3/8" Plate Design 5

[MaxMedic]

I am trying to figure out if the 3/8" plate can handle the moment and deflection from the weight of the brick on the angle that is welded to the plate. I do not know how to approach this.

The plate and bolts are spaced at 16", I already have factored the spacing into the loading from the brick.

 

[phamENG]

RanVeer - that may serve to reduce the elastic deflection, but you still have the moment being resisted by a 3/8" plate.

 

[Veer007]

Thanks for the response. I'm not sure, can't we increase the plate thick to arrest moment? just a doubt

Thanks in advance!!

 

[JoelTXCive]

 

[Italo01]

This thread reminds me of a story my boss told me in my first engineering job in 1955.

BAretired, did you started as engineer in 1955 or it was a typo?

How can you remember all this details of a job?

Really amazing.

 

[HTURKAK]

IMO, the bracket height should be the same with slab thickness . The use of L8X4X(7/16) will create cold bridge and thermal problems. More over , the plate 3 X 3/8 in. magnify the deflection.

I will suggest to develop similar detail with HK5 - W at the following doc.

https://www.halfen.com/PDF-Dateien/...che Produktinformationen/FM_HALFEN_20-1_E.pdf

 

[BAretired]

BAretired, did you started as engineer in 1955 or it was a typo?

How can you remember all this details of a job?

Really amazing.

Not a typo. I graduated in 1955; got a job same year.
I don't remember many things, but that story impressed me. My boss told it better than I did.
Not so amazing. Nowadays, I can't remember what I ate for breakfast.

BA

 

[dik]

I don't like using expansion anchors close to the edge of anything. Epoxy OK.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[Veer007]

We don't use epoxy anchors at overhead locations, right?

Thanks in advance!!

 

[phamENG]

It can be done, but there are very strict requirements. The material needs to be properly certified, the installer has to have gone through the proper training, it must be continuously observed, etc.

In this case it's not under constant tension so some of those requirements can be relaxed.

 

[KootK]

It seems to me that the underside anchors are, in fact, in permanent tension (as well as permanent shear). I still like the screw anchor option that I showed earlier for the underside anchor if the numbers would work and this is the scheme OP wants to run with.

 

[phamENG]

KootK - I suppose you're right. But I'd be less worried about it as long as the anchor into the side of the slab is sized to take all of the tension in the connection. So long as the connection fit-up is nice and tight, that should be the stiffer load path to counteract the prying. The only time that anchor is really needed is wind suction pressure pulling the veneer away from the wall, but that would be resisted by the veneer ties in the backup and not the lintel and it's crazy hanger.

 

[dik]

Think of the "Big Dig"... with care they can easily be used. Your loads, albeit dead loads, are pretty small. I should have added, "guess what anchor is going to be taking nearly all the load."

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

The only time that anchor is really needed is wind suction pressure pulling the veneer away from the wall, but that would be resisted by the veneer ties in the backup and not the lintel and it's crazy hanger.

I would say that the "need" is captured by your first statement below.

RanVeer - that may serve to reduce the elastic deflection, but you still have the moment being resisted by a 3/8" plate.

So long as the connection fit-up is nice and tight, that should be the stiffer load path to counteract the prying.

I disagree. The main goal of the extra angle is to stiffen up the system by, effectively, shortening the hanging cantilever. Once that's done, the angle becomes the stiffer path until it fails.

I'd happy to say that underside adhesive anchors are probably okay here simply because it's just not that critical of an application. That's different from there being no permanent anchor tension however. As long as there's gravity on the system and no parts of the system have failed, I'd say that the underside anchors are experiencing tension.

 

[dold]

Think of the "Big Dig"

https://www.ntsb.gov/investigations/AccidentReports/Reports/HAR0702.pdf]

https://web.archive.org/web/2022020...tigations/AccidentReports/Reports/HAR0702.pdf

[/url]
^^ NTSB report on the incident. If I'm not mistaken, this was a catalyst for the increased scrutiny/regulation/special inspection requirements/etc etc for adhesive anchors that we see today.

---

To OP's question: Unless I missed it - is this slab already cast? If not, I'd just cast in an angle with headed studs at x" o.c. and weld a hanger (not a plate) - HSS, C, maybe a L?

Our office standard for steel framed buildings is shown below. Below below is an adaptation for concrete frame - which is totally half baked and kinda sucks if i'm honest. Essentially the whole concept is to give the maximum amount of adjustment once the building is all plumbed up and dead loaded.

But it looks like OP's condition doesnt have an exterior/bypass envelope? So these might not work at all.

Yea yea yea...this is a ton of steel I know I know. I don't write the rules. But the big-time all-in-one steel fab/erectors like this better than having to go back and cut a bunch of welds when the brick starts to get wonky.

 

[phamENG]

the angle becomes the stiffer path until it fails.

I agree, but I disagree with what I take to be your next step in the load path. If we remove the vertical anchor altogether, what happens? The system is still theoretically stable, and the angle still contributes to the load path.

 

[KootK]

If we remove the vertical anchor altogether, what happens?

I would say that what happens when the bolt is removed is that the prying mechanism that would otherwise have been present in the horizontal angle leg gets eliminated. In my mind, that represents a loss of stiffness because, kind of by definition, load paths involving prying tend to be stiffer than those not involving prying. And that brings me back to my contention that the load path that would put the anchor in permanent tension is the stiffer of the two load paths being discussed.

It may not even be all that prudent to assume that the direct tension load goes predominantly into the anchor installed into the slab edge. That, because:

1) The only way to install the thing snuggly, I think, would be to tighten the underside anchor first, pre-stressing the connection a bit.

2) Tightening the underside anchor first means that the slab edge anchor will inevitably have to move a bit before taking up the slop in the bolt hole and engaging the slab edge anchor in shear.

3) 1+2 = the tension likely starts off in the underside anchor.

 

[phamENG]

Fair points. With that sequence, you are - of course - correct. And another issue we probably haven't considered with this idea: unless we want to introduce the torsional stiffness of the angle into this we have to consider that the anchor in the underside angle needs to align with the hanger. If that's the case, we have a conflict with the horizontal anchor...

All in all I still very much dislike this detail.

 

[BAretired]

Yes, it is a terrible detail.

BA

 

[Brad805]

There are companies that make products for these problems. The one below is in the UK, but there must be someone in the US. A 9" thick slab would not be overly difficult to core thru for a small thru bolt if permissible.

 

[dik]

@dold... the 'Big Dig' failure occurred because the wrong type of adhesive was used. It was different than that spec'd and had a serious 'creep' problem. Within a couple of weeks of it happening, we had our local Hilti rep by expounding the merits of using adhesives. He was surprised that we were 'up' on the Boston 'Big Dig'. I'd sent a technical memo through the structural dept about a week earlier... just as a 'heads up' to that type of problem. With most stuff in engineering, you have to have a pretty good grasp of the properties of materials.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik