The requirements shall apply to steel building elements designed to exhibit a required fire-resistance level (FRL) as per the relevant specifications.
16.1.1
For protected steel members and connections, the thickness of protection material (hᵢ) shall be greater than or equal to that required to give a period of structural adequacy (PSA) greater than or equal to the required FRL.
16.1.2
For unprotected steel members and connections, the exposed surface area to mass ratio ( ) shall be less than or equal to that required to give a PSA equal to the required FRL.