Shear Wall Hardware Manufacturer Claims ACI 318 Anchorage Requirements Don't Apply 15

[D.E.N.]

TL;DR:
A shear wall hardware product manufacturer is claiming a steel threaded rod with epoxy anchored to concrete does not need to comply with ACI 318 anchorage provisions. I disagree. If ACI equations are used to check the anchor’s capacity, the product would have a reduced capacity and wouldn’t work as they have designed.

Full explanation:
I am the EOR on a large 5-story light-framed wood apartment building. I designed and detailed all of the shear walls using “typical” hardware, such as coil straps floor-to-floor and holdowns with threaded rods in epoxy at the base. Recently, I received a hardware substitution request from the GC, proposing a different product. Initially, I assumed this was a request to substitute hardware directly from a different manufacturer. However, the submittal proposes a completely different shear wall system.

The proposed system is a proprietary continuous hold-down assembly that connects to the building at the roof level only and anchors to the concrete at the bottom. Its tension capacity is based on testing and comes with a “code approval” report from a certified testing agency. This report, a Technical Evaluation Report (TER), is similar to an Evaluation Service Report (ESR) from other agencies. Due to the proprietary nature of the assembly, no published calculations or test result data are available; only a single allowable tension capacity is provided. The TER specifies installation conditions that must be followed to achieve the published tension capacity.

I have several concerns about this proposed system's ability to resist the required shear wall overturning forces and the proposed load path. Although I have been working with the manufacturer to address these concerns, one aspect of the design remains problematic. Both the manufacturer and the testing agency assert that the system's anchorage into the concrete does not need to be checked using ACI 318 anchorage provisions. The proposed shear wall system consists of a steel cable assembly with steel threaded rods at each end, with the bottom rod embedded in an epoxy-filled hole in the concrete. In my opinion, this anchorage design is not proprietary since it involves a steel threaded rod with epoxy in concrete, which is clearly defined in ACI 318. I would understand the argument if we were talking about a Simpson “LSTHD” Strap-Tie Holdown or MiTek “LSTAD” Foundation Strap, which is a truly proprietary anchorage design since it is just bent steel embedded in the concrete. But this is a steel threaded rod embedded in epoxy that just happens to be attached to the end of a proprietary cable assembly.

The manufacturer has a proprietary epoxy with an ESR report, stating to follow ACI 318-14 Chapter 17. However, the testing agency and manufacturer claim that the ESR for the epoxy is not valid when used with the cable hold-down system. They argue that the ESR only applies when the epoxy anchors steel threaded rods to concrete. It just so happens that the bottom of the cable hold-down system has a steel threaded rod attached to it…

Problem:
Using ACI 318 equations to check the anchorage capacity, I find that the assembly's allowable tension capacity is about 60% less than the manufacturer’s published values, primarily due to concrete breakout. This calculation includes product-specific variables and factors from ACI 355.4 tests, accounting for any proprietary epoxy behavior, which are published in the ESR.

I believe the proposed system’s anchorage must be checked using ACI 318 provisions, as the design closely matches the scenarios covered in the standard. The difference between the published assembly capacity and calculated anchorage capacity is a significant concern that I want to resolve before allowing the product to be used in my building. The testing agency and the manufacturer are telling me not to worry about it since the submittal and the TER are both sealed by PEs in the project state. They claim that since it is a delegated design, I don’t need to worry about how it interacts with my building. I would like to reject the entire system and stick with the original design, but the contractor really wants to use the cable system.

Question:
Have you ever dealt with something like this before? I don’t see how I can allow this anchorage “design” to bypass the ACI 318 requirements just because they are calling a standard anchorage method “proprietary.”

 

[Eng16080]

So, they want to use a substantially different lateral force resisting system than the one you designed? I'm not even sure how I'd design (or check) a system like this where the hold-down is only attached at the roof and foundation. If you had an uplift force somewhere in the middle of the building's height (let's say story 3), if there's no direct hold-down at that location, what happens? Would there be an accumulating uplift force all the way up to the roof? If that's the case, the tension side of the shear wall would actually be in compression, like some kind of post-tensioned column? If you have seismic loads, does this system have an R value like for a conventional wood shear wall, or might it be different?

I don't really have an answer for you on this, except that it all sounds sketchy, especially the anchorage part. Really, you design a threaded rod with epoxy per ACI, except not this time? Doesn't make sense.

