High demand 3-5/8" jamb stud connection cantilevering 2" past rough slab edge.

[KootK]

This thread introduction may well be too long for busy folks to read. If so, you can probably get a pretty good jist of it just by scrolling through the graphics. I won't be lambasting anybody because they bring up something that I have already mentioned in the text.

I've presented some possible solutions below that I would like to have vetted by the gang. Naturally, I would also be utterly thrilled to entertain alternate, better solutions. In my heart of hearts, I'd like to rip out the walls and replace them with the 6" studs that should have been there to begin with. That would not be good client care in this instance however.

THE SITUATION

1) existing 3-5/8" jamb stud for a rather large wall opening in a highrise condo.

2) jamb stud will deliver about 1500 lbs ULS wind shear to its slab connection.

3) jamb stud is already being reinforced with a nested, 3" steel channel.

4) original connection design was some aggressively designed clips and concrete screws.

5) site work has revealed that, in some locations, the slab edge was originally saw cut as shown in the the photo below. Some kind of field error presumably.

6) my hardworking jamb stud connection now has a stud cantilever of up to 2".

7) expensive folks are standing around on site seeking direction.

THE CONSTRAINTS (AT LEAST FOR NOW)

8) Existing wall system is to remain in place during repair. Exterior sheathing will come off.

9) Need a solution that works for stud cantilevers ranging from 1/2" min to 2" max.

10) No field welding.

11) Need to be a little sensitive to building envelope concerns. I can, locally, have a bit of steel that would project into the exterior sheathing/insulation space.

THE OPTIONS CURRENTLY TABLED

OPTION 1. For a short length of slab, feather out the slab edge with repair concrete somehow. This would, ostensibly, be pretty great. Can that be done in such a way that we'd trust that repair concrete to be able to handle the fastener shear loads coming in from the jamb studs though? It gives me the heebee jeebess. I also worry that it's hard to do without removing the existing stud work. I would be interested to hear if this solution is viable and, if it is, recommendations for appropriate materials and procedures.

OPTION 2. This is a clever solution suggested by the client. My main concern with this is the viability of the grouting which would need to work at thicknesses ranging from 1/2" to 2". If the grout is installed before the bolt, will it just fall off during drill & epoxy'ing of the bolt? Would it be feasible to install the bolt first, grout around it, and then attach the angle? Could the bolt and angle be installed first, with the angle kept still somehow, and then grout be stuffed in behind the angle as a final operation?

OPTION 3. Similar to option two but no longer reliant on grouting feasibility. It's just... kinda silly looking. I would like to do something similar with a single back side nut, much like traffic sign structure bases are handled sometimes. Given the access situation, however, is there any way that I could use a single, backside not and be confident that it would be locked in place for the long haul? This would be easier at the 2" dimension and harder at the 1/2" dimension I reckon.

 

[Once20036]

Here's my four cents:

1) Any potential for a thin gauge clip on the inside? Something that would be hidden under room finishes (residential? Carpet?) at the completion of construction?

2) What't the facade on the building? Most of these solutions show a bolt head protruding past the oustide face of the newly extended slab edge. Is there any concern there?

3) Many of the above sketches are only addressing the condition at the base of the jamb. This is also a problem at the top of the studs, correct?

4) How about a bent plate solution? I`m envisioning showing up to the site with a bunch of pre-bent plates of various widths (L4x1/2, L4x1, L4x1-1/2, etc). These plates would be pre-drilled and anchored to the concrete (mechanical or epoxy) and self tapping screwed to your new hot rolled C reinforcing. There are some challenges there, but I think that concrete reinforcing/repair is minimized or eliminated. Maybe the cantilever is a red-herring and the L4x1/2 bent plate could be used everywhere.

 

[BridgeSmith]

"I might need a sketch to understand that."

Here you go; I hope it helps.
[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1543943022/tips/wedge_support_op68qi.pdf[/url]
Again, it may not be feasible or applicable to the conditions or needs of the project, but I thought I'd throw it out there.

Edit: It seems I may have misunderstood the loading conditions. If the loading is primarily lateral, my proposal here won't really be of much help. For that, probably a high-strength concrete patching material (HD-50), with wedge or epoxy anchors into the slab, is a good option. Adding a steel plate on the face would be even better.

