Anchor Bolt with full depth sleeve - epoxy grouted after installation

[rharting]

I'm working on the foundation design for various industrial storage tanks with some significant uplift/moments (some are 60' tall and about 12' in diameter) and a tall exhaust stack which is about 6' in diameter and over 100' tall. As you can imagine, uplift is a significant concern. The equipment manufacturer wants to use a pipe as a sleeve (full depth) to create a space to install an epoxy grout. In normal drilled epoxy grouted systems, the load path would go from the anchor rod to the grout and then from the grout to the concrete surface. In this instance, the load path would go from the anchor rod to the grout, from the grout to the pipe sleeve, and then from the pipe sleeve to the concrete. They want to do this for ease of installation (adjustability) however I have some concerns about whether this would meet ACI appendix D. I'm going to call Hilti, but I was wondering if anyone had any experience with this.

I looked into using the Deco adjustable anchor rods and while I think it's a neat solution, I have large concerns over where they got their numbers from. They have a chart which lists the "safe Load" (what engineer who knows anything about appendix D would list a safe load) and when I called and requested where they got the values, the very nice woman responded 'I'm not an engineer and we don't have an engineer on staff. However, those numbers did come from an engineer and that's about all I can tell you'. That's not good enough for me to specify your product when the loads are so large.

Any thoughts would be greatly appreciated.

 

[dik]

Have you looked into Wilson sleeves? There is also a corrugated plastic pocket that allows adjustment of anchor rods; the name escapes me. I've also used corrugated pipe with a bottom welded to one end, cast into concrete and filled with grout at a later time.

Dik

 

[rharting]

dik,
I have looked into Wilson, but they provide no loading information. I have felt uneasy using something that isn't approved by ACI or tested in accordance with 355. When you used the corrugated pipe (this sounds like the detail that they want to use), what is your assumed load path? With pretty good tensile forces, I want to make sure that I'm not going too far away from appendix D.

Thanks for your response.

 

[hokie66]

Why wouldn't you use a standard spiral metal grout tube? Just like in bonded post-tensioned construction. I wouldn't allow use of a straight wall pipe, or anything plastic.

 

[dik]

Hokie:
The metal is corrugated and has ridges that provide pull-out resistance, like a continuous 'keyway'; it's not a smooth wall. Grout tubes generally are too small to provide any latitude for placing anchor rods.

Load Path??? wazzat? The anchor rod pulls on the grout plug which is resisted by shear on the sidewall corrugations. The load is transferred into whatever the anchor rods are connected to. The resistance is calculated based on shear in concrete with a liberal safety factor. I'm not aware of any published data. Because of the larger diametre shear of the corrugations is not normally a big issue. The use of corrugated pipe allows a greater flexibility in placing anchor rods. The method was shown to me about 45 years ago...

 

[hokie66]

dik,
It think we are talking about essentially the same thing. I don't know how much adjustment the OP needs, but grout tubes come quite large, at least 130 mm I.D.

 

[Ingenuity]

Spiral seamed PT ducting comes in internal diameters from 2" to 9" diameter, with about 1/2" increments. Typically manufactured in 15'-20' lengths that are easily cut on site with an angle grinder, or equal. Used often for post-grouted applications, similar to what you describe.

Check out

http://www.dsiamerica.com/products/...ost-tensioning-system/installation/ducts.html

Re epoxy-based grouts: if the annular space between anchor and grouting sleeve is large, the exothermic heat due to the epoxy reaction may cause cracking of the resin. Extending the epoxy grout with a suitable sized dry aggregate will provide some heat-sink "mass" and also resin volume reduction.

In 1999 we did repairs to about 200 each anchor bolts to a 120' high chimney stack that was under construction where the anchor bolts pulled out at less than 10% of required capacity. Approx 5' long x 1.5" dia, straight-shaft bolts that were paint finished - hence the failure after concrete placement. We had to pull out all the bolts, remove paint and reinstall via a special technique, then load test. Nice repair job, but pissed off contractor having to spend $ on a repair during construction.