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RE: Bent Clip Plates

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Charlie,

The short answer for your question is no.

Several years ago, I worked for a telecommunications tower manufacturer.
The towers were constructed of 3 cold formed plate legs bent to 60 degrees
in a radius beyond the limits in AISC.  The thickness ranged from 3/8" to
1".   Cracks were not acceptable, and special rolled and cross rolled plates
were ordered from the mill.

Years before that, I worked for a structural steel fabricator / erector /
designer.  Frequently connectors were bent to form connections for beams at
a skew.  If the plate was bent in a break within the limits prescribed by
AISC, cracking was generally not a problem.  If there were surface cracks,
we generally found problems with the plate steel itself.  The carbon
contents were too high or other elements were present that reduced the steel
ductility.

The question now for your application is how was the depth of the crack
determined.  The best way is to cut, die, prepare surfaces, and use a 10
power loop to see the depth of the crack.  I have also looked at these
cracks with a scanning electron microscope.  The cracks were about 20 to 40
percent deeper than could be detected using die and a 10 power loop.  If the
cracks (as your reported) are visually 1/8" in depth, then you are cracked
more than 50% through the section.  

Surface grinding will just conceal the cracks.  Surface grinding will also
prevent die from penetrating.  I would require the connection plates to be
replaced. 

Regards,
Harold Sprague


> -----Original Message-----
> From:	Canitz, Charles F NAB02 [SMTP:Charles.F.Canitz(--nospam--at)nab02.usace.army.mil]
> Sent:	Friday, April 21, 2000 9:42 AM
> To:	'seaint(--nospam--at)seaint.org'
> Subject:	Bent Clip Plates
> 
> A contractor has requested(at the behest of the site inspector) that I
> inspect bent clip plates(used to transmit beam gravity loads) due to the
> presence of cracks at the outside corner(they radiate from the N.A. to the
> outside corner) of the bend. The cracks(two) also occur at the top and
> bottom edges of the bent corner of the plate. They are almost "surface"
> cracks in nature in that they are approximately 0.03 in wide and 1/8"
> deep.
> 
> The plate is 5/16" thick and 5 1/2" wide. The one outstanding leg is
> oriented approximately 120 degrees relative to the other. I've requested
> what bending radius was used and if the plate was bent parallel or
> perpendicular to its "roll".
> 
> Since the transmitted reactions are "light"(less than 4 kips), my
> recommendation is to surface grind to remove the cracks and install the
> plates. 
> 
> My question is are these type of cracks typical for bent plates?
> 
> 
> Thanks In Advance!
> 
> Charlie Canitz
>