 

[jayrod12]

I'm actually a fan of bones' suggestion if it's tolerable in the rom in question on all floors. Yes there is a loss of floor space, but damn if it isn't the easiest solution. Some flat plate light gauge clips from existing studs to new studs, jamb extensions on the windows and Bob's your uncle.

If the main concern, or you're being forced to limit your liability to the jamb studs only. How about providing a small pilaster on either side of the large opening so you can provide an angle clip connection on the inside face of the jamb studs. They furr out around the connection.

 

[TehMightyEngineer]

Ah, geez; I get too busy during my reply, refresh, and the thread gets 400% bigger. Now I have to start reading all over. Darn you for having really interesting but really lengthy topics!

I've done option #1 before in similar situations but only with positive connection crossing the cold-joint. Either with drilled and epoxied rebar or powder-actuated fasteners. I've done non-structural repairs of concrete without steel crossing the joint and between the contractors ignoring any bonding details (saturated surface, cleaning up dust and loose aggregate, etc.) and the lack of attention to curing; the repairs are not ideal for bonding to the existing and I would not have trusted them.

In short, I'd do option #1 only if forced to and would require continuous inspection of the process.

I agree with jgKRI's post entirely. A wedge anchor is going to be more cost-effective over epoxy anchorage and will install faster with less skill required on the installers part. I also agree that the existing surface looks fairly good for bond already; simply remove the loose bits, clean any dust, wet and skim coat, and epoxy grout.

I'd probably not use such a large steel plate, unless you really wanted to. I suspect you could utilize stainless steel plate washers and get sufficient bearing with those alone. The wedge anchors could also be stainless steel without too much expense and this should eliminate any corrosion concerns for the repair.

Ran some quick numbers on a typical wedge anchor. Looks like 3/8"Ø gets you there but 1/2"Ø would give you even more safety factor. Will need to make sure you have enough length though; often times wedge anchors have a set length and your embed might not be enough for the up to 2" of concrete. Perhaps a coupling nut embedded in the grout?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://americanconcrete.com/

 

[KootK]

I'm actually a fan of bones' suggestion if it's tolerable in the rom in question on all floors.

Me too. I bet it will get nixed but I'll put it on the table regardless. The contractor went nuts when I specified some Clark Dietrich stuff instead of Home Depot. I can't imagine that he's going to react too favorably to any of this heavy duty connection stuff.

If this is just for the horizontal forces is something like these a non-starter:

Something of that sort will be how I attache the angle clips to the channel reinforcing. It was how I was connecting to the concrete back when I had some.

Here's the original detailing back when I had slab edge. I didn't include it originally because I didn't want to over complicate things. Clearly, though, I'm just withholding meaningful context to smart folks who are working hard to help me.

 

[BridgeSmith]

TME's post jogged my memory on the other argument against epoxy anchors - commonly poor installation. After having the ends of bridge girders pop up in the middle of construction because the contractor "forget" to cast the tie-down anchor bolts in, and epoxied them instead, we only use epoxy anchors in shear only applications. If the holes don't get cleaned really well, the whole thing just pulls out, and if they don't get the 2 parts thoroughly mixed, it never sets up.

 

[KootK]

1) Any potential for a thin gauge clip on the inside? Something that would be hidden under room finishes (residential? Carpet?) at the completion of construction?

Thanks for your contribution here. Carpet & exposed ceiling. Some potential for this and I'll pitch it.

2) What't the facade on the building? Most of these solutions show a bolt head protruding past the oustide face of the newly extended slab edge. Is there any concern there?

Sexy stucco. And yes, your concern for envelope is on point. My direct client is actually a rockstar envelope firm that I do stuff with from time to time. Check out point #11 in my original post and the quote below which nobody has yet responded to. Part of the reason the client beat me to the punch on #2 is that I'd been previously trying exotic things to keep everything inside the sheathing plane.

Another concern that I have here is the projection of the bolt into the envelope. You'll have a plate and nut which are okay but what about the bolt projection? How short can one rely on that being without having to ask the contractor to cut them off? I'm not sure how big of a deal cutting them off would be. For this reason, I've been given some thought to using an internally threaded epoxy anchor. That, to hopefully facilitate a flush nut condition.

3) Many of the above sketches are only addressing the condition at the base of the jamb. This is also a problem at the top of the studs, correct?

Yup, per the quote below. Don't worry, I don't expect anybody to be keeping up with all this.

