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Re: Post Tension Anchor Bolts

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Rich,

Check the "bolt in the can" detail" closely and any accompanying notes to see if they recommend filling the can with grout after post tensioning.  Sometimes they do and sometimes they don't.  If the can is not filled with grout then you are correct that it can only take tension.  It is common on large rotating equipment to resist the shear loads with either "shear lugs" on the bottom of the base plates or "stop posts".  Stop posts are typically imbedded vertical wide flange sections butted up against the machine base frame or in some cases they may even have adjustable set screws.  For seismic loads you are not allowed to use the friction from the machine DL.  Using the friction resistance from the clamping force is probably dubious since the concrete will continue to shrink and creep over time.  As far as bolt material, use what your loads dictate.  ASTM A36 is just fine and very ductile as long as the diameter required is reasonable.  There is no need to go for high strength bolt steel unless you need it by design.

Thomas Hunt, S.E.
ABS Consulting



"Rich Lewis" <sea(--nospam--at)lewisengineering.com>

01/04/2005 06:37 PM

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Post Tension Anchor Bolts





I have a project needing post tensioned anchor bolts.  I know this has been discussed in the past year but the Archive search doesn’t seem to do well on recent posts.  

 

I have a detail from the machine equipment supplier showing the bolt encased in a tube.  About 2/3 of the way down there is a plate for the anchor rod to thread into.  The plate is located in a “bulge” in the tube to anchor the plate.  The tube allows the anchor bolt to be tensioned free from the bond of the concrete.

 

My question has to do with the design of the anchor bolt for pullout.  It seems to me the anchor can only take tension, no shear, since it floats in the tube.  The shear must be taken by the friction of the post tensioning force clamping the base plate to the concrete.  So when I check the anchor for pullout base on ACI Appendix “D” I only need to check it for tension.

 

Am I evaluating this condition correctly?

 

Also, I see in the archives that ASTM A193, B7 is recommended for the anchor bolts.  Since this is an old post. Is this still the correct material?  I was considering the 95 ksi yield strength of this material.  

 

Thanks.

 

 
Rich Lewis
Lewis Engineering