Question about National Building Code of Canada snow loads 2

[lilylucyleo]

Hello everyone,

I am reading the NBCC2015 on Clause 4.1.6.3 "Full and Partial Loading". I am not quite clear what the "partial loading" is, and how to apply it. To my understanding, it is a type of uniform loads other than nonuniformly distributed load. But the code says "flat roofs and shed roofs, gable roofs of 15° or less, and arch or curved roofs shall be designed for the specified uniform snow load...,...distributed on any one portion of the loaded area and half of this load on the remainder of the loaded area, in such a way as to produce the most critical effects on the member concerned." My questions are:

1). Does this mean there are three types of snow loads, uniformly load in the forms of both fully and partial loadings, and nonuniform load?
2). How to apply the partial load to "one portion" of the area? I mean, how to determine which area to apply the full and which area for the other half?

Thanks a lot,
Fiona

 

[gwynn]

Do you have just the NBCC or the commentaries as well? Much of the load requirements regarding full and partial loading is located in the commentaries (not sure why they are not part of the code itself, as you can't do part 4 design without them). I would look it up, but I don't have a copy with me.

 

[allgoodnamestaken]

You need the structural commentaries on Part 4, division B, to get the details on the snow loads.

http://www.nrc-cnrc.gc.ca/eng/publications/codes_centre/2010_user_guide_nbc_part4.html

 

[ajh1]

The 2015 code does a better job of getting all the really pertinent details into the code itself, rather than the Commentaries. With luck the Commentaries book will be out sometime this fall. In looking at the 2010 commentaries on this section, it really only indicates two things:
1) It is a judgment call based upon your building configuration to determine which portion gets full load and which gets half.
2) The requirement does not imply full checkerboard loading.

For example if you have a two-span continuous beam, you would want a load combination that put 100% of the snow on one of the two spans and 50% on the other, then a second combination that does the reverse. For a 4-span continuous, probably something like spans 1,2 get full, 3,4 get 1/2; or 1,4 get full, 2,3 get half. The second item above would suggest you don't need a 1,3 full, 2,4 half pattern.

Buildings with gable conditions over 15 degrees are getting boosted due to over-ridge full and partial snow loads per Article 4.1.6.9, so are exempt from the Article 4.1.6.3 provision.

 

[lilylucyleo]

Hi ajh1,

Thanks for your explanations. It helps me a lot. I agree with you that NBC2015 improves a lot by putting details into it instead of commentaries.

Regards,
Fiona