Canopy Drift Loads
Canopy Drift Loads
(OP)
I am designing a precast building with a small (cantilevered 5'-0") canopy at one end. The building is approximately 1300' long and 40'-0" tall.
The drift load would be around 200 psf and 40' long, then truncated to the 5' canopy according to what I can find in the ASCE. This would usually not cause any problems with the PC, but the canopy is on a 2'-6" spandrel panel which has a large amount of torsion due to the drift.
It doesn't make sense to me that the snow will stack up perfectly 11'-0" up the side of the building. Is there a maximum angle the snow will accumulate from the front edge of the canopy? Or any other way around using the 200 psf?
Thanks for the information.
The drift load would be around 200 psf and 40' long, then truncated to the 5' canopy according to what I can find in the ASCE. This would usually not cause any problems with the PC, but the canopy is on a 2'-6" spandrel panel which has a large amount of torsion due to the drift.
It doesn't make sense to me that the snow will stack up perfectly 11'-0" up the side of the building. Is there a maximum angle the snow will accumulate from the front edge of the canopy? Or any other way around using the 200 psf?
Thanks for the information.






RE: Canopy Drift Loads
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Canopy Drift Loads
Thanks for your reply.
RE: Canopy Drift Loads
Your 29' drop makes it even more unreasonable to stack that high.
How wide is your canopy?
RE: Canopy Drift Loads
http://www.eng-tips.com/viewthread.cfm?qid=222195
RE: Canopy Drift Loads
I remember seeing a max angle the drift will go up in the old BOCA codes but I can't find anything in the new codes about it.
RE: Canopy Drift Loads
RE: Canopy Drift Loads
RE: Canopy Drift Loads
Basically the projected area cut off by the wall above the canopy would accumulate a certain volume of snow during the storm - this snow is in turn dumped onto the canopy. I imagine it as the snow coming down at an angle and hitting the face of the wall and droppins down to the canopy. The snow accumulation would look like a drift, forming an angle due to the angle of repose of the snow.
I think in many circumstances this accumulation could tend to be very high - if the conditions permited. This all assumes wind doesnt disturb it, the snow falls in the worst case direction, etc.
just my thoughts that, again, are not spelled out in any code that I know of...
RE: Canopy Drift Loads
RE: Canopy Drift Loads
RE: Canopy Drift Loads
Hope this worked.
Jim
This is not quite an 11 foot drift on a 5 foot canopy but I guess the dormitory building is not 1352 feet long either.
RE: Canopy Drift Loads
RE: Canopy Drift Loads
I had always assumed that the truncated requirement was due to code conservatism, but it does happen now and then, I just don't any clean photographs of a nicely truncated drift.
Jim,
RE: Canopy Drift Loads
RE: Canopy Drift Loads
With that said, by ASCE, I believe I'm stuck with the ridiculous 11' drift load.
I too would like to see some current pictures of canopies loaded with that much snow. We have gotten about 20" of snow in the last week along with strong winds but I have not seen any to document.
RE: Canopy Drift Loads
RE: Canopy Drift Loads
RE: Canopy Drift Loads
RE: Canopy Drift Loads
RE: Canopy Drift Loads
Jim
RE: Canopy Drift Loads
WCW