Shadowing Effect in Fire Resistance Design According to EN 1993-1-2
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For unprotected I‑sections, the standard provides the correction factor ksh according to Equation 4.26a in Chapter 18.104.22.168 (2) to consider the shadowing effect. A term [Am/V]b is used there. This section factor includes Am, which represents the box enclosing the cross‑section (Index b = boxed). In the case of a three-sided fire exposure (a girder with massive ceiling), the flange surface unexposed to fire is not taken into account when determining [Am/V]b.
Three-sided: [Am/V]b = (h + h + b)/V
Four-sided: [Am/V]b = (h + h + b + b)/V
h and b are outer dimensions of the cross-section.
There is no information in the standard regarding the determination of the correction factor ksh for three-sided fire exposure. In the RF‑/STEEL EC3 add‑on module, the correction factor ksh is always considered.
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