“…Using these parameters, the charring depth from the fire‐exposed side can be calculated as follows: where d char,1,n is the notional charring depth along the fire‐exposed side, β 0 is the basic design charring rate, k s,n is the cross‐sectional factor, k 2 and k 3,1 are the protection factors for the charring along the fire‐exposed side in the protection and postprotection phases, respectively, t ch is the start time of charring from the fire‐exposed side, t f is the fall‐off time of the cladding, t is the is the fire exposure time.…”