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What it calculates
- The interaction between axial force and bending moments about both axes, eq. (4.21a) and (4.21b), with the βM factors from the moment diagrams.
- Flexural buckling about both axes and lateral-torsional buckling, with Mcr calculated automatically.
- The cross-section check with axial force, bending moments and shear.
- The governing critical temperature, the fire resistance time, the class achieved and the protection thickness.
Input data
- The section (I/H, SHS, RHS, CHS) and the steel grade.
- Nfi,Ed, My,fi,Ed, Mz,fi,Ed and the shear force in the fire situation.
- The buckling lengths and the moment diagrams about each axis.
- The exposure, the fire curve and the protection.
Example
HEB 240 column in S355 in a braced frame, storey height 4.00 m (ℓfi = 2.00 m about both axes), Nfi,Ed = 800 kN, My,fi,Ed = 40 kNm, constant along the column, Vz,fi,Ed = 20 kN, exposed on four sides, ISO 834 curve.
| Quantity | Value |
|---|---|
| Cross-section class | 1 |
| λ̄y / λ̄z (at 20 °C) | 0.254 / 0.430 |
| θa,cr from flexural buckling, eq. (4.21a) | 618.9 °C |
| θa,cr from lateral-torsional buckling, eq. (4.21b), governing | 595.2 °C |
| Unprotected | 18.1 min, class R 15 |
| Gypsum boards, box protection (λp = 0.20 W/mK), for R 90 | 16.5 mm |
How it is calculated
For combined compression and bending both interaction equations of cl. 4.2.3.5 are checked at each temperature; the critical temperature is the lower of the two. Flexural buckling and Mcr are explained in fire design of steel columns and in fire design of steel beams.
Information material summarising EN 1993-1-2. The results must be checked by a designer; they do not replace the text of the standard, the National Annex or verification by a qualified engineer.