PFP. Partly protected
The default protection assumes that all surfaces of the cross section are covered with the same PFP. However, in special cases, such as integrated deck-plating and deck girders, the over side is often left unprotected of practical reasons. The sections are fully protected for fires from below (see Figure-1).
In general, the heat flux hitting the deck is lower than the heat exposing higher up in the actual fire compartment. A typical deck-flux level is used in this example (100 kW/m2), and the flux varies over time.
Figure 1 : Partly protected deck-girder system
The PFP Performance is defined by the "U-value" [ W/m2K ] using the command INSULPAR. The PFP is assigned to element using the command ELMINSUL.
The command EXP_ELEM is used to define both section parts with PFP and Exposed/Unexposed surfaces, (On the upper flange, web and lower flange).
The following codes are used to identify the PFP and exposure:
Since the fire is exposing only the over side of the upper flange, the "Exposure code" is set to 1 for the upper flange and 0 for the web and lower flange. The PFP code is 2 for the upper flange (PFP on underside only) ,and 3 (both sides) for the web and lower flange.
See input files
=> Fahts Control File
=> Structural File
Figure 2 : I-Girder with no PFP on overside and exposed to 100 kW/m2 from above.