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RE: Anchor Bolt Design for Vessel/Stack

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Bill,
I have worked on this for quite a long time.  I have tensioned anchor rods 
back when they were anchor BOLTS.  Many other industries have tensioned 
anchor rods for a long time.  There are a lot of other considerations that 
you will need to factor.  There is also loss in tension that reduce the 
tension with time.  There is the issue of breaking the bond with the 
concrete.  If you don't, you will not have a reliable tensile force.  There 
 is also the method of how you measure the tensile force.

Every industry does it a bit differently.  The wind turbine industry has 
been using load indicating washers that are calibrated for a particular 
tension.  The nuclear industry uses calibrated hydraulic bolt tensioners. 
I prefer to use calibrated hydraulic bolt tensioners.  I have used this on 
projects from Louisiana to Alaska.  Millwrights are accustomed to using 
hydraulic bolt tensioners.  Riggers are also.  Iron workers need to talk to 
 the riggers.  But I have used this for buildings and all kinds of 
applications.

The first time was in 1976 when I had a tank that vibrated a lot in spite 
of my best calculations.  An iron worker buddy offered a "fix" when he put 
a cheater bar on a spud wrench and "stretched" the anchor bolts.  The 
vibration immediately stopped, and the light bulb went on above my head.

The ACI 318 is still applicable although the ductility requirements may be 
moot since with appropriate tensioning there will never be a net change in 
the stress in the anchor rod.

The applied tension of 70% of Fu is a bit generous for anchor rods.  It is 
appropriate for high strength bolts because there will be no relaxation 
because steel is totally elastic.  Concrete is less so because it needs to 
age.

One of your thoughts may require a bit of a paradigm shift.  This one is 
not very intuitive.  The force at the base does not change with applied 
tension until the the applied tension is greater than the pre-tension.  The 
 concept is the same as any steel to steel connection that is in tension. 
Steel to steel connections that are bolted with bolts in tension are 
required to tension bolts to 70% Fu.  When external loads are applied, the 
force in the anchor rod and the force at the anchor point does not change 
until the pretension force is exceeded.  Therefore your statement "Anchor 
steel strength would also be calculated using total force (pretension + 
tension from lateral loads)."  is not accurate.

It has been my intention to publish an article about this for a while.

Regards, Harold Sprague

> From: bill(--nospam--at)polhemus.cc
> Date: Tue, 19 Mar 2013 15:08:59 -0500
> Subject: [SEAINT-SEAOSC] Anchor Bolt Design for Vessel/Stack
> To: seaint-seaosc(--nospam--at)mail-list.com
> 
> Been awhile since I looked at this topic, and especially not in light of
> ACI 318 App. D.
> 
> Observations:
> 
> 1. Pretensioning bolts is a good idea. The benefits include lessening the
> possibility of bolt loosening and fatigue, and creating a sort of 
> composite behavior between the concrete foundation and the anchor bolts. 
> This is commonly done for anchoring tall slender structures such as 
> highway light standards.
> 
> 2. If pretension is sufficiently applied, the base ring will be in
> continual compression against the concrete (or grout).
> 
> 3. Pretension to 70% of Fu appears ideal for this purpose.

Truncated 1225 characters in the previous message to save energy.

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