Home / Services / Steel structure design (structural and detail drawings) / Steel Column Check Calculator: Buckling Under Axial Compression to DBN
Steel structure design (structural and detail drawings)
Steel Column Check Calculator: Buckling Under Axial Compression to DBN
The calculator checks a centrally compressed solid-section steel column to DBN V.2.6-198:2014: effective length, slenderness about both axes, the buckling coefficient φ, the buckling and strength checks, and the limiting slenderness. The section can be taken from our sortament (I-beams, channels, tubes) or entered by hand. The result is an estimate: the final check is made by the project designer.
Contents
Column check calculator
Choose the section type and size, the steel grade and the plate thickness, then enter the column length, the end restraint and the axial force N. The result updates at once and no data is sent anywhere.
This is an estimate. The final calculation is made by the project designer to the codes in force; the consequence class, loads and restraints for the project are set by the designer.
Send a drawing or a sketchExample: I-beam No. 30, 4 m column
Take the conditions from the article on steel column design: I-beam No. 30, steel S255, flange thickness over 10 up to 20 mm (Ry = 240 N/mm²), length 4 m, pinned at both ends (μ = 1.0), N = 600 kN, γn = 1.05, γc = 1.0.
Without out-of-plane bracing the column fails: the governing axis is y–y, φ = 0.295, and buckling is used at 191 %. If you enter 2 m in the “Length between restraints” field (bracing or wall girts at mid-height), φ rises to 0.734 and the utilisation falls to 77 %. Strength in this example is used at 56 %, the limiting slenderness is λu = 136 and the greatest slenderness is 74.3.
| Case | Governing axis | φ | Buckling utilisation | Result |
|---|---|---|---|---|
| No bracing | y–y, lef = 4000 mm | 0.295 | 191 % | fails |
| Bracing at mid-height | y–y, lef = 2000 mm | 0.734 | 77 % | passes |
| Either case | x–x, lef = 4000 mm | 0.936 | 60 % | passes |
What exactly the calculator does
The sequence is the same as in the article, and each step carries its DBN clause number:
- effective length lef = μ·l (cl. 13.3.1), separately for the x–x and y–y axes;
- slenderness λ = lef / i and relative slenderness λ̄ = λ·√(Ry / E), with E = 2.06·10⁵ N/mm²;
- coefficient φ from formulas (8.4) and (8.5) with buckling curve a, b or c (Table 8.1): at λ̄ < 0.4 φ = 1 is taken, and at high slenderness φ cannot exceed 7.6 / λ̄²;
- the buckling check by formula (8.3) with the smaller of the two φ values, and the strength check by formula (8.1);
- limiting slenderness from Table 13.9, item 4 (main columns): λu = 180 − 60α, with no 10 % increase under cl. 13.4.2.
The calculator sets the buckling curve from the section type: b for an I-beam, c for a channel, a for tubes. For a custom section you choose the curve. The design strength Ry comes from Table G.2 for grades S245, S255 and S345 by the greatest thickness of a section element; for tubes, roll-formed sections and a custom section it is the value for plate. If the steel is different, enter Ry by hand.
What the calculator does not check
- local stability of webs and flanges (cl. 8.3): requirements 8.3.2–8.3.8 are met separately;
- flexural-torsional buckling of open sections without battens or lacing (cl. 8.1.5);
- eccentric compression, that is a column carrying a bending moment (Section 10 of DBN);
- stepped columns, elastic end restraint and frame columns, for which μ comes from other clauses and tables;
- equal-leg angles: the sortament table gives their properties about axes parallel to the legs, while a column needs the principal axes, so such a section is entered as a custom one;
- joints, the column base and the foundation.
So a “passes” answer only means that these separate checks are met. The full calculation to the codes in force is made by the project designer.
Codes and their validity
The formulas and the order of the check come from the article on steel column design. The sources are DBN V.2.6-198:2014 (in force; edition with Amendment No. 1): cl. 8.1.1, 8.1.3, 13.3.1, 13.4 and Tables 8.1, 13.9 and G.2; for the factor γn, DBN V.1.2-14:2018.
The numbers in the calculator are given for information, and the current edition of the codes should be checked before use in a project. The consequence class, γn and γc for a real project are set by the designer: the example uses CC2, γn = 1.05 and γc = 1.0.
What comes next: column base and foundation
Checking the section is only part of the work. The force from the column is taken by the base plate, the anchor bolts and the foundation. The input data for the foundation are covered in the article Foundations for columns, masts and poles. To estimate the mass of the chosen section use the metal weight calculator, and if you need a section with a given W or I, use the section selector.
What to send for agreement
We fabricate steel structures and prepare KM and KMD drawings: see KM and KMD design and steel fabrication. The column calculation is done by the project designer, and we work from the results. Send a drawing or a sketch of the column with its section, length, restraint and forces, and we will discuss the task.
Updated:
Steel column calculator: frequently asked questions
Why does the calculator say the column fails when its strength is sufficient?
Buckling is checked with the smaller of the two φ values, and almost always the weak y–y axis governs. In the example strength is used at 56 %, while buckling without bracing is used at 191 %. Shorten the length between restraints about the y–y axis or choose a section with a larger radius of gyration.
How do I account for bracing or wall girts that restrain the column?
Enter the distance between the restraint nodes in the field “Length between restraints about the y–y axis”. The calculator uses it for that axis instead of the full length, and the x–x axis keeps the full length.
Which buckling curve does the calculator use?
For sections from the sortament, the same as in the column design article: b for an I-beam, c for a channel, a for tubes. For a custom section you choose the curve from Table 8.1.
Which values of γn and γc should I enter?
The values from the article’s example are preset: γn = 1.05 and γc = 1.0. For a real project the designer determines them: γn depends on the consequence class under DBN V.1.2-14:2018, and γc is taken from Table 5.1 of DBN V.2.6-198.
Can I design a column with this calculator?
No. It gives an estimated check of one case, central compression of a solid section. Local stability, eccentric compression, joints and the foundation are checked by the designer, who also makes the final calculation.
Related products: Steel structure design (structural and detail drawings) · Custom steel fabrication
More on this topic: KM Drawings: Contents, Stages, Calculations · What is KMD: meaning and how it differs from KM · KMD Drawings: Contents, Benefits, Cost · KM and KMD Stages: Contents of the Sets · KM and KMD Drawing Rules: DSTU, Specification, Scales · Steel Structure Calculation: Methods and Checks
See also: Steel Column Base
Get a quote for your requirements
Send us your requirements — we will calculate the price and lead time.