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

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

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

(OP)
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.





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

For option 3- is the assumption here that you're filling that cavity with concrete?

Have you considered an option similar to option 3- except with a full-thread adhesive anchor instead of your bolt/nut/washer stack; which is then filled with concrete (or grout or whatever) and then anchors are preloaded once the concrete is cured? This would give your concrete 'patch' a lot of confinement as well as place it in compression, potentially enough to cancel out all possible shear load being applied by screws coming in for the overhung jamb stud.

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

I would think bolting a stiffened channel or even just a 2x6 to the relatively flat concrete face would be more straight forward.

Is the slab mild steel reinforcement only? Any concerns with drilling the face? Evidence of spalling or other concrete loss? It appears to have two mats of reinforcement.

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

(OP)

Quote (jgKRI)

For option 3- is the assumption here that you're filling that cavity with concrete?

Not necessarily. I could ask for grouting but the intention is that the lateral load capability of the connection would no longer be dependent on the feasibility nor quality of that grouting. For what it's worth, vertical load carrying capacity here isn't much of an issue.

Quote (jgKRI)

Have you considered an option similar to option 3- except with a full-thread adhesive anchor instead of your bolt/nut/washer stack; which is then filled with concrete (or grout or whatever) and then anchors are preloaded once the concrete is cured?

Interesting. With options two and three, I'd been considering pre-load as a way to at least keep the grout in place. I'd not made the leap to then switching back to the original, top side fasteners under that scenario. Under that condition, I take it that you would be comfortable considering the outer fasteners as being as good as they would have been in monolithically cast concrete correctly placed? Specifying the preload strikes me as a bit tricky. Without meaningful stretch length etc, I doubt that I could reasonably expect much more than "torque wrench tight"

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

I lean more towards Option #2. I'd use a epoxy grout to fill that space (after roughening the existing concrete).....then install the bolt after it sets. Some pre-load in the bolt will help get it across via friction.

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

I think I like option 2, possibly substituting a couple of wedge anchors for the epoxy anchor.

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

(OP)

Quote (DTG)

I would think bolting a stiffened channel or even just a 2x6 to the relatively flat concrete face would be more straight forward.

You consider that relatively flat? Three issues that I have with a ledger option:

1) ledger will want to twist under load. that'll be a tensile force in the anchor and compression against the slab edge. I don't feel great about the compression given how rough the slab edge is.

2) amount of cantilever varies all over which would be a nightmare for coordinating the dimensions of the ledger piece.

3) it tends to detail out such that the top side fasteners either land pretty much at the gap between concrete and ledger or, in the case of a steel piece, at the heel which would be tough to fasten through.

Quote (DTG)

Is the slab mild steel reinforcement only? Any concerns with drilling the face? Evidence of spalling or other concrete loss? It appears to have two mats of reinforcement.

We believe this to be a mild slab but, yeah, some concern. We'll have to check it out. No slab edge live ends encountered yet. No evidence of spalling or other concrete loss. It's normal here to see two layers of slab reinforcement at slab edges. You'll have the chord bars running the perimeter. and some short hook bars up to the slab edge.

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

(OP)

Quote (WARose)

I lean more towards Option #2. I'd use a epoxy grout to fill that space (after roughening the existing concrete).....then install the bolt after it sets. Some pre-load in the bolt will help get it across via friction.

I do like the epoxy grout idea. Thanks.

Quote (HotRod)

I think I like option 2, possibly substituting a couple of wedge anchors for the epoxy anchor.

Is the wedge anchor preference just an economy thing?

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

Think I would agree with DTGT2002's approach.

My concern is when you go to PAF or screw down into your new 2" of grout/concrete patch there is a pretty good chance of splitting making that anchor useless again. with a channel or even a set of angles top and bottom you can PAF to the steel and handle the tensile loading from suction with an epoxy anchor into the slab with better cover and windward pressure gets picked up with bearing between the steel and edge of slab. Maybe in this approach to a skim coat of repair mix to just level the surface.

What is your intention with the angle you show on top of the plate, seems installing this would require you to cut the jamb studs and weld them on to get resistance for the windward pressure?



Edit: you replied to DTG as I was posting with some reasons to avoid that approach

Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering

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

A track + nested stud ledger will get you some more flexibility on the depth.



Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering

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

"Is the wedge anchor preference just an economy thing?"

