
General form
L_e = K L
With current values
L_e = 0.699 * 5.00
Calculated result
L_e = 3.49 m
Euler critical load
General form
P_cr = pi^2 E I / L_e^2
With current values
P_cr = pi^2 * 210 * 2,450 / 3.49^2
Calculated result
P_cr = 4,157.10 kN
Slenderness ratio
General form
lambda = L_e / r, r = sqrt(I / A)
With current values
lambda = 3.49 / sqrt(2,450 / 42)
Calculated result
lambda = 45.76
This screen applies classical Euler elastic buckling and is most reliable for slender columns before inelastic or code-specific checks.
Model Assumptions
- The column is straight, prismatic, and loaded concentrically.
- Material behavior is linear elastic up to the predicted buckling load.
- Only ideal Euler global buckling is screened here; local buckling and imperfections are excluded.
Engineering Reading
Calculation Basis
Assumptions & Limits
- The model screens ideal global Euler buckling only and does not include local buckling or material nonlinearity.
- Imperfections, eccentricity, and frame sway effects need separate engineering review.
- K-factors are modeling assumptions about end restraint and should be treated as a sensitivity study when restraint is uncertain.
Reference Basis
- Documentation: Methodology
- Documentation: Engineering Review
- Roark's Formulas for Stress and Strain
- Mechanics of Materials references
- Euler buckling and column-stability references
K-Factor Reference Cases
| Pinned-pinned | K = 1.00 |
| Fixed-fixed | K = 0.50 |
| Fixed-pinned | K = 0.699 |
| Cantilever | K = 2.00 |
| Main use | Translate support restraint into effective length |
Engineering Notes
- Use this page when the biggest uncertainty is not the steel section itself, but how much rotational restraint the framing really provides.
- Because Euler load scales with 1 over Le squared, small changes in K can move the predicted elastic buckling load much more than many users expect.
- If frame action, sway, or connection flexibility are uncertain, use this page as a sensitivity study rather than picking one K value and treating it as absolute.
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