Honestly, the more designs I do and the more time I spend reading ESR reports, the less I want to use proprietary products at all. A lot of these products seem to have inflated design values (based on testing or whatever), but if you read the fine print, it turns out the testing is really only for a very specific condition, which might be close to what you have for your building, but is probably not exactly the same. If something were to go wrong, I'm sure they (and their lawyers) would point to the fact that the actual conditions don't match the test conditions. A lot of these products look great on the surface but the fine print really makes it seem like they're trying to limit as much liability as possible.

Personally, I wouldn't trust them even with them sealing it. They're trying to sell a product and they likely have a team of lawyers behind them. You don't. You're the EOR. Ultimately, you own the building structurally if the shit hits the fan. My apologies if this is overly negative. Curious what others here think.

 

[SWComposites]

Sometimes the simplest reply is appropriate: “ No.”

 

[D.E.N.]

Eng16080 - Thanks for the reply. I share the same concerns. Regarding how the system is intended to transfer uplift from intermediate levels, the manufacturer's engineering team told me that it behaves essentially as you described. The tension on the uplift side basically acts like upward "compression" up to the top plate at the roof level and then transfers through the top plate into the cable (with a plate washer on top) and down the cable into the concrete eventually. I actually don't know if they stated an R value in their documentation. I will look into that tomorrow. The TER does say it is approved for use in SDC A-F though.

They can't really give me straight answers on how the anchorage capacity was determined and cannot produce calculations to back their "tests". I asked for test data, but they said that was proprietary and confidential.

I agree with your thoughts on not trusting them, even though they sealed it. Their priority seems to be selling their product, not ensuring the building is designed correctly. It seems like they just count on engineers to blindly accept their "designs" without digging into the details. The further I go down the rabbit hole, the more concerned I get.


SWComposites - I have wanted to just say "no" as soon as I got the submittal, but the GC is convinced that this is the greatest thing since sliced bread. They said that some of their framing subs won't even bid the job unless this system is used. They are saying that this system is waaay cheaper and easier to install. I could see how it would be a desirable system from a cost and installation perspective, but I am more concerned about the reliability and safety of the system. And I have doubts.

 

[phamENG]

You don't have to worry about it because it's delegated? Ha.

1) it's a substitution, not a delegation.
2) "You can delegate authority but not responsibly." Even if it were delegated, YOU are ultimately responsible (seems like you know that, though).

If they can't walk you through a thorough, coherent, and code backed explanation for why they are exempt and have the epoxy manufacturer agree to the same in writing, then you need to tell them to go pound sand.

 

[D.E.N.]

phamENG - Agreed. I sent a detailed hand calc to the manufacturer's engineering team showing the concrete breakout strength using ACI 318 equations AND using their own epoxy values/modifications. The calc showed the ~60% discrepancy in allowable tension. They confirmed they would "review" it and get back to me, but it has been over a week since I heard from them.

I reached out to the testing agency when I wasn't getting anywhere with the manufacturer/supplier and after asking a few questions about how the anchorage capacity was determined, I was essentially accused of being anti-innovation, anti-competition, and potentially violating federal laws for not blindly allowing the system to be used.

I have sunk a tremendous amount of time into trying to vet this system just to try to please the GC and have an open mind, but this is getting ridiculous. If they could prove that I am wrong and provide some actual calculations showing this system works, I would consider using it. I was starting to think I was somehow grossly misunderstanding the situation so it is great to hear others share in my concern/confusion.

 

[Eng16080]

Proprietary? Yeah, ok! If Hilti told me their anchors and epoxy just work but they can't show me the numbers because it's proprietary, I just wouldn't use their products. It's that simple. How stupid do they think us engineers are?

As we all know, the contractor's interests lie primarily in them using the product that's the easiest for them to install. It might as well be rubber bands and hot glue.

 

[D.E.N.]

Eng16080 - Yes! My thoughts exactly. I am meeting with the GC tomorrow afternoon to explain why we likely won't be using this system, so hopefully they will understand the reasoning.

Rubber bands and hot glue, eh? You're not gonna believe this, but I "tested" it and it will work for your application! You'll have to take my word for it though, it's proprietary of course.

 

[bones206]

I feel like perhaps some players in the industry are essentially buying certifications, with testing that is perhaps less than rigorous. I want to give it a name, like “cert-washing”. Is anyone vetting these testing agencies?

 

[hokie66]

Tie bars from top to bottom might work for overturning globally if the wood does not shrink, which is impossible. But what takes the shear at each level? Friction? If this is supposed to be a prestressed shear wall system, you would need some large-scale testing of the whole system to gain any confidence, and I doubt these 'innovators' would want to pay for that. Sounds dodgy to me, and I would just tell them to prove it, otherwise the answer is NO.