There is that, but also, there have been failures of epoxy anchors due to creep under sustained tension, the most famous being some of the ceiling panels that came crashing down in Boston's "Big Dig" project several years ago.

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

Apparently, I glanced too quickly through the sketches and picture in the OP, and didn't realize there was a support surface below the slab. Knowing that, I like Celt83's second detail the best.

A possible improvement on it if the length of this repair is limited and access permits - use top and bottom pieces for the ledger that are slightly trapezoid shaped, and install them as overlapping wedges to provide some vertical precompression. Post-install the anchors after the ledger pieces are tightly wedged between the support surface below and the sill plate above.

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

Depending on the degree of exposure to the slab reinforcement, I think some grouting/skim coat would be prudent simply to ensure long term durability and corrosion protection. Aside from the connection strength considerations.

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

(OP)

Quote (Celt)

What is your intention with the angle you show on top of the plate, seems installing this would require you to cut the jamb studs and weld them on to get resistance for the windward pressure?

That is a whole other ball of wax. As I mentioned, the jamb studs are getting reinforced with a tiny, hot rolled channel. So I'll ultimately need to reach over from the angle bracket things to get that channel. Complexities include:

1) Tolerances in both horizontal directions.
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.

I left that bit out because a) hoping I can handle it myself and b) didn't want to make a long post even longer.

Quote (Celt)

A track + nested stud ledger will get you some more flexibility on the depth.

Better. Thanks for the sketch. My concern is still the range of possible stud cantilevers that I need to deal with. Even as you've shown it, I imagine that any cantilever less than about 1-1/2" is going to require another solution. The nature of this is that there are a few towers with, presumably, this problem all over. It'll onerous for everybody if we're having to come up with a custom solution every other week for the next six months. Although, perhaps I could manage with two solutions: yours + small can't relying on back edge PAF. I'll look into it.

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

(OP)

Quote (HR)

here is that, but also, there have been failures of epoxy anchors due to creep under sustained tension, the most famous being some of the ceiling panels that came crashing down in Boston's "Big Dig" project several years ago.

I don't consider this a sustained tension case really. Granted, there's always some wind. I'd expect the connection to spend 95% of it's life at load levels too low to worry about creep though. I'd have to investigate a little more but I had some concern for wedge anchors possibly putting wedge stresses into the patch material. That may well be avoidable with smart geometric detailing though.

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.

Quote (HR)

Apparently, I glanced too quickly through the sketches and picture in the OP, and didn't realize there was a support surface below the slab. Knowing that, I like Celt83's second detail the best
.

Noted. Those aren't bearing studs though right? Or, at least, they're not supposed to be. So technically no support in the vertical sense.

Quote (HR)

A possible improvement...

I might need a sketch to understand that. It sounds like a lot of parts on pieces for cant dimensions down to 1/2".

Quote (bones)

Depending on the degree of exposure to the slab reinforcement, I think some grouting/skim coat would be prudent simply to ensure long term durability and corrosion protection. Aside from the connection strength considerations.

Yeah, that becomes a tricky ethical question. Everything is inside the envelope and has been doing fine for forty years it seems. And my scope has technically been limited to just the work around these large wall penetrations. It has crossed my mind that, with a possible track-slab overlap as low as 1.625", there may be wall segments elsewhere in the structure that may not be fastened robustly even if demand is much lower. It would be pretty terrifying to be on the 30th floor on a windy day and have your living room wall tear off into the ether while you're watching football. Although, if you're a Packers fan, it's hard to imagine things getting much more dire than they already are.

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

What's the access/framing look like below? Easiest solution I see is abandon the anchor closest (or past) the slab edge, and through-bolt the inner fastener to the underside of the slab. If you have another jamb lining up below with the same connection, your through-bolt does double duty (might need generous slots to make that work), if not, provide a washer plate on the underside of the slab.

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

(OP)

Quote (CANPRO)

What's the access/framing look like below?

Same as above.

Quote (CANPRO)

Easiest solution I see is abandon the anchor closest (or past) the slab edge, and through-bolt the inner fastener to the underside of the slab.

Your overlap between the track and the slab is as little as 1.625" in spots. I don't see getting a through bolt in there and not having edge distance problems with the concrete. And possibly the track. Additionally, considering that the holes would need to be drilled near the interior face of a 3.625" stud cavity, I could see it being tough to get in there with a drill to get it done, particularly working at height.

