According to DS-EN 1992-1-2 (Danish annex to EN1992-1-2), Annex B2.

Modeling fire exposure for a cross-section entails treating the cross-section as being reduced, meaning the original concrete cross-section is reduced by a damaged zone at the exposed sides. The temperature in a reduced rectangular cross-section θM depends on the fire exposed sides as shown in the table below.

δTBLRδTBδLRθM
110θ2,2h(0,t)
01θ2,2b(0,t)
220θ2,h(0,t)
02θ2,b(0,t)
11θ2,2z(0,t)
321θ2,z(0,t)
12θ2,z(0,t)
422θ2,z(0,t)

For a cross-section with flanges, we determine temperature θM for both the body and the flanges. The cross-section is divided during the calculation according to Section properties, into a body of width b (body width) and height h (original cross-section height) and a flange with width bf and height hf.

For cross-section with variable width or height of flange, we use the value in the middle of the cross-section. For a circular cross-section, the temperature in the reduced cross-section is

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PRE-Stress Documentation