Post Installed Anchors Into Brick? 1

[Gopher13]

At least one post installed anchor manufacturer provides anchors that can be installed into existing brick. Has anyone used these before, and if so, what was the application and was it successful?

One example I can think of is fastening guardrail posts to the exterior of a building when a new mechanical unit is installed within the allowed distance to the edge of the roof. Does anyone agree with this, or should the brick not be relied upon for structural purposes?

Thanks in advance!

 

[BSVBD]

Please see attached...

The specifications i used are in the red boxes.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1485898021/tips/Brick_Hilti_013117_nvzybb.pdf[/url]

Here is a photo of the establishment. (Since you asked) The application is apparently successful as the canopies have been erected three years ago and are still where they were intended, through wind and snow. However... Use caution and discretion throughout inspecting the existing (hollow clay) brick, knowing the backer, how they are connected and making a final decision!!! These applications are more delicate than your standard steel beam.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1485898040/tips/Brick_Hilti_013117-2_khejos.pdf[/url]

Following is a more recent project. Notice the specification has changed slightly as Hilti has changed their product from HY20 to HY70 adhesive and all other applicable components.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1485898288/tips/Brick_Hilti_013117-3_zwsc5m.pdf[/url]

Hope this helps...

 

[bowlingdanish]

Well it obviously depends on the type of brick wall construction, its current condition, and what you intent to fix to it - so you will have to elaborate. But sure, things to post fixed to existing brick walls all the time.

 

[BSVBD]

Gopher... please forgive me for not thoroughly reading the second half of your post.

Regarding "fastening guardrail posts to the exterior of a building when a new mechanical unit is installed within the allowed distance to the edge of the roof.":

You've GOT to apply the intended imposed tensile force(s) as well as shear (if applicable) to your intended detail and determine whether the published Hilti data can support it. I'd be curious to see your intended detail on how you will fasten / anchor guardrails to the exterior face of brick for this specific application. Do you have a detail?

Now consider that you are supporting human life (since adjacent to roof top mechanical units, likely an accidental shock load from stumbling human) with these guardrails. Likewise, I was also designing to support steel structures to be supported above obvious human traffic. I was and always will be concerned and considerate. The end result of my decision was confidence after much investigation and research.

If the numbers work with your level of safety factor and confidence... proceed accordingly. My numbers worked and I did it.

If the numbers don't work... don't do it!

 

[Leftwow]

I've designed a project similar except it was a pipe support. If the brick has hollow spaces you have to fill the entire hole with the epoxy, make sure it is a slow hardening compound. Anchorage to brick is not as nearly as strong as concrete. We used Hilti post installed anchors. Like the HIT-HY 70 is says gel time is 4 minutes, after that you can't move it. We just used a standard A307 standard rod. But it looks like the guide does specify some screw anchors and cinch anchors as well. It's not cheap!

 

[cfox142]

Wouldn't you need to somehow check the brick tie in the motar joint unless the loads are very small and you can justify this by inspection? I have installed anchors into existing multi wythe brick walls before but the walls were over 1'-0" thick. I think Simpson has a load table for this.

 

[hokie66]

cfox is correct. The anchors are rarely the critical element, but rather the brick is. If the brick is a typical veneer, I shy away from using it as a structural element for anything other than minor gravity loading.

 

[dhengr]

Gopher13:
I agree with Cfox and Hokie, if there is any question, and you can’t prove it..., significant loads should be taken back to real structure that can be proven to carry it. Some vert. load can sometimes be borne by the brick veneer, assuming it is well supported from below. But, any concentrated lateral loads should be dealt with, with great caution, because the veneer tie-back to the structure is usually not designed for this. Sometimes, a standoff pipe can be employed. The bolts to the real structure fit through the pipe i.d., while the pipe improves the bearing area on the brick, but prevents the tightened bolt from pushing the brick veneer inward. This all has to be properly caulked and flashed.

 

[calvinandhobbes10]

Things I would potentially feel comfortable anchoring to brick alone: vertical fabric banner outriggers like you see in city streets, diagonal flagpole mount, rooftop antennae, etc. Not comfortable: anything carrying sustained load.

Your guardrail situation is a gray area (the load is code-mandated but not sustained). I imagine you want to face-mount it to the exterior of the parapet to avoid punching holes in the existing roofing. I've encountered this in the past. You're either Hilti HY-70 epoxying to the veneer, or through-bolting it through the veneer and backup too. Each post is extended downward with two mount plates spaced 1'-4" to 2'-8" apart to provide a resisting force couple. It's ugly, obviously. But it's cheap to install and tolerance-friendly. I'd take a look at what your back-up is. CMU--through-bolt, 1'-4" might do it. Metal studs--epoxy, but I'd go 2'-8" or so to keep the force couple really low.
HTH

 

[MotorCity]

I agree with others above......the brick assembly is the weakest link. If you have a force pushing toward the brick, the failure would most likely occur in the mortar joint. The force at which it fails depends of course on the span of the brick. Note that most brick ties don't work well (if at all) in compression so you cannot count on them as lateral "supports" for the brick, even if you are somehow able to locate them.

 

[Gopher13]

Thanks for the responses everyone! Great points made.

In my specific case, I have 4" brick + 8" cmu (no air space or insulation - circa 1940's, insulate with heat). I was planning on doing something similar to what calvinandhobbes mentioned with the two side mount plates spaced accordingly. I don't have to worry about the brick ties in compression as the brick would be pushing directly on the cmu, but for the tension side, I would somehow have to calculate the capacity of the brick trying to pull out of the wall at the anchorage point and perhaps bending of the brick?. I was trying to convince myself to just anchor to the brick but instead it sounds like the better way to do it would be to anchor through the brick and into the cmu?

Does everyone else punch through the roof and anchor to the existing structure? Design wise, this would be pretty easy but it seems like a roof leak waiting to happen.

 

[Ron]

I investigate design/construction defects and failures for a living. We often see brick ties that are either missing, improperly spaced or the wrong type of tie used for brick veneer. In short, the ties don't always get an opportunity to serve their intended purpose. When you add another load to that condition either in compression or tension, you risk the brick system taking all that load. As an example, your anchors would have to be immediately adjacent to the tie in order to take advantage of the tie capacity (which is limited to a few hundred pounds at best). Anything away from the tie loads the brick system itself.

Hanging canopies can have high loads transferred to the brick. Your condition is relatively open, so the lack of decking reduces both the wind loading and snow loading. Be sure that you caveat your design with appropriate notation to that effect so that subsequent uses that might consider a change to that condition would be appropriately warned.

Having said all that, I would anchor to the substrate, not the brick. I have designed over 50 hanging canopies in high wind and high snow load conditions. Each time we strived to isolate the brick from loading through a variety of means to take the loading back to the structural wall. Remember, by code in the US, the veneer is "non-structural" and is not considered to offer additional strength to the substrate.

 

[calvinandhobbes10]

Yes avoid potential roof leaks. This is a distinguishing service you are providing as a structural engineer, since many do not consider the other trades/failures. Roof leaks are way more likely than the types of failures being discussed here.
Your situation---I did this recently, same wall construction. I chose through-bolt over a deep HY-70 embedment (8" or so) that grabs both CMU/brick, because the CMU is almost certainly ungrouted. You might even find insulation stuffed in the cells.
Good luck.