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

Quote (KootK)

Interesting. With options two and three, I'd been considering pre-load as a way to at least keep the grout in place. I'd not made the leap to then switching back to the original, top side fasteners under that scenario. Under that condition, I take it that you would be comfortable considering the outer fasteners as being as good as they would have been in monolithically cast concrete correctly placed? Specifying the preload strikes me as a bit tricky. Without meaningful stretch length etc, I doubt that I could reasonably expect much more than "torque wrench tight"

Yes, my idea would be to go back to the original fasteners. You'd be basically filling that cavity, assuming that your jamb stud screws are transferring all their load into the new concrete. Any shear load at the interface between new/old concrete is aided by the rough interface and the confinement provided by the plate/anchor arrangement; any tension load at that interface is handled by the anchors, which should have enough preload to handle it. 1500lb is a very light load for a group of anchors even if they are relatively small; I would think you could hit that reliably, with a LOT of excess margin, without having to do any crazy field work.

Your face looks relatively rough already, and it would be easy to roughen further to get some increased engagement between old and new concrete if you feel it necessary.. The benefit I see with this solution is that it doesn't have to change at all based on the depth of the cantilever. You could even size the anchors for the longest possible cantilever, and just wind up with more anchor depth for any smaller cantilever; this means the guys doing the word can do the exact same thing every time, without having to worry about correctly placing different part numbers.

If you go to wedge anchors instead of adhesive anchors, your installation gets easier. You would form and place concrete, remove your formwork and drill for wedge anchors, install your backing plate and wedge anchors, preload your anchors, then install your jamb screws.

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

I imagine this idea could be rejected for a multitude of reasons, but hey it's an idea...

You could install a new wall on the interior and sister it to the existing wall framing. You can rest easy knowing the anchorage of the new wall will be dependable and the edge can be left alone as it has been for 40 years. Most, if not all of the work can be done from the interior and it would be standard, fast, relatively cheap construction. The tenants would lose that 4" of space though.

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

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.

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

"I might need a sketch to understand that."

Here you go; I hope it helps.
https://res.cloudinary.com/engineering-com/image/upload/v1543943022/tips/wedge_support_op68qi.pdf
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.

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

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.

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

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! thumbsup

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/

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

(OP)

Quote (jayrod)

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.

Quote (Celt)

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.



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

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.

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

(OP)

Quote (Once)

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.

Quote (Once)

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.

Quote (KootK)

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.

Quote (Once)

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.

Quote (KootK)

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.

Quote (Once)

How about a bent plate solution?

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

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

Quote (TehMightyEngineer)

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-a...

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-fasteners/screw-ancho...

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)

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

(OP)

Quote (Hotrod)

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.

Quote (jayrod)

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?

Quote (Hotrod)

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.

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

(OP)

Quote (TME)

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.

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

Quote (KootK)

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).

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

(OP)

Quote (TME)

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.

Quote (TME)

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

Quote (TEMRan some quick numbers on a typical wedge anchor.)


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.

Quote (TME)

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.

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

"...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.

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

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

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

Quote (KootK)

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.

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

Quote (jgKRI)

it's not impossible to get the nut on.

Been there; lesson learned.

Quote (KootK)

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? tongue We are rewarded by getting your advice in return; plus the free engineering education on various topics is more than worth it.

Quote (KootK)

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.

Quote (KootK)

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/

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

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/

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

Quote (KootK)


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.

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

Quote (Once)

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/

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

Pretty good for only 2 minutes!

Yeah, I had your detail rotated in my head. Seems like it could work but it cuts through the sills and the bent plate would have a high flexural demand to be stiff enough to transfer the load into the bolt. Obviously, only 1500 lbs but still enough to flex a small piece of metal like that.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://americanconcrete.com/

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

I like TME's setup with the notched angle. Looks like it would provide a solid connection to the stud.

If having it stick up above the floor is unacceptable, you could cut/grind out a slot in the concrete to recess the plate/angle leg, countersink the holes and use flat-head tap-cons (Might need more than 2, though) or drop-in expanding anchors like one of these and flat socket cap screws.

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

That's another way to accomplish the flush condition, kipfoot. Just have to make sure the concrete is chipped out to accommodate the fillet weld, or use a thicker angle and thread the hole (that requires a way to lock the threaded rod in place, such as high-strength threadlocker or a small tack weld on the top or bottom)

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

(OP)
Interesting development: apparently fire rating from the out side means that I can't have any connection plates projecting past the exterior face of stud. Botls and nuts ok I guess.

