Post Installed Anchorage to Masonry Wall
Post Installed Anchorage to Masonry Wall
(OP)
I am trying to design the anchorage of wood shear walls down to 12" CMU basement walls. A few of my walls have relatively large uplift forces (≈18 kips ASD). I've seen posts here about lapping the a cast-in threaded rod with rebar in the wall to achieve larger loads than the typical masonry anchorage equations allow. However, I'm wondering if the same principles could be used for drilled and epoxy bars. I've used this methodology before in concrete using Hilti's info on Appendix D vs. development length designs in concrete. Would using a similar approach (with appropriate masonry equations and principles) be a potential solution in my case?
Thanks for your help!
Thanks for your help!






RE: Post Installed Anchorage to Masonry Wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
I don't want to apply the same equations and code from concrete to masonry. Rather I'm looking to see if it is within reasonable assumptions to use a similar approach to drilled and epoxied bars in masonry.
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
What I mean is that, unless I'm egregiously mistaken, this is an anchorage problem in addition to a development problem. And, to my knowledge, we don't have an established method for dealing with masonry anchorage problems of this sort in north america (obviously we can handle little cast in stud groups etc). I have been applying ACI Appendix D to masonry situations where the masonry is solid grouted. I'm sure that there are differences between concrete and masonry behavior in this but, baring any other guidance, that strikes me as the best available. Sometimes I'll also just look at it as a wedge of block that has to be yanked out while developing one way beam shears on the sides of the frustum. I've done this mostly in Canada where we don't submit calcs and can therefore do whatever. I've also done it a few times on the west coast of the US for shear wall hold downs into CMU grade beams. So far so good there too. Reviewers seem reluctant to call you out on things that they have no idea how to do themselves.
In my opinion, you really have to be careful with manufacturer info in this area. They sell more anchors by providing high capacity anchors. As a result, they often seem willing to let designers assume that development is the answer to their problem when in fact it is anchorage that needs to be considered. Lies of omission essentially. I know that sounds harsh but that's how I see it.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Post Installed Anchorage to Masonry Wall
For clarity - when I say anchorage I'm talking about the splitting and failure cone type checks you run for small(er) embedment cast in anchors.
RE: Post Installed Anchorage to Masonry Wall
I would certainly say that there ought to be some strong parallels.
Good on you for recognizing this. In my experience, upwards of 2/3 of all structural engineers don't correctly recognize the rather critical difference between development and anchorage. I've had numerous, protracted debates about that here. And for anyone that might be wondering, I'm not fishing for a repeat performance in this thread.
The process that you're describing is somewhere between anchorage and lapping in my opinion. I'd be tempted to follow the pre-APPD rules for anchor bolts. You know, where you imagine yourself yanking out a 35 degree cone and you follow some rules about how far apart things that are "lapped" can be etc? AISC DG01. Frankly, I don't think that there really is an "official" way to evaluate this connection at the scale of load you're considering.
Another path is to get your washer plate sufficiently under a bond beam that you can trace a convincing load transfer path over to the adjacent, reinforced vertical cells. Obviously, interior conditions are a lot more fun than corners. Damn corners...
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Post Installed Anchorage to Masonry Wall
Even if they could procure the right drillbit, and drill 48", I would like to see the next steps. I imagine it would be a futile attempt to remove the debris. I dont think even compressed air could spit up dust from the bottom of a 48" hole, much less hilti's little handheld pump blower.
Then, to properly fill a 48" deep 1" diameter hole with epoxy. Even with a careful and competent contractor, it seems like it might be a bit of a stretch.
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Post Installed Anchorage to Masonry Wall
RE: Post Installed Anchorage to Masonry Wall
I'm not sure why you would use Appendix D vs ACI 530 for cast in anchors. You get better values from ACI 530 anyways.
Post-installed anchors have tested values like Hilti. Hilti has post installed bars for CMU. Why not use those tables?
Also, NCMA has a spreadsheet for cast in anchors:
http://ncma-br.org/pdfs/4/TEK12-03C-MSJC2013-Mason...
RE: Post Installed Anchorage to Masonry Wall
Yes, in my opinion. Interestingly, it's starting to creep into the literature as well. The Canadian concrete code commentary includes a very specific diagram of a shear wall on raft footing detail where they make much of taking the vertical hooks down below the mat rebar in acknowledgement of it being an anchorage situation rather than a development situation and trying to piece it together logically in strut and tie fashion. For what it's worth, pretty much nobody actually does take the hooks below the raft mat. Nor do they use strut and tie for the design, presumably because it would take forever.
The NEHRP seismic design guide on raft foundations also presents the same concern in one of its sidebars I believe.
As I see it, there are fundamentally two rebar situations:
1) You're passing rebar tension from one bar to another. This, fundamentally, is reinforced concrete design and requires development etc as usual.
2) You're passing rebar tension from rebar into concrete. This, fundamentally, is anchorage and usually ends up relying on some form of diagonal tension in the concrete.
The bars may not know but the concrete/CMU substrate certainly does. If you're the CMU and it's a case of #1, then you're just hanging back sipping Coronas and watching the tension pass you by. It it's #2, then you're working like a dog and straining every which way to move that tension out of the rebar in to a large enough portion of your body that the stresses are manageable.
Yes, welcome to the club where you will have lots and lots of company.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Post Installed Anchorage to Masonry Wall
The issue here is the checks for App D and ACI 530 anchors is about basically precluding a splitting failure on the substrate (concrete & CMU respectively) and, at least in the case of App D, are limited in their applicability. For example, App D doesn't really cover anything with embedments larger than 20*db (20*bar diameters). Hilti has some literature arguing that at embedments larger than 20*db splitting is precluded and you can look at post installed (or cast-in anchors I would argue) using development length "theory".
I like that visual... although I'd prefer some whiskey or Bud heavy over Corona. I see your point and agree. I guess I'm saying if you anchor laps a bar then you really are talking about your case #1. The tension from the anchor is passed from the anchor to the rebar much like a lap splice.