2) Need to deal with top of slab and bottom of slab connections simultaneously at many location.
3) Consideration of vertical slip at top which is made extra awkward by the fact that there is no allowance for that now.

How about a bent plate solution?

Not sure how this gets fastened into the concrete as the edge distance problem still exists, right?

 

[SwinnyGG]

Ran some quick numbers on a typical wedge anchor. Looks like 3/8"Ø gets you there but 1/2"Ø would give you even more safety factor. Will need to make sure you have enough length though; often times wedge anchors have a set length and your embed might not be enough for the up to 2" of concrete.

Hilti is the anchor manufacturer with whom I am most familiar. 1/2" Kwik-Bolt anchors are available in stainless steel in 6" (in 304 SS) and 5.5" (in 316 SS) lengths; design strength for these anchors are more than 2000 lbs each, with only 2 5/8" of embedment in 2500 psi concrete.

https://www.hilti.com/anchor-fasteners/expansion-anchors/r6282?CHA_ANCHOR_SIZE_LABEL_IMP=1/2 in

For a closer-to-flush head, you could use a screw anchor. 1/2" screw anchors are available @ 6", and have a design load of about 1500 lb per anchor with only 2 1/4" embedment in 2500 psi concrete.

https://www.hilti.com/anchor-fasten..._LENGTH=6 in&CHD_DRILL_BIT_DIAMETER_PM=1/2 in

My thinking on this is that you would not want any tension load applied in the new concrete- you'd want an appropriately sized hole all the way through the new placement, with all anchor tension applied into the existing slab, which means you'd have to over-drill the holes for screw anchors to a controlled depth; this might be a pain.

Wedge anchors are probably the cleanest overall solution, but you may wind up having to trim some of them after they are installed. If you use stainless anchors that's no big deal, with carbon steel anchors you're exposing the core so you have a corrosion concern to deal with.

Disclaimer- I don't work for Hilti, verify my numbers (obviously)

 

[KootK]

Edit: It seems I may have misunderstood the loading conditions. If the loading is primarily lateral, my proposal here won't really be of much help. For that, probably a high-strength concrete patching material (HD-50), with wedge or epoxy anchors into the slab, is a good option. Adding a steel plate on the face would be even better.

Thanks for the sketches, I recognize the effort that takes during a busy day. You get some serious creativity points. Yeah, right now, what you've proposed above is pretty much what I'll detail as my marquee solution. Everybody's convinced me to go with wedge anchors to I'll attempt that too unless envelope concerns steer me towards and internally threaded epoxy anchor.

How about providing a small pilaster on either side of the large opening so you can provide an angle clip connection on the inside face of the jamb studs. They furr out around the connection

I'll pitch it. Creativity points to you as well. Is you pilaster concrete, masonry, steel, or light gauge?

TME's post jogged my memory on the other argument against epoxy anchors...

Sold. The field personal may well not be versed in the installation of heavy duty anchors to begin with.

 

[KootK]

Darn you for having really interesting but really lengthy topics!

I've found that if I really focus on keeping my own threads moving, which is hard sometimes, I get a crazy amount of value/resolution out of them in a very short time. It's a huge help to a time conscious entrepreneur as you can imagine. And it's a testament to the willingness of our little gang to make selfless donations of the their time and creative energies. I've probably already received 4 HRS+ worth of free help from some highly paid folks this morning.

 

[SwinnyGG]

Another concern that I have here is the projection of the bolt into the envelope. You'll have a plate and nut which are okay but what about the bolt projection? How short can one rely on that being without having to ask the contractor to cut them off?

With wedge anchors, they almost always need to be hammered to get them in place; our typical practice is that the nut and washer go on the anchor BEFORE they are hammered in, so that when the stud inevitably peens a little during hammering, it's not impossible to get the nut on.

Holes are drilled a little deeper than needed, nuts are threaded on with one anchor thread proud, then the anchors are hammered in until the washer/nut are seated against the plate. You can control how much of the anchor is left sticking out with a decent level of consistency. You'll get another thread or two proud when you tension the anchors. If that's too much, it looks like in your installation it would be no problem as far as access to get a grinder in there and nip the heads off.

Your idea about an internally threaded anchor is worth exploring, but it seems to me that it would be difficult; you'd have to install the anchors and then somehow protect them while your grout/concrete is placed, or you'd have to put the fasteners in and hold the outer plate in place while you placed grout concrete- either way it's finicky.

