Wet Setting Nelson Studs into Bond Beam 11

[KootK]

Got the situation below. I've pitched post installed anchors (Hilti HUS) for the fastening. There's a desire to use nelson studs but, presumably, those would be wet set. I'm concerned about the wet set nelson studs for these reasons:

1) Issues with wet setting anchors in general compromising capacity.

2) Not sure the grout will be well consolidated if there's a rush to get the channel on before it sets. Does bond beam grout get vibrated?

3) Contractor might not manage the sequencing and I'll be stuck detailing a post installed solution anyhow.

How do we feel about the viability of the nelson stud option?

 

[jayrod12]

I think the bigger load consideration is likely the out of plane loads from the masonry wall as opposed to the in-plane brace loads. I feel the column bearing on the wall transfers the bulk of the load anyway.

 

[dik]

Can you have, say 3" holes in the channel to put the grout in and let the air out?

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

-Dik

 

[KootK]

If the tolerance requirement are tight then embed anchor bolts by mason, steel plates bolted on top of the wall, then field weld channel to plates. A lot more steps but you can tighten the tolerance at each step.

Thanks GC I cycled through something similar.

Another option that I wouldn't mind would be studs on intermittent plates and then plug weld the channel to that. I could see the hole location coordination being a problem though.

Perhaps I just need to accept that level of tolerance as being managable.

 

[phamENG]

I'd avoid the wet setting, grouting through holes, etc. This is a lateral force resisting system connection and I presume it will be resisting seismic loads? Go with a readily inspect-able solution. I really like Celt's option, but I'd go with an oversized hole (think DG1 base plate anchor hole oversized hole) rather than a slot. That'll give adjust-ability through 360 degrees and some minor angle of tilt. Your original HUS screw anchor idea is just fine, too

 

[KootK]

Or just insist on the post installed anchors. Surely they can suffer an hour's labor of drilling.

It's not actually the contractor that's opposed to post install. It's the engineer. The channel was my idea as a substitution for an HSS that was causing install issues. The contractor has verified that they feel that they can to the erection with the Nelson studs if that's what the EOR wants. The engineer likes the nelson stud solution because they are familiar with it and it doesn't involve much rework on the design end at this point. The answer will be the nelson studs unless I'm able to develop convincing arguments for it to be something else. Frankly, my primary argument will be that I feel the odds of not being able to wet set the thing are high and that the engineer will wind up needing to to post install eventually anyhow.

 

[KootK]

This is a lateral force resisting system connection and I presume it will be resisting seismic loads?

Yes, ostensibly. Seismicity in Middle Earth Canada is pretty lame though so it's mostly wind & general stability.

I really like Celt's option, but I'd go with an oversized hole (think DG1 base plate anchor hole oversized hole) rather than a slot.

I like it too but, at the same time, it's more work than the screw anchors and, therefore, it has to have some advantage over the screw anchors to come in first. The only advantage that I can think of is capacity and I don't need that here.

 

[KootK]

I think the bigger load consideration is likely the out of plane loads from the masonry wall as opposed to the in-plane brace loads. I feel the column bearing on the wall transfers the bulk of the load anyway.

You're surely right for a certain range of loading and I know for a fact that there are other engineers kicking around that tell that same story. As you probably know, this setup usually comes with DBA starter dowels on the column. When I've looked at the numbers on that setup, I've run into the following:

1) Most of the load is delivered at the top of the block wall where masonry bearing can start to be an issue.

2) 100% of the frame shear has to live in the column for a spell, and usually gets there via the bending of a plate element.

 

[KootK]

Can you have, say 3" holes in the channel to put the grout in and let the air out?

You bet we can if the consensus is that is a smart thing to do.

 

[azcats]

Does the slightly oversized hole required for the HUS anchors bother you here if you go that route?

And the following isn't a good idea yet, but something that might be made into one...

What if you permanently embedded some sort of continuous template (narrow bar strip or something) to accurately space the bolts across the top of the wall? Top of template level w/ top of wall. My worry here would be enough space to vibrate around it.

 

[Aesur]

What about placing the channel but leaving a gap between the CMU and Channel, coming back and dry packing around the anchors and using face shells to finish off the dry packed bond beam? Other than that I am in agreement with leaving holes in the beam to grout/vibrate around anchors, if the beam needs the full strength, maybe you can weld plates over the holes after grouting.

 

[KootK]

For that arrangement, I'd probably lower the work point of the braces and block out the ends of the wall for the gussets. Lap the wall reinforcement with the gussets and weld.

That is pretty awesome mechanically. Perhaps the awesomest I've always had a bit of a bee in my bonnet when it comes to rebar as drag struts though. Primarily for sport, what do you think of these concerns:

1) I see much of the drag load getting dumped out of the bars and into the wall early on via bond stress. In compression, this is fine. In tension, I feel like it means that you have to essentially shear fail your wall progressively inwards before you ever get anything resembling a uniform transfer of shear force into your wall. In this respect, I kind of like a non-bond stress transfer mechanism and a copious area of steel cross section to use axially (less strain). I'll happily admit that the channel may well be worse in this regard if I get unlucky and engage only some of the front anchors first.

