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What it calculates
- The bending resistance with the adaptation factors κ1 and κ2, about the major or the minor axis.
- Lateral-torsional buckling, with the elastic critical moment Mcr calculated automatically.
- Shear and the interaction between bending moment and shear force.
- The governing critical temperature, the fire resistance time, the class achieved and the protection thickness.
Input data
- The section (I/H, CHS, SHS, RHS) and the steel grade.
- The bending moment Mfi,Ed and the shear force Vfi,Ed in the fire situation.
- The distance between lateral restraints and the moment diagram, for lateral-torsional buckling.
- The exposure (for example three sides, below a concrete slab), the fire curve and the protection.
Example
IPE 300 beam in S275 below a concrete slab, exposed on three sides, top flange restrained by the slab (no lateral-torsional buckling), My,fi,Ed = 80 kNm, Vz,fi,Ed = 40 kN, ISO 834 curve.
| Quantity | Value |
|---|---|
| Cross-section class | 1 |
| Unprotected: κ1 = 0.70, μ0 = 0.324, θa,cr | 652.1 °C |
| Unprotected time (Am/V = 187.7 m−1) | 16.6 min, class R 15 |
| Protected: κ1 = 0.85, μ0 = 0.393, θa,cr | 622.3 °C |
| Mineral fibre spray (λp = 0.12 W/mK), for R 60 | 12.0 mm |
How it is calculated
The moment resistance is reduced by the adaptation factors κ1 (temperature distribution across the section) and κ2 (along the beam); for a beam that can buckle laterally, the critical temperature comes from the lateral-torsional buckling check. All three checks are described 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.