To get flush heads with the internally threaded anchors, you'd also have to choose exact fastener lengths for every single position, so that you can tension your bolts without bottoming them out in the inserts (unless I'm misunderstanding something there).

 

[KootK]

I've done option #1 before in similar situations but only..

I gave some consideration to doing this with "Patch Pins" if you're familiar with those. Came to the conclusion that, in my heart, that's still just a cosmetic repair.

I'd probably not use such a large steel plate, unless you really wanted to.

Have you been considering the prying action in the connection? That will result in a fastener tension a good deal higher than 1500 lbs and really is what informed my choice of plate size. I've been trying to maximize the lever arm as you can imagine. I figure plate grout extent is a minor thing compared to trying to come up with a practical anchor design.

Perhaps a coupling nut embedded in the grout?

Clever, I'll keep that in my back pocket. It might give me an option for dealing with my "projecting bolt" problem. Just bring a bunch of precut bolt extension and install the one that makes sense for a particular geometry.

 

[BridgeSmith]

"...when the stud inevitably peens a little during hammering, it's not impossible to get the nut on."

In situations like that on my DIY projects, I generally thread the nut so the bolt is almost through the nut, and then hammer on the nut, so I don't mangle the threads at all.

 

[SwinnyGG]

Yeah. The hilti anchors actually have a little nub above the thread which is smaller than the thread D_p so that you can peen that part without ruining your ability to get the nut on.. but that doesn't always work.

 

[jayrod12]

I'll pitch it. Creativity points to you as well. Is you pilaster concrete, masonry, steel, or light gauge?

I was thinking light gauge, and just large enough to hide a angle or bent plate connection at the top and bottom of the jamb stud.

 

[TehMightyEngineer]

it's not impossible to get the nut on.

Been there; lesson learned.

I've probably already received 4 HRS+ worth of free help from some highly paid folks this morning.

What, you haven't been getting my invoices? We are rewarded by getting your advice in return; plus the free engineering education on various topics is more than worth it.

Have you been considering the prying action in the connection? That will result in a fastener tension a good deal higher than 1500 lbs and really is what informed my choice of plate size. I've been trying to maximize the lever arm as you can imagine. I figure plate grout extent is a minor thing compared to trying to come up with a practical anchor design.

I wasn't sure if your 1500 lbs included prying in it or not, so I used just the straight tension of 1500 lbs. I figured such details can be ironed out when you finalize your approach.

I would suspect you could eliminate most of the prying load by locating the wedge anchor 3" from the top of the slab.

Patch Pins

I haven't use them specifically but I looked into them a bit when you and I talked about them in a previous thread where you needed to get a composite topping to work without dedicated horizontal shear rebar. Seemed like a decent product.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://americanconcrete.com/

 

[TehMightyEngineer]

Kind of along the pilaster idea; we realistically only need to get tension back into the slab, right? The compression load from the stud could be transferred into the slab with option #1 easily enough.

Could you suffer a steel angle on the floor without messing up the finished floor elevation?

See attached. Might even get this to work for compression in the notched angle as well.

Edit: Reading more; maybe I'm unintentionally copying what jayrod is suggesting and I'm just skipping the pilaster?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://americanconcrete.com/

 

[Once20036]

How about a bent plate solution?
Not sure how this gets fastened into the concrete as the edge distance problem still exists, right?

I`m not sure how to post sketches, but I`m envisioning a bent plate aligned vertically.
The 4" leg would run parallel to the face of concrete and bolt into the face of concrete. The fastening to the concrete is a bolt, similar to your sketch #2.
The 1/2" leg would run along the stud. Fastening via self tapping screws - either through the bent pl into the stud, or better (?) through the stud into the bent pl.

This may have the added benefit of using one bolt into the slab edge to address both the jamb above and the jamb below (assuming they align)
These predrilled holes for the self tapping screws could be slotted to allow for your slip.

 

[TehMightyEngineer]

I`m not sure how to post sketches, but I`m envisioning a bent plate aligned vertically.

Like the attached? EDIT: Re-reading your post I've misunderstood your intent it appears. Do you think you can figure out how to post a sketch as it sounds interesting?

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries

https://americanconcrete.com/

 

[Once20036]

Attached?

I tried it by hand, but it was illegible. This is the 2 minute CAD version