Gross vs net uplift C & C Pressure

[Lutfi]

I am curious as what fellow engineers here consider, to arrive at net C & C uplift pressure, as dead load resisting the gross C &C uplift pressure on roofs?

Regards,
Lutfi

 

[haynewp]

Expected minimum self-weight dead load multiplied by the code reduction factor on that dead load, per the load combinations for wind in the code you are using. The combinations then give me the net uplift. I never include collateral load allowance when checking uplift since it can't be relied on.

 

[lexpatrie]

Collateral or contingency dead loads should probably be ignored or neglected, but there is a 0.6 on the dead load in ASD, practice probably varies.

Some collateral dead loads will quite likely be there (i.e topping slab on precast, poured gypsum floor topping, and so on) other items are less likely to actually be installed (say, shingled roof at 3 psf versus maybe 10 psf for concrete tile), and then "hung loads" that are generally viewed as live loads as they are sporadic.

 

[JLNJ]

My mentor used to call it "reliable". Offset your uplift with reliable dead load.