 

[WinelandV]

If the GC is determined to use this system, have him create a separate area where the entire system gets installed (concrete, rod, at least 1 level of framing, etc), and then do a pull test (according to w/e standard is used for pull testing anchors, 125% of design, I think, is what's required). Maybe the system's magical load path will actually prove out. Or it will be a spectacular failure.

But at least it won't be "trust me, it's good for it".

Please note that is a "v" (as in Violin) not a "y".

 

[phamENG]

It's a few years old, but here's a good article on the subject in general: Multi-Story Light-Frame Construction: Understanding Continuous Tiedown Systems

The tiedown system with bearing plates only at the top could work. It has nothing to do with shear - we don't depend on HDUs to handle shear loads - just uplift. The article covers it pretty well. It's called a 'skipped-story system'.

TERs are DrJ reports, right? Every time I come across one, it seems a bit sketchy.

 

[XR250]

As Hokie said, shrinkage would be your enemy here. Who is going to re-tension the cable in a year?
Also, what about live load shortening of the framing? In reality, it is not likely to be much but that would also slacken the cable.
The whole idea seems sketch AF.

 

[phamENG]

To be fair, there are automatic take-up devices in a lot of these systems. So maybe they have one. Not sure how it work with a cable, though...

 

[D.E.N.]

bones206 - The idea of "cert-washing" or "pay to win" is my fear. I believe the testing agency is certified but I am unfamiliar with how that process works.


hokie66 - I think the system can work conceptually. As phamENG said, the cables only resist the tension from uplift. We are still specifying traditional sill anchors and fasteners to deal with shear transfer. One of my main original concerns with the system was how it dealt with building shrinkage and how slack was removed from the system. They address this by "post-tensioning" the cable by tightening the nut at the top until a certain amount of thread is exposed. I think the idea is that as the building shrinks, the cable is able to release some of that "pre-load" and remain tight. I think this makes sense from a conceptual perspective, but not sure how it behaves in practice. I have heard stories of cables being exposed in existing buildings and they had significant slack. This idea of "pre-loading" the cable brings up another concern for the anchorage design: sustained tension on an epoxy anchor. ACI 318 has a reduction factor that has to be applied to epoxy anchors that are under sustained tension. This hasn't even been part of my main discussions with the testing agency or manufacturer since I didn't want to stray from the core debate of using ACI 318 at all or not.


WinelandV - That is not a bad idea. The manufacturer claims that all of the anchors are "pull tested" in the field when the "pre-load" is applied, so a more typical pull test used for all other epoxy anchors is not "required". Do you know where the pull test method is defined? If it is in ACI 318, they would probably argue that it doesn't apply to their "proprietary" anchor.


phamENG - Thanks for the article. I have read several from Structure Mag on this topic but I don't think I've seen this one yet. Alfred Commins has written 6 articles about continuous systems that are a good resource:

https://www.structuremag.org/?author_name=alfredcommins

. I'm not sure if all TERs are from DrJ, but this one is.


XR250 - Agreed. The idea of the "post-tensioning/pre-loading" could work I guess, but as I said earlier, I've still heard reports of slack in the system when drywall was removed a few years later.

 

[D.E.N.]

phamENG - They are relying solely on the cable pre-load to take up slack in this system.

 

[phamENG]

Gross. Stop talking to these people and reject the substitution. Also, please post a link to the TER here so we can all run away from it screaming.

There's innovation, and then there's "moving fast and breaking things". Sometimes you can get the former from the latter, but this isn't Silicone Valley. People's lives will be at stake. If they can't prove that it works through trusted methods or methods that can be proven to be trusted, they have no business in this industry.

 

[bones206]

TERs are DrJ reports, right? Every time I come across one, it seems a bit sketchy.

cough, cough THERMOPLY cough, cough

I reached out to the testing agency when I wasn't getting anywhere with the manufacturer/supplier and after asking a few questions about how the anchorage capacity was determined, I was essentially accused of being anti-innovation, anti-competition, and potentially violating federal laws for not blindly allowing the system to be used.

Classic response of the guilty who've been called out. Deny, Deny, Accuse. I'm a Patriots fan so I know it well haha

 

[D.E.N.]

I've attached the cable system TER here:

 

[D.E.N.]

Here is the ESR For the epoxy too: