Thickness of damaged zone

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

 The thickness of the damaged zone, for beams, is

The thickness of the damaged zone for columns and walls with 2nd-order effects is

If we set thickness w_y = h/2, otherwise we set w_y = h

If  we set thickness w_x = b/2, otherwise we set w_x = b

The mean value of the concrete compressive strength for the reduced cross-section is determined by

 and

The cross-section is divided into equal cross-section parts. n is an even number greater than 6. For rectangular cross-sections n = 60 are selected.

Where

θ_4,b,h(0, y_j, t) is the temperature in the middle of layer j and

θ_4,b,h(x_j, 0, t) is the temperature in the middle of layer i.

Factor (1 to 0.2 / n) takes into account the uncertainty of a few divisions.

For cross-sections with flanges we use the same calculation method as for rectangular sections, with the determination of a damaged zone for both body and 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 b_f and height h_f.

For circular cross-section, we divide it into n circle rings, each with thickness D / (2n-1), except that the inner circle has a diameter of D / (2n-1). For circular cross-sections n = 20 are selected.

Where

 is the temperature in the center of circle ring i.