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Re: HILTI Anchor for anchoring Vessels

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Before I complied with the client's request, I would endeavor to introduce them to the available undercut mechanical anchors, such as those from Drillco Devices.
To your last question, I think you have both surface cracking and creep to address with the epoxy grouted rods, if you must maintain preload.  If mechanical undercut anchors are not permitted, you might be better off with a headed bolt in an oversize hole with a high-strength cementitious grout.
Mark D. Anderson
----- Original Message -----
Sent: Friday, March 17, 2006 6:58 AM
Subject: HILTI Anchor for anchoring Vessels

A client wants to set a vessel (8' dia X about 55' tall) on an existing, 2' thick, concrete mat, and anchor the vessel to the mat with 1" dia HILTI epoxy grouted anchor rods. The tension and shear in the bolt is 11000 lbs and 1000 lbs respectively. My scope of work is to determine the bolt embedment depth. I understand that the bolt will be pretensioned after the vessel is installed.

I used the published values of nominal bolt loads, adjustment factors for edge distance and bolt spacing etc. to calculate the bolt embedment depth.  One of the standard embedment lengths (12.375") is sufficient to support the vessel.

What bothers me is that the post-installed epoxy anchors are not approved by ACI 318 (See Appendix D for Scope of application) mainly because the reliability of these type of anchors has not been certified in accordance with ACI 355.2. However, the published bolt values in HILTI catalog have been certified, by  ICC Evaluation Service, to conform to UBC 1997, and 2000 IBC. The certification stipulates that it is valid only when the concrete is uncracked. The restriction stems from the fact that the anchors were not tested in cracked concrete environment.

The current thinking in anchor bolt design is that the headed bolt, or something similar, is the most effective anchor element. It is reported that L- shaped and J-shaped bolt perform poorly, in comparison. If L-shaped and J-shaped bolts perform poorly, how can a straight piece (despite having threads) perform any better?

Is it possible to pretension an, un-sleeved, anchor bolt? Is it not likely that concrete near the surface will crack?

Please share your thoughts and experiences, if any.



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