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Re: CJP Weld in a Moment Frame

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Chris,

Thank you for your answer.  You write: "but if you're trying to spreading the flange force over a larger area by adding a fillet, I don't think that's going happen."

That is exactly what I'm trying to do.  How can that not work?

Thanks,
MJ


--- On Fri, 2/26/10, Christopher Wright <chrisw(--nospam--at)skypoint.com> wrote:

> From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
> Subject: Re: CJP Weld in a Moment Frame
> To: seaint(--nospam--at)seaint.org
> Date: Friday, February 26, 2010, 10:43 AM
> 
> On Feb 26, 2010, at 11:32 AM, Mark Johnson wrote:
> 
> > Thanks for the reply.  I think what you gave me
> is a way to calculate the force in each flange if it were
> welded with fillets.  However, I have to take issue
> with several things:  (1) I'm starting with a CJP
> (complete joint penetration) weld at both flanges, (2) it
> matters what the beam is made of (A36 or A992 or other),
> i.e. Fy needs to be in your formula, (3) it matters what
> plate material your attaching to (A36 or other) i.e. Fy of
> the plate needs to be in your formula.
> Ordinary practice is that the base metal and the weld metal
> be 'matched' in strength. Typically the allowable weld
> stress is based on the weaker of the base metal and the weld
> metal. Sounds like your plate is weaker than the beam so
> you're trying to justify a build-up of weld metal to match
> the strength. If so you'll need the axial force in the
> flange to design the weld vis the formula given and then
> proportion the weld size by the ratio of the weld metal
> strength to the filler metal strength. I can't find anything
> like it in Blodgett, but that formula have have come from
> equating the force in the flange to the force in the weld
> and assuming that the base metal 'matched ' the filler
> metal.  If I were doing it, I'd certainly make sure I
> knew where that formula came from before I started plugging
> in numbers.
> 
> Just by equilibrium, the weld necessarily carries the same
> stress as the beam flange in a full penetration weld like I
> think you're describing, but if the plate allowable is less
> than the beam allowable you need to make allowances. Just a
> guess, but if you're trying to spreading the flange force
> over a larger area by adding a fillet, I don't think that's
> going happen.
> > 
> > My situation is that I have a W8x40 A992 beam welded
> to a 1.25" thick A36 plate with CJP welds at the
> flanges.  I maintain that doing this will NOT develop
> the beam.  (Yes, I want to 100% develop the
> beam).  I maintain that I need to add a fillet to the
> CJP (at least 5/16 fillet) in order to develop the moment
> capacity of the beam.
> Good practice is to use fillets with the kind of full
> penetration butt welds you're describing to reduce the
> potential for fatigue at the transition and make sure the
> necessary weld metal volume exists. It sounds like you also
> want some additional strength. You can figure the additional
> strength provided by the fillets in the usual way, again
> basing the weld allowable on the base metal (plate) strength
> rather than the strength of the filler metal.
> 
> I've never been particularly wild about just dumping in
> weld metal to build up a joint like this, although I admit
> I've been tempted a couple of times. There are a number of
> pitfalls including thermal distortion of the plate (and
> subsequent cracking when that distortion is too highly
> restrained) and tearing resulting from through-thickness
> loading on the plate. You might want to take a close look at
> how the plate itself might respond. Blodgett has some fairly
> simple approaches to this kind of connection in _Welded
> Structure Design_.
> 
> Christopher Wright P.E. |"They couldn't hit an elephant at
> chrisw(--nospam--at)skypoint.com   |
> this distance" (last words of Gen.
> .......................................| John Sedgwick,
> Spotsylvania 1864)
> http://www.skypoint.com/members/chrisw/
> 
> 
> 
> 
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