Grout in oversized anchor holes instead of welding plate washer 1

[canwesteng]

Has anyone ever heard of this? Instead of welding a plate washer, just filling the hole with epoxy grout and then the plate washer sits on the oversize as it would anyway to transmit tension.

 

[phamENG]

No. It's unconfined. I doubt it could handle it. Might be worth a call to the grout manufacturer to see if they verify their product for that.

 

[dvd]

Seems like a bad idea from the standpoint of shortening the tensionable length of the anchor rod - from Chockfast anchor bolt literature

 

[canwesteng]

This is for building posts, not machines, so not concerned about the untensioned length. I heard someone else said they did this (well their firm did), and I want to know if it's a real solution. If it's reputable then I'd start using it but I don't see any references to this in AISC or anywhere.

 

[AskTooMuch]

Transfer tension or you mean shear?

Isn't welding washer to base plate with oversize holes used to transfer shear. Normal practice if washer is not welded to base plate is to only use half of the number bolts for shear. If you fill the oversize hole with epoxy grout, I'd say yes to can assume all the bolts transfer shear.

 

[canwesteng]

Yeah, grout used to transfer shear. The plate washer still transfers shear.

 

[AskTooMuch]

Weird way of doing it and maybe more expensive than just welding washer. I sbould say that would work because epoxy grout should have higher strength than concrete.

If you put shear key/plate it's bearing on concrete to transfer shear. Why can't you use same logic with epoxy grout which has higher strength to transmit shear from bolts.

 

[Tomfh]

Provided it’s quality epoxy and packed in tight it’s ok for modest shear loads, eg at a column base. Check the bearing strength of the epoxy over the plate thickness if you’re concerned.

 

[Smoulder]

Hilti has an option for this in Profis. I've never used the stuff but it's a Hilti product. Might have literature that states limitations.

 

[HTURKAK]

Yes. A special washer is used to fill the gap . In Germany you can find this type of washer (Verfuellscheiben)

https://www.mkt.de/fileadmin/mkt/pd...zelne Seiten/LP2022-23/Verfuellscheibe_VS.pdf

Pls look to your local market for HILTI dynamic set.

This subject allready discussed at threads ;

Large Through Bolt in Concrete Column for Support of a Bridge 2
thread507-488729

Hold down bolt design for Shear
thread507-500316

He is like a man building a house, who dug deep and laid the foundation on the rock. And when the flood arose, the stream beat vehemently against that house, and could not shake it, for it was founded on the rock..

Luke 6:48

 

[icebloom]

Filling of the annular gap between anchor and baseplate is noted in codes as one method of allowing shear forces to be equally shared between all anchors (failure crack starting at back anchors method). This is what the HILTI filling set Smoulder and HTURKAK reference does. If you look in the Eurocode EN1992-4 or fib 58 guide to concrete anchorage they state that high strength mortar can be used for a similar purpose (can't remember if its mentioned in ACI).

 

[human909]

For what it is worth. The welding of plate washers is generally not around these parts. (AS Code) We mostly just design the bolts for the shear and call it good. (I'm not going to argue that is 'RIGHT' just what is done.)

For serviceability the friction of tightened down baseplate is going to cover you 99% of the the time. At ULS you have the bearing of the bolt against the oversized baseplate hole which is going to have a stronger shear capacity than a welded washer putting the bolt into bending.

My 2c... I'd encourage people to strongly disagree with me on this one as I want to learn more.

 

[canwesteng]

Any column under uplift and shear has no friction... which covers any light framed steel structure with tension only bracing. I don't think at ULS you can necessarily accommodate the 1/2" of deflection at the base plate in a braced frame, likely all the load ends up being lumped at another column and loading those bolts to failure before this takes up the slack. Not saying this is true in every situation, and I'll do as you described often, anytime I feel the holes need not be especially oversized.

 

[human909]

Thanks for your response canwesteng. I'm deliberately being argumentative here and playing devils advocate to tease out the details.

Any column under uplift and shear has no friction... which covers any light framed steel structure with tension only bracing. I don't think at ULS you can necessarily accommodate the 1/2" of deflection at the base plate in a braced frame, likely all the load ends up being lumped at another column and loading those bolts to failure before this takes up the slack. Not saying this is true in every situation, and I'll do as you described often, anytime I feel the holes need not be especially oversized.

Isn't that why we ensure the bolts are tight? You still have compression between the base plate and the bearing surface even during uplife due to bolt tension. Designing for transfer via friction is certainly workable in many cases.

I'll do as you described often, anytime I feel the holes need not be especially oversized.

'We' here, and also I do it ever with oversized baseplate holes. This is especially true on light framed steel structures. I'm pretty sure this is the advocated approach by ASI our local equivalent of AISC.**

**After my above comment I figured I'd chase that comment further and buy the e-book (hard copy is at my office) of the ASI base plate design and actually look specifically at the design checks and basis. It relies on two of four bolts for shear at ULS. The general approach for shear comes straight out of an AISC Refence. Specifically, Base Plate and
Anchor Rod Design

So given that the AISC guidance accepts non welded plate washers, is this something that engineers are adding in unnecessarily? Or are people using 2 bolt connections rather than 4?

I'm just curious on why welding plate washers is so common in the US but not common in AUS. That is why I'm pulling this thread.

 

[dvd]

I do not understand the shear interface in this arrangement. Is the baseplate grouted with epoxy? Is there a plug of epoxy grout surrounding a cast-in-place anchor? Where is the reaction? Seems like the plug will either shear at the concrete/grout interface or shear at the grout/plate interface. If the oversized hole is per AISC, the area for grout shear is small, just a few square inches total. Depending on concrete shear strength and/or epoxy shear strength there does not seem to be parity with welded washers.

 

[Tomfh]

DVD, you fill the hole with epoxy grout, so that the bolt can’t move around in the hole.

 

[dvd]

Tomfh - how strong is it? Thus my question/statement.

 

[Tomfh]

Depends on the grout product and the geometry.

You have the epoxy grout acting in direct bearing within the hole, and shear as you noted.

 

[Eng16080]

canwesteng, This is mentioned as a "possible solution" in the book "Metal Building Systems" by Newman, 3rd edition. If you have it, refer to Section 13.8.3. There's a brief paragraph where it's written that the approach "seems reasonable and has been used in the past." Further, the author is not aware of any codes that "specifically allow or disallow this approach."