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RE: Pinned Base Plate or Fixed

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There will be no formal statement, but that is the tendency from 
practitioners.  That said, the devil is in the details.  And most 
practitioners are not detailing moment connections to concrete very well. 
When we bolt steel to steel we always pretension the bolts.  And there are 
reasons for this.  When we detail steel to concrete the rationale should be 
 the same.  But not many practioners require tensioning anchor rods.  I owe 
 an article to MSC about this.  I have been remiss.

All that has to happen to convince anyone of the value is to model the 
detail.  The stretch of the anchor rods will shift the inflection point 
significantly and alter the stiffness of the modeled frame and alter the 
assumed drift.  Tension the anchor rods and the model will mimic the 
assumed behavior.

Tensioning anchor rods in the petrochemical world and in the projects on 
which I work is common.  But in the general "building" community, it is not 
 widely known.  When I first started tensioning anchor rods, there was a 
learning curve.  The first building in which I required tensioned anchor 
rods was in 1987.  I have required tensioning anchor rods from California 
to Alaska and even in some of my OCONUS work.

Regards, Harold Sprague

> From: behnamheydari_80(--nospam--at)
> Date: Thu, 19 Sep 2013 14:04:07 +0430
> Subject: RE: [SEAINT-SEAOSC] Pinned Base Plate or Fixed
> To: seaint-seaosc(--nospam--at)
> Harold,
> I checked the "AISC seismic provision". I found Fig. C-I-8.5.3,
> entitled: "Examples of rigid base plate assembly for MOMENT FRAMES". With
> this Figure, It seems that AISC tends to utilize fixed bse plate for 
> moment frames.
> Regards,
> Behnam

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