Full Height Threaded Rods used for Shear Wall Hold-down

[NFExp]

What are your thoughts on using full height threaded rods for plywood shearwalls. Full height threaded rods have been the industry standard in my area for years however engineers and contractors do not use skrinkage compensators. I have read that if shrinkage occurs and there is a 1/4" gap between the top plate and threaded rod washer, the shearwall loses 70% capacity.

I'm just wondering if anybody could justify using full height threaded rods without skrinkage devices?

 

[bylar]

I specify them all the time for log homes and recommend
AT75 Auto take-up devices by Commings Manuf. Inc., Friday Harbor Wa.

 

[msquared48]

Same here. Met the owner of the Commings product in my office 15 years or so ago. Works great.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[asixth]

Can you please elaborate on shrinkage devices? I have not seen anything in my part of the world which would classify as a shrinkage device.

 

[hokie66]

I'm interested as well. Searched, but no luck.

 

[mmillerpe]

I am not sure whether or not Simpson Strong Tie goes international or not, but they have a line of products called the ATS system which included shinkage compensators (Simpson refers to these as Take Up Devices or TUD's) More info can be found at:

http://www.strongtie.com/products/ats/index.html?source=topnav

 

[RockEngineer]

Here is Commins Web page

http://www.comminsmfg.com/

 

[NFExp]

bylar & msquared48

Do you specify shearwalls without shrinkage compensating devices?

 

[RockEngineer]

Earthbound Inc, Monroe, WA also has a system. I have used their Earthbound Impasse Device but now they seem to be using a new device called their slackjack with is similar but can allow for more shrinkage and higher loads.

http://www.holdown.com/

 

[JoshPlumSE]

I would say that this issue is very dependent on the aspect ratio of the wall.

For a narrow tall wall, the effect of shrinkage will drammatically increase the % of "hold down deformation" that occurs in the wall. That will make it much more flexible. If drift / deflection is a major factor in the final design then you may be in trouble.

The shrinkage term will not have nearly so much of an impact on long, squat walls. That's because the hold down term does not get magnified in the same way on these walls. Or, at least it results in a lower percentage change in the wall stiffness.


Also, my impression was that the deflection take up devices are mostly a seismic / california thing. And, that you would not nearly as likely to see these in other parts of the US.

 

[RockEngineer]

Two places I have used these devices.
1. Tall narrow heavily loaded shear walls in multiple story buildings (high wind or seismic lateral loads).
2. Log homes where you are trying to use friction between the logs as the first failure mechanism for lateral loading and bearing on the rods as the secondary failure mechanism. The devices give you a consistent loading for friction if you find ones that have enough take up to compensate for log shrinkage.

 

[NFExp]

JoshPlum

I tend to agree with you.

I recently found an article written by Ronald F. Nelson in structure magazine where he says that the loose shearwall hold downs may reduce "initial wall stiffness but had no effect on ultimate capacity"

 

[dik]

Longitudinal shrinkage of dimensioned lumber is relatively small with shrinkage happening with the top and bottom plates of the wall construction. I wouldn't think it would be a problem unless, like British Columbia, Canada where they are permitting 6 storey wood framed buildings in a seismic area...

With log construction I usually use an adjustable tie for 'settling' purposes. The logs shrink radially with drying.

Dik