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Methods for fire resistance analysis

500°C isotherm method

This method is based on the chapter B.1 of EN 1992-1-2. It may be used in combination with standard or parametric temperature curve. The minimum member width according to the table B.1 of EN 1992-1-2 has to be respected.

Analysis procedure:

• The calculation of the temperature distribution with the help of finite element method
• The determination of the new effective cross-section by excluding the concrete outside the 500°C isotherm. The material characteristics aren't reduced for this cross-section
• The determination of the reduced material characteristics for all bars of the reinforcement according to their temperatures
• The verification of the new effective cross-section using geometric and material characteristics mentioned above. The reinforcement placed outside the 500°C isotherm is considered in the analysis.

Zone method

This method is based on the chapter B.2. This method provides provides more accurate results, mainly for the columns. It may be used only in combination with the standard temperature curve.

Analysis procedure:

• The cross-section is divided into specified number of parallel zones (default count is 100)
• The mean temperature and the corresponding mean compressive strength f_cd(Θ) is calculated in every zone
• The mean reduction coefficient for a particular section k_c,m is calculated using expression (B.11):

• The thickness of the damaged zone is calculated. The following expression (B.12) is used for member types "Beam" and "Slab":

The following expression (B.13) is used for member types "Column" and "Wall" and for all other members that have the buckling verification switched on: