Pg = 5 psf 2

[jike]

Since I work mainly in northern climates I have a couple questions when dealing with snow loads where Pg = 5 psf.

According to ASCE 7-02, Pf = (I)Pg = 5 psf but then I have to add 5 psf rain on snow surcharge. When calculating drift, do I use Pg = 5 psf and Pf = 5 psf or Pg = 10 psf and Pf = 10 psf or something else? I am confused!

 

[haynewp]

When adding drift to the balanced snow load you would develop the drift load based on pg=5 psf. Then add the pf=5psf plus the 5 psf rain on snow surcharge to the roof. Ground snow stays at pg=5psf.

 

[fasboater]

Haynewp,

I believe you mean flat roof snow load Pf. Because rain on snow surcharge is not required when you use drift loads. Although I do agree that the design load (S) would be the Pf + rain on snow surcharge.

JB

 

[jike]

Where does it say that the rain surcharge is not required for drifting?

 

[fasboater]

Sction 7.10 of the 2005 ASCE "This rain-on-snow ugmented design load applies only to the balanced load case and need NOT be used in combination with drif, sliding, unbalance, or partial loads." pg 83

JB

 

[haynewp]

Yes for the drift area the rain is not required, the rest of the roof is balanced plus rain.