Anchor Bolt Sleeves

[spats]

I wanted to see how other engineers feel about the use of anchor bolt/anchor rod sleeves. These are normally plastic sleeves that create an annular space around the top of a cast-in bolt to create a tolerance for adjustment by essentially bending the bolt. The sleeve is filled with non-shrink grout after adjustment. Supposedly they're used all the time, particularly for machinery and equipment foundations.

I just don't like the concept, but I'm willing to listen.

 

[hokie66]

I have used sleeves in industrial applications. We used steel pipe, not plastic. They do provide installation tolerance.

 

[SteveGregory]

Yep, I have seen soda pop bottles or cans used for machine anchor bolts.

 

[ATSE]

A secondary application is to create unbonded length where you want more tensile strain from your anchor bolts; say for a frame column anchor bolt group. An anchor bolt with 5" of unbonded length will provide 5x the ductility of a 1" long unbonded zone. Well, not really, since ductility is more complicated than that, but you get the idea.
This isn't common, but can be useful in seismic detailing or where inelastic excursions are expected.

 

[paddingtongreen]

It was used all the time in the oil refineries, towers with circular bases and bolts in a ring often needed a bolt location adjustment. It's a lot better than reaming out the holes for a misfit.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[ToadJones]

I have used them on machine bases.
The ones I used were made by the machine manufacture.
essentially a steel pipe with a circular hollow disc on the bottom that housed a plate washer and the bolt head. This allowed for the unit to be cast in place and allowed for a few inches of adjustment in every direction. Pretty slick.

 

[ToadJones]

ATSE-
I think i might be wrong here but I think Longer bolts do better for fatigue loading b/c of the % strain is less and the fatigue range goes down.
I think this might be the reason some machines use sleeves on the bolts.

 

[Lemony]

These are used in overturning moment resisting frames. They are used for constructability, and as ATSE said they get more stretch out of the bolt. They are addressed in AISC's Steel Design Guide 1 Base Plate and Anchor Rod Design, 2nd Edition and were included for the first time in ACI 318-11 Appendix D.

It is very important to address corrosion of exposed bolt with these.

 

[ToadJones]

I dont see these in DG 1

 

[Lemony]

It is touched upon in Appendix A. Not much information there, just design basis really.

 

[JoshPlumSE]

In my experience these are used because of constructability issues. If you've got a number of large diameter anchor rods and you're trying to set a large piece of equipment then you've got to do something to help. Either sleeve the bolts or use a larger bolt hole in your base plate.... which one is more acceptable from an engineering standpoint?

 

[JedClampett]

I don't work for these guys, but I like their product so much, I've been accused of that. This allows for adjustment without using a sledge hammer and as a bonus, the equipment can be slid over the base (no projections).

http://www.decomfg.com/media/deco-heavy-duty-adjustable-anchors-sales-sheets.pdf

 

[JoshPlumSE]

The problem that I've heard of with large embed plates (like the ones JedClampett is recommending) is that you run the risk of introducing air pockets underneath the plates. Therefore, you have to be careful with congestion and with vibrating the concrete down there.

That being said, those risks can be reduced. Therefore, it still looks like a decent and innovative product. If the cost isn't too high, then I'd think it could work nicely.

 

[JLNJ]

http://www.decomfg.com

if you are really serious about anchorage and flexibility for anchor locations.

 

[amec2004]

These are two main purposes for using anchor bolt sleeve

1. Provide a "stretch length" for pretension.
If the anchor bolt needs a pretension, it needs a free stretch length so that the pretension load will not lose with time being due to the relaxing of bond between anchor rod and concrete.

2. It allows bending anchor rod to fit in base plate hole if it's out of alignment, although it's not recommended.

We normally use the black electric tape to wrap the anchor rod on the sleeve portion and fill the sleeve with grout after pretension. In this way we can maintain the contact between anchor rod and concrete for bearing type shear transfer, and it also provides the "stretch length" by debond the wrapping bond stress between anchor rod and concrete.

You can go to

http://www.civilbay.com

to download the anchor bolt design software for anchor bolt design example as per ACI 318-08 Appendix D with both Anchor Reinforcement and Seismic Ductility provision. It will show you the recommended sleeve sizing and how the sleeve can help to achieve anchor bolt ductility design.

The "stretch length" for anchor bolt ductility has been codified in the new ACI 318-11 Appendix D.

 

[ToadJones]

amec2004-
Are you a contributor to the Civilbay website?

 

[hokie66]

amec2004,
What is the point of the tape? If you pretension the bolt before grouting, I see no reason to debond the bolt from the grout.

 

[amec2004]

hokie66,

To reply your inquiry, below is from ASCE " Wind Loads & Anchor Bolt Design for Petrochemical Facilities " section 4.3.4 Stretching Length on page 4-5

On a typical anchor bolt embedment, as a pre-load is placed upon the bolt, the bolt starts to shed its load to the concrete through its grip (bond) on the bolt. At that time, there exists a high bond stress at the first few inches of embedment. This bond will relieve itself over time and thereby reduce the pre-load on the bolt. Therefore, it is important that the bond be prevented on anchor bolts to be pre-tensioned. Bond on the bolt shaft can be prevented by wrapping the shaft with plastic tape or by heavily coating the bolt with grease immediately before placing concrete. Grout must not be allowed to bond to the anchor bolt. Tape the portion of the anchor bolt through the grout zone and to within one inch of the bolt head, below the sleeve ...

The bond between anchor rod and concrete is the unfavorable thing in anchor bolt design. Many engineers are surprised when they see the anchor rod is wrapped with black electric tape throughout the anchor rod all the way down to 2" above the head. It doesn't harm the anchorage at all, on the contrast, it gets the anchor bolt head engaged to the concrete right after applying tensile load, otherwise the anchor rod takes the load at top few inches and the head takes no load.

You can take a look at the ACI 318-08 Appendix D pullout resistance formula, it's just the anchor bolt head bearing, no bond stress along the anchor rod shaft.

I hope above will answer your inquiry.

The "stretch length" is recently codified in ACI 318-11 for ductile anchor design. I got a reply from the author of anchor bolt design software from

http://www.civilbay.com

and they say the "stretch length" will be updated in the ACI 318-11 version of anchor bolt design spreadsheet to reflect the anchor bolt ductility design for anchor bolt seismic application.

 

[hokie66]

I understand debonding the stretch length of the bolt, but your first post said that you apply the tape in the sleeved part, pretension, and then grout. If you have already pretensioned, why do you have concern about bond to the grout at that stage?

I wouldn't use electrical tape in that zone due to concerns about corrosion. It seems to me the smooth tape would allow a path for moisture accumulation. The cementitious grout provides much better corrosion protection in the absence of the tape. Below the sleeve, I can see the tape being used.

 

[amec2004]

hokie66,

I got your point.

For anchorages which require pre-tension there normally exist cyclic tensile load or dynamic impact load pattern. The cyclic load pattern causes the loading/unloading of tensile force on anchor bolt even after the grouting of sleeve. For this reason the debond is still required after grouting.

With regard to corrosion, it's always an issue for outdoor structures regardless of using tape or not. The anchor bolt design software from

http://www.civilbay.com

provide users an option of using 1/8" anchor rod diameter reduction, as corrosion allowance, with reduced Ase value in both tensile and shear resistance calculation. That's the normal practice to go.