Joist Spacing Under Drift

[skbeng]

I am trying to design joist spacing under drift load. I know its more of a trial and error to find the space that works but I can't remember how to go about doing this. Does anyone have any good examples to share or where I can find one.

Thank you.

 

[UcfSE]

Trial and error: guess a value to begin with and check it. If it works, you guessed well and may move on, otherwise refine your guess and iterate.

 

[jike]

Figure out the drifting loads plus base snow load plus dead load. Draw the tapered load diagram showing the max. and min. loads and the drift length. Using the max. load, find out the max. length the deck can span. Select a deck. Go out that distance and figure the DL+LL at that point on the tapered diagram. Multiply that load times the joist spacing and select a joist. Repeat the process as many times as necessary until you are in the normal snow load area.

 

[DaveAtkins]

Some other points to keep in mind--
K series joists can only support 550 plf maximum.
To keep things simple, I would use one spacing under the entire drifted snow width, then the typical spacing everywhere else.

DaveAtkins

 

[COEngineeer]

ASCE has a god explanation. I dont understand what you mean by trial and error? I just use a free software (bc calc) to figure out the joist size. I figure out the drift load depending on the size of the roof, the height of wall, the size of the upper roof (leeward or windward drift). See ASCE section 7.7.

http://www.krmconsultants.com

 

[skbeng]

Thanks for the input. Some helped to refresh my memory and the others were different ways to go about it.