Horizontal Shear

[EIT2]

RE: APA Table: Diaphragms: Recommended Shear for Horizontal APA Panel Diaphragms ...

We need to analyze the load applied to both the length and width of sheathing.

"Case 1" represents the sheathing layout I use, but there does not seem to be a corresponding Case with the load parallel to, and the framing perpendicular to the sheathing length. Until a year ago, I had considered "Case 3" to be that particular Case. Then someone pointed out that, the word "Framing" is pointing to the line parallel to the sheathing length. If this is correct, then the width of the sheathing is spanning 48". With the exception of "Case 3", all the other Cases have the framing at 24" oc and perpendicular to sheathing length. I think "Case 3" is an error. I believe the word "Framing" is actually pointing to Blocking.

Any thoughts or comments?

Thank you!

 

[ERV]

EIT2,

UBC 97, Table 23-II-H, on a fully blocked diaphragm, it does not really matter as long as the required nailing is met. Boundary nailing and panel edges control shear and field nailing controls lateral support of panels.

 

[EIT2]

Thank you! But, I design for unblocked diaphragms unless the load is too high. Considering a relatively simple, <=2:1 rectangle, low-rise structure, it is rare that the load demands a blocked diaphragm.

My question regarding the integrity of the &quot;Case 3&quot; example remains - is it correct? Is the word &quot;Framing&quot; actually pointing to blocking? Would anyone actually span the sheathing width 48&quot;? Considering any snow region, would anyone use 48&quot; oc frame spacing for single-ply, <=19/32 horizontal diaphragm sheathing? According to APA tables, you cannot!

Am I missing something?

Thank you!

 

[EIT2]

Yes! I AM missing something.

I called APA and have been informed that the important issue is not so much the sheathing layout configuration, but, rather, the load parallel to continuous panel joints as at &quot;Case 6&quot;.

ERV, your comment &quot;... panel edges control shear ...&quot; was sufficient. I did not understand at that time. I do understand now.

Thank you!