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RE: Stitch plate in double angles

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Thank you all for you insight.  I appreciate it very much.

The correct angles I show on my drawings are 3x3x3/8.  I caught the
error on the shop drawings, but, you guessed it, the angles were
fabricated and installed before the shop drawings made there way back to
the steel contractor.  Somebody sat on them a little too long, not me.

My options for the contractor are to weld additional cover plates to
strengthen the braces or replace them.

Thanks again.

Rich Lewis


-----Original Message-----
From: ASTANEH-ASL, Abolhassan, Professor, UC-Berkeley
[mailto:astaneh(--nospam--at)ce.berkeley.edu] 
Sent: Friday, February 25, 2005 10:43 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: Stitch plate in double angles, Re: seaint Digest for 24 Feb
2005
Importance: High

Dear Mr. Lewis: Since I have done a bit of research on double angles and

stitches ( my doctoral dissertation topic a few years back) I taught to 
have my 2-cents in if it helps.  In my opinion you are correct in all 
accounts in your e-mail. My suggestion to solve the problem would be to 
weld a continuous plate to the bottom of the double angle section (if 
existing stitches are not sticking out of the tip of angle legs) and
turn 
double angles to a kind of I-shape. Or, if stitches are sticking out,
weld 
two plates, or two smaller angles,  one inside each existing angle
,making 
the angles turn into closed shape triangular or rectangular boxes. You
need 
to check the new section for all failure modes such as overall buckling 
including flexural torsional buckling (specially if it is still open
shape) 
, segment buckling between the stitches, local buckling, stitch failure,

failure of connectors (welds or bolts) between the member and the gusset

plate (is this the end connection?) as well as connectors between the 
gusset plate and the rest of the structure.

If I were to weld  plates or angles to an  existing member, I would
check 
to see if the member has gravity load in it and what level of stress is 
there before heating it up by welding a new piece to it.  If stresses
are 
high, I would shore the members that are delivering gravity load to this

member and reduce or eliminate gravity stresses in it during the welding

process. Just to be prudent.
One last question: Is the thickness of  "one size smaller" angle less
than 
1/4" specified for 3x3x1/4"?

Finally, may be the best solution is to stick with your guns and do not 
accept this change.  Insist that they take the braces down and replace
them 
with correct members as specified. If they choose this route, they have
to 
make sure that removal and replacement of the wrong members are done
safely 
and do not create any residual stresses or strains that might affect the

structure in any adverse way.

Please notice that all of the above is only my opinion,  is for
information 
only, and does not necessarily reflect the views of my employer or the
file 
server Seaint where this is sent. If you choose to use any of the 
information in this e-mail,   you are totally and completely responsible

for all consequences of such use.
Best wishes.
Abolhassan Astaneh-Asl, Professor
Web: www.ce.berkeley.edu/~astaneh  and www.astaeh.net





    At 12:00 AM 2/25/2005 -0800, you wrote:
>From: "Lutz, James" <James.Lutz(--nospam--at)earthtech.com>
>To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
>Subject: RE: Stitch plate in double angles
>
>This message is in MIME format. Since your mail reader does not
understand
>this format, some or all of this message may not be legible.
>
>------_=_NextPart_001_01C51AC6.D1688764
>Content-Type: text/plain;
>         charset="iso-8859-1"
>
>Yup
>-----Original Message-----
>From: Rich Lewis [mailto:sea(--nospam--at)lewisengineering.com]
>Sent: Thursday, February 24, 2005 2:28 PM
>To: seaint(--nospam--at)seaint.org
>Subject: Stitch plate in double angles
>
>
>I designed a double angle knee brace.  The one supplied was one
thickness
>size smaller than the one I specified.  The brace has already been
erected.
>The contractor has asked me if he could add stitch plates to reduce the
>unbraced length so that the smaller on will work.  As I see it, the
stitch
>plate doesn't do anything for increasing the strength of this member.
The
>buckling strength of the double angles (3x3x1/4) based on the overall
length
>of the 2 angles together in the weak axis, not the individual angles
(page
>1-77 of AISC 9th ed.).  The stitch plates do not restrain the buckling
>behavior of the overall member.  It is still pinned at each end and
will
>buckle in a single mode shape about the weak axis.  I see stitch plates
as
>being spaced at whatever spacing is necessary to force the overall
member to
>buckle before an individual angle will buckle.
>
>Am I looking at this right?
>
>
>Rich Lewis
>
>
>
>
>This e-mail is intended to be delivered only to the named addressee(s)
and
>may contain information that is confidential and proprietary.  If this
>information is received by anyone other than the named addressee(s),
the
>recipient(s) should immediately notify the sender by e-mail and
promptly
>delete the transmitted material from your computer and server.  In no
event
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than
>the named addressee(s) without the express written consent of the
sender or
>the named addressee(s).
>


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