blocked diaphragms nailing question

[miguelj1]

hello, can you help me understand the difference between the two nailing categories in the seismic area, (6, 4, 2.5, and 2) vs (6, 6, 4, 3). I understand that there are different cases based on the layout of the panels resting on the members, however what does "other panel edges" mean? If i had a case 1 and 3 type of layout, would I be using the 1st row or 2nd row for my nailing spacing and finding my shear capacities?

Thank you.

 

[enginerding]

Look at the table to the left, that will tell you what row to use: based on the deck sheathing, nails, and width of the joist/truss you are nailing into.

The numbers you list are the nail spacings for the criteria listed. So for Case 3 loading, the continuous edges are parallel to the force and the other panel edges (the ones that are not continuous) are perpendicular. The spacing of those can be greater for the same strength, but what carpenter will want to have different spacings for each different edges?

For Case 1 loading, there are no continuous edges parallel to the loading, so Case 1 is not listed in the top grouping.

So if you were using 1/2" thick Structural 1 sheathing with 8d nails and 2" nominal joists, and you needed a shear of 700 plf, then you would want a nail spacing of 4" along the continuous edge, and 6" on the other edges for 720 plf. And you wouldn't need the full 1/2" thick sheathing for shear, but you'd most likely want that for out of plane loading. Does that help?

 

[phamENG]

So if you were using 1/2" thick Structural 1 sheathing with 8d nails and 2" nominal joists, and you needed a shear of 700 plf, then you would want a nail spacing of 4" along the continuous edge, and 6" on the other edges for 720 plf.

@miguelj1 don't forget that these are nominal capacities - you need to apply a safety or load reduction factor as appropriate for your design method. I missed that an embarrassing number of times when I first started designing wood diaphragms...

For simplicity's sake, I usually go with the lower capacity (continuous panel edges parallel for cases 3 and 4). Granted, I don't do much seismic, but I've found for the decently high winds we have here that until you get to a pretty large aspect ratio it doesn't do a whole lot of good to parse the design out to that level of granularity. If it's the difference between blocked and unblocked, or moving to 3/4" thick sheathing, then I'll look at it, otherwise I'll just use the lesser of the two for both directions.

 

[DaveAtkins]

"Other panel edges" refers to the perimeter of every single piece of sheathing within the diaphragm. I believe some engineers think a panel edge means the perimeter of the entire diaphragm, but that is not true.