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Re: HILTI Anchor for anchoring Vessels

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I see that Neil Moore already answered the first of your questions.

Question 2 is from my own personal experience (not with HILTI).

Epoxied bolts are somewhat similar to cast in place rebar. The stress distribution is not equal along the length of the bar along the deformations. A headed anchor rod or undercut anchor has a fixed length to the point of resistance (the anchored head). The epoxied anchor will not diminish the ultimate tension strength, but the pretension load diminishes with creep and shrinkage. Another issue is heat. Epoxies will relax with time and temperature and this will also cause a loss in the initial pretensioned force.

Detailing can be performed to accomodate for some of the loss, but it is not definitive.

You can pretension the epoxied anchors, but you will have losses.

Regards,
Harold Sprague





From: Padmanabhan Rajendran <rakamaka(--nospam--at)yahoo.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: seaint(--nospam--at)seaint.org
Subject: Re: HILTI Anchor for anchoring Vessels
Date: Fri, 17 Mar 2006 12:41:48 -0800 (PST)

Harold,

Thanks.

1. I did not see any tables and charts to design Covert, Undercut anchor at their web site. Does it mean that I prescribe the loads and the Company designs on a case by case basis?

2. Hilti recommends tensioning epoxy anchors. So, what may be your objections to it?

Rajendran

Harold Sprague <spraguehope(--nospam--at)hotmail.com> wrote: I have used a Covert "Ductile Undercut Anchor" post installed mechanical
anchor rod and tensioned the anchor rods after installation.
http://www.covertoperationsinc.com/duc.html
On the applications that I have employed, the bolts were checked after a
week and showed no relaxation.

I would advise against tensioning an epoxy anchor.

Regards,
Harold Sprague

>
>   ----- Original Message -----
>   From: Padmanabhan Rajendran
>   To: seaint(--nospam--at)seaint.org
>   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.
>
>   Thanks.
>
>   Rajendran
>
>
>------------------------------------------------------------------------------
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