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

(OP)
1) I would like to thank everyone for their contributions on this. 'Twas a great help.

2) See below for the current solution. If anyone spots any issues, I would love to hear about them. You know, other than ridiculous cost.

You know when you develop a complex detail to solve an overly constrained problem and, at the end, you look back and say to yourslef yeah, that's just waaaay too much? This is that for me I'm afraid.







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

Yeah the welded arrangement makes that no fun.

Are you not comfortable with just running your original Kwik-Cons into the grout, hence the need to provide a different load path through the steel? (not saying you should be comfortable with that, you've done the math I'm sure).

6" x 3 1/2" angle is an off-the-shelf size. How about:

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

(OP)

Quote (jgKRI)

Are you not comfortable with just running your original Kwik-Cons into the grout, hence the need to provide a different load path through the steel?

That's right, I am not comfortable relying on the grout repair to serve as equivalent to original concrete from the perspective of anchor edge performance. To be frank, I didn't run any numbers on that. I don't actually know how to. It came down to just my visceral feel for whether not I could trust the patch to be stuck on there awesomely. In a way, I was kind of hoping that I'd come here and hear a whole bunch of "don't be silly, just count on the screws in the grout!". But, alas, I did not hear that. As a data point, can you tell me if you would be comfortable with just the original screws in the grout repair? Better still, do you know how to run the numbers on that?

Quote (jgKRI)

6" x 3 1/2" angle is an off-the-shelf size.

That is tempting. Here's what went into my decision not to do that:

1) I'd shift the angle down to miss the slab edge with the heel fillet. With the bolt remaining located where I put it, this would take my lever arm on the bolt down from 2" to 1". I could probably deal with that anchor wise or I could move the HUS anchor down a bit.

2) The 3.5" angle leg is only 1/8 shy of the inside face of the drywall. So not much tolerance for the depth of the concrete repair. Would it be the end of the world if the angle leg had to squish into the drywall a bit? Probably not.

3) I worry about accessibility and workers' ability to drill in this small cavity. Normally, when these kinds of clips etc are being installed, it's with no sheathing on either side which is obviously more forgiving. As qualitative antidotes to that:

- I set it up to eliminate the vertical screws between clip and bracket.
- I set it up to shift the horizontal screws further from the drywall than the would have been with off the shelf CFM hardware.
- I set it up so that, even if the column of screws closest to the drywall can't be installed, the numbers still work.

Thanks for the additional contribution jgKRI. I'm grateful to have it.

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

Quote (KootK)


That's right, I am not comfortable relying on the grout repair to serve as equivalent to original concrete from the perspective of anchor edge performance. To be frank, I didn't run any numbers on that. I don't actually know how to. It came down to just my visceral feel for whether not I could trust the patch to be stuck on there awesomely. In a way, I was kind of hoping that I'd come here and hear a whole bunch of "don't be silly, just count on the screws in the grout!". But, alas, I did not hear that. As a data point, can you tell me if you would be comfortable with just the original screws in the grout repair? Better still, do you know how to run the numbers on that?

I don't have enough experience in arrangements like this, or concrete in general, to trust my own intuition in this case. If I were in your shoes and having to solve this problem, I definitely do not think I would be comfortable treating any new grout as if it was equivalent to original, monolithic concrete, but my attitude when I get spooked is to go ultra-conservative so that applies here.

As far as a reliable/conservative calculation for this scenario? Man... I'd have no idea where to start. I apologize if the tone of my post came across as condescending at all- not my goal. This is a tricky situation and if you or any other known expert-level engineer had a solution, I was eager to learn it, hence my involvement in this thread when I'm actually out of my depth.

With that said... I don't see any other way to approach analyzing this thing other than to assume that all the forces ultimately resolve to tension in those horizontal concrete anchors... even the vertical load on the studs gets handled by bearing/friction at the grout/concrete joint, which is held together by tension in the anchor. But I digress.

Quote (KootK)

That is tempting. Here's what went into my decision not to do that:

1) I'd shift the angle down to miss the slab edge with the heel fillet. With the bolt remaining located where I put it, this would take my lever arm on the bolt down from 2" to 1". I could probably deal with that anchor wise or I could move the HUS anchor down a bit.

2) The 3.5" angle leg is only 1/8 shy of the inside face of the drywall. So not much tolerance for the depth of the concrete repair. Would it be the end of the world if the angle leg had to squish into the drywall a bit? Probably not.

