Anchor Spacing for Wood Stud Walls subject to Lateral/Uplift Loading

[abusementpark]

I was reviewing section 4.4 of the AF&PA SDPWS-2008 - Special Design Provisions for Wind and Seismic standard, which covers wood structural panels designed to resist combined shear and uplift from wind. In section 4.4.1.6. it states that bottom plate "anchors shall be spaced at 16" on center or less". I don't see this tight spacing requirement anywhere else in the code.

Why would this only apply when you are using wood structural panels to transmit uplift? What if you are sending the uplift in a shear wall directly through the studs through toenails or hurricane ties? How is that any different for the combined shear and uplift on the anchors?

BTW, the document can be viewed here.

http://www.awc.org/standards/sdpws.html

 

[woodman88]

Read the commentary section C4.4.1.6. The problem appears to be the bottom plate failure to transfer the uplift from the sheathing to the archor bolts at a greater spacing than 16" oc.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[msquared48]

I imagine then that with a 3X or 4X bottom plate that the spacing could be increased...

Mike McCann
MMC Engineering

 

[abusementpark]

Read the commentary section C4.4.1.6. The problem appears to be the bottom plate failure to transfer the uplift from the sheathing to the archor bolts at a greater spacing than 16" oc.

But shouldn't then that requirement also apply if you are using hurricane ties on each stud to transfer uplift? I don't see where that is much different as far as how the bottom plate transfers combined shear and uplift to the anchors.

I imagine then that with a 3X or 4X bottom plate that the spacing could be increased...

Is this common in some parts of the country? I practice in the Gulf South and I have never seen that. In fact, I'm not sure if solid 3x and 4x members are readily available. We usually "gang" 2x members to make bigger beam and column sections.

 

[msquared48]

They are available where I am, and the 3X's are used in shear walls where high shear loads and staggered nailing is present in the plate. They also allow the anchor bolts to have a greater spacing. FYI, I have also used double 2X plates.

Mike McCann
MMC Engineering

 

[jaypartain]

If you use hurricane ties to transfer the uplift into the bottom plate you still have to transfer that load into the foundation. You would be required to design the sill plate for this load. Instead of leaving this up to the Engineer, the SDPWS just prescribes anchor bolts at 16" o.c.

Jason A. Partain, P.E.

http://www.myconstructionfinds.blogspot.com

 

[abusementpark]

If you use hurricane ties to transfer the uplift into the bottom plate you still have to transfer that load into the foundation. You would be required to design the sill plate for this load.

And how do people usually account for the twisting action on that plate since the hurricane ties frame into the side of the plate and the anchors are usually centered on the plate?

Instead of leaving this up to the Engineer, the SDPWS just prescribes anchor bolts at 16" o.c.

I find it odd that they do it for for this application and not others.

 

[msquared48]

"And how do people usually account for the twisting action on that plate since the hurricane ties frame into the side of the plate and the anchors are usually centered on the plate?"

If this is of concern, then alternate the hurricane ties to either side of the plate.



Mike McCann
MMC Engineering

 

[jaypartain]

If you review Section 4.4.1.6 Item 2 you will find how the SDPWS acounts for this rotation. I would use this as a starting point for accounting for rotation of the sill plate.



Jason A. Partain, P.E.

http://www.myconstructionfinds.blogspot.com

 

[a2mfk]

Abusement- Are you dealing with SIPs? You can use double 2x base plates like Mike suggested, and then design it for whatever anchor spacing you can make the numbers work for... Is someone calling you out on this (reviewer) or are you just concerned with that requirement, which sounds prescriptive at best.

 

[abusementpark]

Abusement- Are you dealing with SIPs?

No.

Is someone calling you out on this (reviewer) or are you just concerned with that requirement, which sounds prescriptive at best.

I'm just concerned with the requirement.

Really, I am curious about the twisting action on the plate due to sheathing or hurricane ties being attached to the side of the plate and how most engineers have been handling it? When using hurricane ties, do most stagger the side of attachment to prevent the twisting action?