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Re: ACI 355.2

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In a message dated 3/20/01 7:15:30 AM, MarkKGilligan(--nospam--at)compuserve.com writes:

<< I have received input from John Silva of Hilti and Richard Klingner who is 
on the committee that wrote ACI 355.2 and I have some comments on several 
related topics.>>

>I am disappointed to hear that some of this discussion has become private.  
I would have liked to have seen their comments in this forum.



<<I would be interested in specific reasons why the test procedure is

believed to be not reflective of field conditions.

> One item I see in 355.2 is that the test member is split to form a crack 
with a constant width (up to .020") for the full depth of the member.  
However, members in bending have cracks that open the widest at the tensile 
surface, and then reduce to zero somewhere within the depth of the member 
when heading towards the compression zone. Unfortunately, every single member 
that has different loading, size, steel content, etc. will develop a 
different shaped crack.  Complicated.  However, with the proper embedment, 
the crack width at the location of the clip of a wedge anchor may be zero.


<<During earthquakes we will often see

loads on the concrete in excess of those used in design.  In addition the 
loads on the anchors during an earthquake may be considerably larger than 
assumed.  

> And yet we allow a 1/3 increase on the strength of materials for ASD.

<<These realities combined with the relatively infrequent

occurrence of earthquakes, and thus limited experience with anchors in

these situations, argues that we should not ignore the impact of cracks on

anchor capacity when dealing with earthquake loading.

> The 1997 UBC and 2000 IBC Strength Design provisions for anchors in 
concrete require a 50% increase in the factored loads for anchors is tension 
zones.  ICBO ES could easily change their safety factors for allowable load 
tables for cracked concrete.  


<<A number of people have expressed concern about hearing of this problem at

the "last moment".  It should be noted that there was aa Aug 28,2000

posting to this list by Kent Carlson in  which he summarized the issues.

>  At that time, Kent asked the some 15,000 members (I think that is the 
number I read somewhere) of this list to indicate if they had ever had a 
problem with anchors in cracked concrete.  Zero replies.

Howard Silverman




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