Fire resistance check (Beams: EC3 Eurocode)

Tekla Structural Designer
2021
Tekla Structural Designer

Fire resistance check (Beams: EC3 Eurocode)

 

Scope

This check determines the mechanical resistance of a steel beam subjected to major axis bending in case of fire during the required time of exposure in accordance with EN 1993 & national annex for the UK, Ireland, Singapore, Malaysia, Sweden, Norway, Finland or the recommended Eurocode values.

The check can be applied to non-composite, simply supported rolled steel beams, which:

  • may be unprotected (bare steel) or protected,
  • may be exposed on 3 (under a slab) or 4 sides.

The check is applied for gravity load combinations only.

Temperature domain verification uses the Critical temperature method as described in EN 1993-1-2, Cl 4.2.4

Limitations and assumptions

The following limitations and assumptions apply:

  • The calculation is limited to a restrained single-span beam in bending. If  the check is performed on an unrestrained beam and the check passes the result is not valid. (In this situation manual checking of the unrestrained beam might show it is ok.)  For further details see: PBTSD-2307-01 

  • For beams with web openings, the suitability of the check is a matter of engineering judgement. For further details see: PBTSD-2307-03 

  • As per EN 1993-1-2, Cl 4.1(3) simple calculation models are simplified design methods for individual members, which are based on conservative assumptions.

  • According to EN 1991-1-2 Cl.3.1 (10) the standard temperature-time curve is used to calculate gas temperature –curve as described in EN 1991-1-2 Cl.3.2.1.

  • The calculation considers that shear buckling resistance according to section 5 of EN1993-1 can be ignored so it doesn’t check it as per cl.6.2.6(6) EN 1993-1-1.

  • A conservative approach has been taken regarding the fire moment resistance of the steel beam at time t so it’s limited to the ultimate moment capacity of the beam.

  • The effects of indirect actions are not considered. These actions, such as internal forces and moments induced in the structure by deformations and restrained thermal expansion, do not need to be considered when the fire safety is based on the standard –temperature time curve.

  • The shadow effect caused by local shielding is not taken into account, therefore the shadow effect factor is conservatively taken as 1.

  • For Malaysia & Ireland check is as per UK NA.

  • Fire protection properties (self weight of fire protection material) are not considered for loading and analysis.

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