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RE: WELDING: Inspection of Plug Welds in Primary Member Connections

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Bill,

Sorry for the delay but it appears that my email server is somewhat slow.  Bob
already pointed you to the relevant sections in AWS.  But I can tell you what
we've done for other similar projects.  I've worked on both the Central
Artery/Tunnel construction project in Boston and the BQE reconstruction project
in NYC.  They both have alot of steel boxes.  In all cases POT bearings are
being used, however the attachment of the POT bearing to the bottom flange is
accomplished in several ways:

1.   Directly welding in the field the bottom flange to the top plate of the POT
(yes this requires an overhand weld since the top plate is smaller than the
flange plate).

2.   Provide a shop-welded sole plate to the top plate of the POT.  Then either
     a.   Make sure the sole plate is larger than the bottom flange plate and
fillet weld the flange plate to sole plate (no overhand weld).
     b.   If the bottom flange plate is much larger than the top plate of the
POT bearing, just bolt the bottom flange plate to the sole plate which does not
have to be larger than the bottom flange plate, just large enough to allow for
bolting clearances and maintain minimum edge distances.

I may have details on the above if you want.

As to the "Stress Range" problem.  I wouldn't go that way.  First of all you
have to figure what stress category that detail is.  I don't think AASHTO shows
this detail anywhere.  Secondly, if it is allowed, the category will probably be
high 'E', which has an extremely small allowable.  As to the stresses in the
flange plate, I did some modelling one time on a bottom flange plate sitting on
a POT bearing.  Although the bearing stiffeners attract most of the vertical
load, you will get some localized tensile stresses in the bottom flange plate
due to bending as it bears on the POT bearing.  Unfortunately, I forget the
fraction of the vertical load which goes through the flange plate but it
probably varies based on the configuration.

Hope this helps.

Hector






"Bill Polhemus" <polhemus(--nospam--at)insync.net> on 10/14/99 02:04:17 PM

Please respond to seaint(--nospam--at)seaint.org

To:   seaint(--nospam--at)seaint.org
cc:    (bcc: Hector Morera/NYC/AmmannWhitney)
Fax to:
Subject:  RE: WELDING: Inspection of Plug Welds in Primary Member Connections




Thanks for the comments and observations.

> -----Original Message-----
> From: hmorera(--nospam--at)Ammann-Whitney.com [mailto:hmorera(--nospam--at)Ammann-Whitney.com]
> Sent: Thursday, October 14, 1999 12:39 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: WELDING: Inspection of Plug Welds in Primary Member
> Connections
>
> Out of curiosity, what are you using a plug weld for that
> can't accommodate a
> high strength bolt ?  We generally stay away from plug welds.

I will attempt to clarify.

We are using POT bearings at the supports for steel box girders. The bearing
sole plates which are to be field-welded to the bottom flange were
originally going to be fillet welded. However, in discussions with the DOT
folks, they mentioned that they have gone to using plug welds, with a hole
through the flange plate.

Now, it seems to me that such welds WILL experience "stress reversal" after
a fashion, but typically only in shear. "Stress range" is probably more to
the point.

In your opinion, then, this would be a problem?

* * *

> Do you need the sections from AWS D1.5 pertaining to plug
> welds?  There are only
> a few, I can send them to you if you want.  They don't appear
> to require any
> tests unless you deviate from the WPS provided.

I have the AWS D1.5. You might just point me to reference sections.

> -----Original Message-----
> From: Bob Shaw [mailto:rshaw(--nospam--at)steelstructures.com]
> Sent: Thursday, October 14, 1999 12:32 PM
> To: seaint(--nospam--at)seaint.org
> Subject: RE: WELDING: Inspection of Plug Welds in Primary Member
> Connections
>
>
> Keep in mind that plug and slot welds have very limited
> applications in
> D1.5. See 9.8(6), which prohibits plug and slot welds in
> members subject to
> tension and reversal of stress.