ATFP window stuff

[FeSE]

thread507-268076

Note that there is a new UFC out for ATFP. Does anyone know how to interpret B-3.1.4.1 with respect to the tributary area increase factor? My only guess as to what this means is that the whole wall should be loaded with blast pressure just like wind. Meaning the trib increase factor on the supporting elements makes the load on the supporting element include the reaction from the window?

If this is the correct interpretation, then how should the load be calculated? Should we just use astm f-2248? That's for glazing.. There's a blast pressure equation in NCMA TEK 14-21 for peak blast pressure, but peak pressure is waaaay higher than equivalent static pressure. Also, using astm f2248 for the whole wall would be conservative because most wall structures would be waaay more ductile than glass.

Also, does anyone know how the 3-second equivalent design load in ASTM F2248 was created? Are there equations?

 

[haynewp]

I don't use the static method that much but it now appears to be requiring you to take the capacity of the typical structural member that you get based on conventional loads, and amplify it by the trib area it is receiving from the adjacent window and wall above and below the window (for example when looking at a wall). I don't see that ASTM F2248 is required here for what you are asking. It looks independent of the blast requirement of the glazing and wall altogether now so I am not sure why it is even in there, but this can only be used where you meet or exceed the conventional construction standoff.