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RE: Bent Clip Plates

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I researched crack propagation and repair for my M.S. Grinding to remove the
cracks is risky business if you don't get all of it from a fatigue
standpoint.  I don't know if the connection is subject to direct repetitive
loading, but even temperature changes in a frame will induce some cyclic
loading in the plate, and it doesn't take much over the lifetime of the
joint to propagate a crack.  Furthermore, the ends of the bend line are a
natural location of a lot of torsional stress.  You don't want to make it
the weak point unless the plate is quite over-designed.

If you do intend to grind it out, use a red dye penetrant to be sure all of
the crack is removed.  Also, I recommend peening the ground area, and most
of nearby bend line, with an impact chisel to offer some protection from any
re-initiation of any cracks not completely removed.  In the end its probably
in your best interest to have the fabricator correct the fabrication error
with a new piece than you trying to compensate for poor quality--that puts
liability on you.

____________________________________________
Paul J. Pilarski, EIT
600 108th Avenue NE
Tel: (425) 450-2592
Suite 400
Fax: (425) 453-9179
Bellevue, WA 98004
E-MAIL: ppilarski(--nospam--at)hntb.com







> -----Original Message-----
> From:	Canitz, Charles F NAB02 [SMTP:Charles.F.Canitz(--nospam--at)nab02.usace.army.mil]
> Sent:	Friday, April 21, 2000 7:42 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
>