3) I worry about accessibility and workers' ability to drill in this small cavity. Normally, when these kinds of clips etc are being installed, it's with no sheathing on either side which is obviously more forgiving. As qualitative antidotes to that:

- I set it up to eliminate the vertical screws between clip and bracket.
- I set it up to shift the horizontal screws further from the drywall than the would have been with off the shelf CFM hardware.
- I set it up so that, even if the column of screws closest to the drywall can't be installed, the numbers still work.

Thanks for the additional contribution jgKRI. I'm grateful to have it.

One major point I missed when reading your solution- your original constraints called for no field welding. When I saw welds in your sketches, I was confused- until just now when I realized that, duh, there's nothing preventing your arrangement from being welded before it's hung.

Also, access for placing the fasteners is a major problem, no doubt about that.

You're welcome, I hope my attempts to contribute aren't an annoyance to you and the other structural gurus on this forum- your threads often represent highly interesting thought problems, and it's fun and educational for me to try and keep up with the discussion. So, thank you for the effort you go through to explain your thought process and how you decide your approach.

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

If you haven’t already, double check with Sika about what grout product they recommend for this application. I believe Sikadur 31 is more like a thin adhesive gel than a grout.

Not sure if this is already your intention, but it would probably make the contractor’s life a lot easier if the plate assembly could be anchored first then do double duty as a grout form. In which case you’d be better off with a threaded anchor that can have a clamping nut on the back side of the plate. That would also give them the adjustability requires to get the plate perfectly flush with the stud, which might be tricky to do if they grout first and bolt a plate on after.

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

(OP)

Quote (jgKRI)

I apologize if the tone of my post came across as condescending at all- not my goal.

Quote (jgKRI)

I hope my attempts to contribute aren't an annoyance to you and the other structural gurus on this forum

Hell no. I didn't register your post as being condescending at all. I took your comments to be thoughtful challenges to the viability of my own solution. And that's exactly the kind of help that I need in order to vet this properly. Your latest proposal would be more economical than my solution in many respects. When I first saw it, I had to step back and revisit my assumptions in order to re-convince myself that I've been on the right path. And that's nothing but healthy.

With complicated details like this, two problems invariably plague my efforts:

1) I tend to fall irrevocably in love with my own ideas.

2) I resist revisiting my core starting assumptions because I've got so much invested in the solution currently tabled.

I only asked if you knew how to calc out the slab edge patch because I do not and I was truly hoping that you might. A hail Mary probing as it were.





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

(OP)

Quote (Bones)

Not sure if this is already your intention, but it would probably make the contractor’s life a lot easier if the plate assembly could be anchored first then do double duty as a grout form.

I agree that would be desirable but that is not my current intention. A few reasons for that:

1) With the grout gap being as little as 1/2" and rough, I wasn't confident that grout could be poured / packed in all instances.

2) As currently envisioned, we don't have top side access to this thing into which we would pour goop into the "form".

3) Having a nut, while great for adjust ability, make for more of an envelope protrusion.

This is merely my thinking to date. Your way may well be better, I don't know for certain.

Quote (Bones)

If you haven’t already, double check with Sika about what grout product they recommend for this application.

I did that as part of my detail development. They green lighted the epoxy. That said:

- They forced me to talk to a local sales guy rather than a tech svengali. I hate that.

- I stalked my local sales rep online. MBA, no formal training in engineering, and only with Sika nine months. Hopefully he is talking to the svengali behind the curtain.

- Sometimes I feel as though, in presenting my case, I wind up convincing these guys into agreeing with me rather than getting their best possible advice.

Your comments have had me wondering if Sika MonoTop 622 might be an acceptable, or even preferable, choice. It's non-epoxy and can be applied to vertical surfaces up to 2" without the need for forming. I wonder if it might be able to be shaved down after the fact as a poor man's version of tolerance mitigation. I'm guessing the epoxy grout might be too stiff for that.








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

Monotop 622 does look better suited for this... maybe the Sika reps have a good reason for suggesting Sikadur, but I dunno. It seems more like an adhesive than a grout.

There’s such a wide range of products, it’s hard to know which is best. I’ve specified Sikadur to be used with Combiflex joint membrane, which is a completely different application that what you’ve got going on. Maybe it can be modified somehow to be used as a thicker repair mortar? Might be worth asking a contractor if they’ve used it like that on other jobs.