2) We'll be moving a fair bit of axial load into the bond beam longitudinal bars. If there's any drape in those bars, I'd expect them to attempt to straighten out and tear the bond beam off of the wall proper in the upwards direction. dold's cap beam thing would help with this but, in my particular situation, would be an aesthetic problem. I suppose that a double bond beam and drag bars lowered to 8" below the top would help with this some.

 

[KootK]

Does the slightly oversized hole required for the HUS anchors bother you here if you go that route?

It may indeed. How oversized do they need to be?

...if the beam needs the full strength, maybe you can weld plates over the holes after grouting.

It doesn't need to be full strength. Mostly stiffness governed. And I'd up the seize if if meant a more constructable solution.

What about placing the channel but leaving a gap between the CMU and Channel, coming back and dry packing around the anchors and using face shells to finish off the dry packed bond beam?

I'm not sure that I understand. Are you proposing a gap that would leave the nelson studs completely above the masonry prior to dry packing?

 

[azcats]

Looks like the fixture needs to be drilled at 1/8" larger than the nominal dimension of your anchor.

https://www.hilti.com/medias/sys_ma...chnical-information-ASSET-DOC-LOC-1543417.pdf

 

[Aesur]

@KootK - Yes, similar to if it was just another lift and they finish it off with face shells after dry packing.

 

[Agent666]

The way I've done this before is pour masonry say 2 blocks low but with rebar projecting, install steel, then pour the bit in between in concrete utilising letterbox shutters for placing concrete and vibrating (ensuring concrete in the letterbox chute goes above the steel channel web). Provide plenty of bleed holes in the web to ensure you can see the concrete coming right up to eliminate air voids (no different to grouting any baseplate/soleplate). Let it go off and remove the excess concrete from the chutes. If you really want to and steel section can handle it place regular holes to suit poking a small vibrator through the holes.

I don't like just dumping a whole lot of load into thin masonry, the shell is basically useless, and the core left over is very narrow for edge distances and so forth for anchors. Concrete is at least monolithic in this respect.

https://engineervsheep.com

 

[Agent666]

Additionally with the additional concrete width, you can have a small cage with 4 bars and closely spaced stirrups which goes some way towards alleviating some concrete breakout concerns for the parallel to edge case

https://engineervsheep.com

 

[XR250]

What are the loads, Koot?

 

[KootK]

I don't like just dumping a whole lot of load into thin masonry, the shell is basically useless, and the core left over is very narrow for edge distances and so forth for anchors. Concrete is at least monolithic in this respect.

That's a fine point, I feel the same. Thanks for chiming in to share your experience.

 

[KootK]

What are the loads, Koot?

I don't actually know. The engineer is doing the number crunching. I'll ask on Monday if I remember to.

 

[Deker]

1) I see much of the drag load getting dumped out of the bars and into the wall early on via bond stress. In compression, this is fine. In tension, I feel like it means that you have to essentially shear fail your wall progressively inwards before you ever get anything resembling a uniform transfer of shear force into your wall. In this respect, I kind of like a non-bond stress transfer mechanism and a copious area of steel cross section to use axially (less strain). I'll happily admit that the channel may well be worse in this regard if I get unlucky and engage only some of the front anchors first.

I think that's plausible, but if you lapped the drag bars with reinforcement that runs the full length of the wall I wouldn't lose sleep over it. You could also upsize the reinforcement to minimize axial strain like you mentioned. My thoughts on this are somewhat dependent on the magnitude of the load, which for this project doesn't appear to be large enough to make me second guess.

2) We'll be moving a fair bit of axial load into the bond beam longitudinal bars. If there's any drape in those bars, I'd expect them to attempt to straighten out and tear the bond beam off of the wall proper in the upwards direction. dold's cap beam thing would help with this but, in my particular situation, would be an aesthetic problem. I suppose that a double bond beam and drag bars lowered to 8" below the top would help with this some.

Hopefully there wouldn't be too much drape in a horizontal bar that is tied off at each vertical, but for this application I'd probably add a 180 degree hook at the top of the verts and turn it so that the hook straddles the horizontals.

The way I've done this before is pour masonry say 2 blocks low but with rebar projecting, install steel, then pour the bit in between in concrete utilising letterbox shutters for placing concrete and vibrating (ensuring concrete in the letterbox chute goes above the steel channel web). Provide plenty of bleed holes in the web to ensure you can see the concrete coming right up to eliminate air voids (no different to grouting any baseplate/soleplate). Let it go off and remove the excess concrete from the chutes. If you really want to and steel section can handle it place regular holes to suit poking a small vibrator through the holes.

Star for providing a much better description of what I tried to articulate in my first post.