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Foundation Connection: The Weak Link [mid-rise wood framed construction]

jar546

jar546

CBO
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Oct 16, 2009
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There is no doubt to me that the engineering and execution of the work for the embedded anchor rod is the Achilles heel of this system. Who is seeing this in their area? This goes beyond seismic and is very relevant for wind loads.

 
A little unclear as to what specific you see as the failure modes

The video seems to be more attuned to situations where there is significant uplift due to wind. In California it is common practice to use holdowns connected to a 4X or 6X member at the end of shear walls. Remember we are focused on earthquakes. While wind loads are considered global wind uplift tied to foundation is seldom considered. It probably helps that we do not have the hurricanes and tornados common to other states.

Agree that installation is critical. Still my perception is that between building department inspectors, special inspectors , and engineers visits to site compliance with the permit drawings is fair to good.
 
jar546 said:
There is no doubt to me that the engineering and execution of the work for the embedded anchor rod is the Achilles heel of this system. Who is seeing this in their area? This goes beyond seismic and is very relevant for wind loads.

Click to expand...
I see these used all over the country. QA/QC does not seem to be a problem. Are you seeing failures? I have not.

These systems (there are many) are used where you have net uplift. Engineers try to design their shear walls where they have enough dead load to counteract the overturning but it isn't always possible or economical. These systems solve the overturning issue.
 
redeyedfly said:
I see these used all over the country. QA/QC does not seem to be a problem. Are you seeing failures? I have not.

These systems (there are many) are used where you have net uplift. Engineers try to design their shear walls where they have enough dead load to counteract the overturning but it isn't always possible or economical. These systems solve the overturning issue.
Click to expand...
Many times frame walls don't have enough dead low to overcome the uplift by I think the only rods at work are the ones that have springs and retention themselves when the wood shrinks. I try not to design wood structures to resist high wind loads as there's thousands of areas that can be deficient. Sometimes you can pull the rod connection right out of the slab because it hasn't been prepared properly.
 
chief-inspector said:
Sometimes you can pull the rod connection right out of the slab
Click to expand...
Thirty years ago I was a carpenter on a five story wood hotel at Sacramento Ca. At the elevator shaft was a group of all-thread rods for a brace. The rods were the largest that I had seen in use... probably close to 2"dia. There was a plate and nut at the bottom.
When it came time to frame the brace it was discovered that the rods were not sticking out of the concrete far enough. No problem, they are after all, threaded.
 
Yikes said:
I think similar systems (such as Z4 by Mitek) have been around long enough that they have worked as designed during actual seismic events.
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Yes that's when the failures occur as I have seen many many pull-outs in hurricanes and tornadoes. I have also seen CMU Bond beans ripped out too.
 
ICE said:
Thirty years ago I was a carpenter on a five story wood hotel at Sacramento Ca. At the elevator shaft was a group of all-thread rods for a brace. The rods were the largest that I had seen in use... probably close to 2"dia. There was a plate and nut at the bottom.
When it came time to frame the brace it was discovered that the rods were not sticking out of the concrete far enough. No problem, they are after all, threaded.
Click to expand...
Yes but unfortunately most rods have no provisions for wood and building shrinkage and become loose but I guess it's better than nothing. When I didn't inspections five or six years later on rodded structures once the wall was open I can move the rod around 4 in. There should be an access hole so you can tighten the coupling or have a key way for a hex wrench.
 
The systems I've seen here in California are like the ones you've described in post #6, with springs that ratchet the system tighter as the wood shrinks.
Two months ago we did a remodel on a 15 year old building, and discovered one of these where it didn't show up in the owner's record drawings.
Despite all the years of building shrinkage (and despite the studs not having a "KD-19" stamp on them), the spring had done its job and the rod was not loose.

By the way, that does point out one downside of using rods vs. holddowns: it's really had to engineer a workaround if you need to move a wall during a remodel, without affecting an entire stack of apartment units.
 
Yikes said:
The systems I've seen here in California are like the ones you've described in post #6, with springs that ratchet the system tighter as the wood shrinks.
Two months ago we did a remodel on a 15 year old building, and discovered one of these where it didn't show up in the owner's record drawings.
Despite all the years of building shrinkage (and despite the studs not having a "KD-19" stamp on them), the spring had done its job and the rod was not loose.

By the way, that does point out one downside of using rods vs. holddowns: it's really had to engineer a workaround if you need to move a wall during a remodel, without affecting an entire stack of apartment units.
Click to expand...
Yes that can be a problem so you can use a couple studs nailed together and strapped top and bottom to act as a tension tie.
 
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