ASCE 7-22 Windward Drift

[SteelPE]

I have a project that I am currently working on that is to fall under FM Global Requirements. We are in snow country and it appears as if FM is requiring the roof to be in compliance with ASCE7-22 which uses ultimate snow load vs allowable snow load (which I know and love). Regardless, I am trying to calculate the leeward and windward snow drift (the old upper roof and lower roof snow drift respectively). I noticed that they changed the hd calculation considerable (at least it appears that way).... however, when it come to the calculation for the width of the drift W, there appears to be absolutely no limits on the legth of the windward drift..... they just say to use 8*.75*hd = 6hd.

Is this correct, we just W = 6*hd for windward drifts and there are no longer any limits when hd<hc (like there are still in place for leeward drift)?

 

[ANE91]

hd cannot exceed hc. Refer to Figure 7.7-2. O’Rourke’s textbook corroborates this notion.

 

[SteelPE]

The question is in reference to the drift width W not the height of the drift.

Maybe I didn't make that clear.... I will try to edit my question.

 

[DanKile]

Reading the commentary, yes the windward width is based on the calculated windward drift height, and is not limited by the clear height. The design drift height would stop at the clear height.

 

[Once20036]

I don't want to side track the conversation, but which FM document is referring to ASCE 7-22?

The FM wind document (FM1-54) largely plagiarizes ASCE 7-05. Interesting that their snow document would be SO up to date.