C&C Wind Load Effective Area
C&C Wind Load Effective Area
(OP)
As I'm going through the "Guide to the Wind Load Provisions of ASCE 7-10" by Mehta and Coulborne I noticed an inconsistency with the regard to the way the effective area for a roof panel is determined. In the one example the roof panel is a 4x8 plywood panel on 24" o/c spaced trusses with the eff. area given as 32 ft2. On the other example the roof panel is 2x8 spanning across trusses that are 48" o/c with the eff. area given as the larger of 4 x 2 = 8ft2 or (4*4)/3 = 5.3 ft2.
If the 4x8 sheet of plywood is spanning the trusses with the long axis perpendicular to the trusses (case 1) shouldn't the span then be 2 ft. The effective area would be the larger of either 2x4 = 8 ft2 or (2*2)/3 = 1.33 ft2.
When dealing with windows, doors and roof panels do you consider the actual area of the component or consider some spanning distance and then compare this distance squared divided by 3 to the trib area? I guess what to use as the effective area for some components had got me a little confused.
If the 4x8 sheet of plywood is spanning the trusses with the long axis perpendicular to the trusses (case 1) shouldn't the span then be 2 ft. The effective area would be the larger of either 2x4 = 8 ft2 or (2*2)/3 = 1.33 ft2.
When dealing with windows, doors and roof panels do you consider the actual area of the component or consider some spanning distance and then compare this distance squared divided by 3 to the trib area? I guess what to use as the effective area for some components had got me a little confused.






RE: C&C Wind Load Effective Area
If you are checking the nailing, a smaller trib area.
If you are checking the rafter then another one as well.
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RE: C&C Wind Load Effective Area
RE: C&C Wind Load Effective Area
RE: C&C Wind Load Effective Area
For example, I do a lot of design of cold formed steel wall stud framing. I use the tributary area for an individual stud (usually H^2/3) to determine the C & C wind load for checking the stud AND connections. A typical slide clip connection which connects a stud to a steel superstructure will be fastened with 2, 3 or 4 fasteners. Should I check the slide clip for the 10 SF C & C load, since an individual fastener will have a tributary area less than 10 SF? Strictly speaking, yes, but I don't--too conservative.
DaveAtkins
RE: C&C Wind Load Effective Area
RE: C&C Wind Load Effective Area
RE: C&C Wind Load Effective Area
C&C Wind Loads - Job 2014-017
Note that the wind forces on the roof panel in zone 3 (overhang) is way up there 88 psf (ASD), but I suppose this is realistic.
Based on this and the APA publication Q225G the allowable for L/240 for 7/16" OSB is only 51 psf. This would then require a thicker sheathing (ie. 15/32 Plywood) which gives a 81 ps allowable for the same spacing and deflection requirement. Note, that this allowable is still below the 88 psf however I think some judgement needs to come into play here otherwise this roof would cost a fortune to sheath.