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Anchorage for Uplift

Anchorage for Uplift

Anchorage for Uplift

(OP)
This morning I was re-reading Section 4.4 of the SDPWS 2008 and subsection 4.4.1.6 stood out. In particular was the sentence, "Anchors shall be spaced at 16" on center or less". This sentence has me a little confused. I generally call out my anchor bolts and spacing based on in-plane and out-of-plane lateral loads to the walls. If these loads are negligible I utilize a max. spacing of 48" to account for the high wind of the locale (prescriptive approach based on WFCM high wind guides). This 16" on center specification in section 4.4.1.6 is something I haven't noticed or at least ignored previously.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Anchorage for Uplift

(OP)
If I am understanding it correctly, the purpose of Section 4.4 of the SDPWS is to help designers eliminate the vertical strapping between floors for multi-story buildings by relying on sheathing splices and capacity of the sheathing as given in tables 4.4.1 and 4.4.2. I am finding that trying to control where these splices will occur is not realistic. When the contractor frames up the house and applies the sheathing nine times out of 10 the sheathing gets terminated at the double top plate and does not occur over the rim joist or across studs as shown in Figure 4I. Additionally, Fig. 4J is too much work for most of my contractors, lets face it they are creatures of habit.

I am wondering what other's experience is with the provision of Section 4.4 and what is the best practical solution. For now I've gone back to vertical straps between floors for uplift since the inspector can verify those quickly and they won't get disregarded.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Anchorage for Uplift

Good day Medeek.
You are correct in that AF&PA SDPWS section 4.4 is for using the sheathing to resist net uplift without the need for straps. I have used it but only on commercial project that had special inspection. One recent example was a fire station with 72' clear span trusses. The net uplift to each truss was over 800# and required H10a hurricane clips. I talked with the tech info line at AF&PA and was told that the 16" anchor bolts was because that is what was tested. This is a new section and they always start out conservative. He told me that the next version should a bit less stringent.

my application was a one-story structure with 18' walls so all the splices were at blocking using the detail per figure 4J.

RE: Anchorage for Uplift

Medeek,

See APA SR101C (Feb 2015). In that document, there is guidance on AB spacing for combined shear and tension forces. You have to sign up at APA's website, but it is free to do so.

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