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

I haven't used Sikadur yet, so I watched a few marketing videos from Sika about the Sikadur and now I would also agree with bones. I've used Sikatop 123 Plus; which I presume is somewhat similar to the Monotop 622 in general applicability. The Monotop seems like a repair mortar suitable for your needs. The Sikadur 31 looks more like an epoxy adhesive repair material for bonding two components together.

I'd use Sikadur 31 if I wanted to put pieces of concrete back onto the broken surface or was highly worried about bond strength. For your needs it seems like overkill.

Ian Riley, PE, SE
Professional Engineer (ME, NH, VT, CT, MA, FL) Structural Engineer (IL)
American Concrete Industries https://americanconcrete.com/

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

This thread popped into my head today..

Checking in, KootK- how did this repair work out? Did you wind up using your last-pitched idea to solve this?

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

Probably missed the party on this one, but something to be acutely aware of with Sikadur 32 is you need to put it on almost immediately prior to the concrete pour (there is a very small window). Often where you need it you cannot get access or have very poor access due to reinforcement, formwork, etc. But if you use it the bond of the two pours should make it more or less monolithic if the epoxy tie coat and the grout are applied correctly.

Additionally if I've learnt anything over the years, the contractor needs to get a licensed Sika applicator involved, and not try to attempt it themselves (instructions rarely followed otherwise, with understandably poor results).

EDIT - realised I meant sikadur 32 epoxy tie coat instead of sikadur 31... i'll go back to my hole now.

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

(OP)

Quote (jgKRI)

Checking in, KootK- how did this repair work out? Did you wind up using your last-pitched idea to solve this?

Well... I'm flattered by your continued interest in my little problem jgKRI. Thanks for that.

Yes, I did go with my last pitched idea. I'll post the final sketches below.

After seeing your latest post, I queried the contractor for some site photos which I was owed anyhow. I'll post those too.

The most interesting part of this ended up being the choice of Sika product for grouting. It unfolded like this:

1) I asked my Sika rep what product I should use and indicated that I was considering the Sikadur 31 epoxy system.

2) Sika rep said "we agree, Sikadur 31 will work for this applicaiton".

3) After some concept vetting here, I inquired again to the tune of "While I understand that Sikadur 31 would work, is that your recommendation for the best option for this application? Perhaps Sikatop 123 would be better?". That, per TME's input.

4) Sika rep said "yes, Sikatop 123 is our recommendation".

5) After a little research, I went to the contractor and said "hey, this Sikatop 123 might be a better choice than the Sikadur 31 that I originally specified. If you want to use it, I'm fine with it. The one caveat being that the Sikatop 123 requires a heating and hoarding period if temperatures will drop below freezing overnight. Even in December, an over night freeze in Vancouver is unlikely, but you never know".

6) The contractor, being rather adventurous, said "nah, I'm curious to try the Sikadur 31 anyhow and the hoarding may well be a problem. Let's stick with the Sikadur 31".

7) During the install, the contractor called and said "this stuff is very stiff and nearly impossible for me to work with. Can I switch to the Sikatop 123?".

So the correct answer here ended up being the Sikadur 123.



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

(OP)

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

(OP)


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

Hey, I'm a guy who always loves a little closure.

Thanks for the update. Looks like your solution worked out very well.

Interesting dialogue as far as working out which Sika product to use.

How well did the contractor take your proposal overall?

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

appreciate the follow up/closure....and wow that is one nasty looking slab edge in those photos it almost looks like a chunk spalled off during construction and was disposed of w/o any subsequent patching..odd.

Open Source Structural Applications: https://github.com/buddyd16/Structural-Engineering

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

(OP)

Quote (jgKRI)

How well did the contractor take your proposal overall?

It was hard to tell. There was no push back when we spoke on the phone but I was shielded by a few things:

- I was working sub to an envelope friend who did all of the PM work. So if there was bitching, he was surely the one hearing it.

- The contractor was a rather bold and adventurous fellow. He seemed entirely willing to put his head down and give it a go.

- The contractor was on the hook for just a single unit repair of a much larger complex. So the financial consequences were not dire. I suspect we'll be revisiting this once there's three high rises to deal with an most of the work being at height. Hopefully, the slab edge weirdness wasn't a persistent feature of the building.

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

Quote (KootK)

Hopefully, the slab edge weirdness wasn't a persistent feature of the building.

I think you just invited Mr. Murphy to the other 3 buildings.... wink

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