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RE: CJP Weld in a Moment Frame

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I'm not sure if I understand what you are doing.  Are you welding the beam to the face of the plate like an extended end plate moment connection?  I just recently did a wale splice using a plate at the splice since the beam changed direction at the splice.  I wanted to develop the capacity of the beam using only fillet welds so I added a bar to the inner and outer flanges to increase the section modulus of the section at the splice and thus lower the stresses on the  welds, enabling me to use fillets.

Bob Garner, S.E.

-----Original Message-----
From: Richard Calvert [mailto:RichardC(--nospam--at)lbbe.com] 
Sent: Friday, February 26, 2010 10:26 AM
To: seaint(--nospam--at)seaint.org
Subject: RE: CJP Weld in a Moment Frame


P.S. Again, this is a fairly complicated approach, thus I recommend RBS joints - forcing the beam to be the failure mode, ensuring a ductile failure.  Much simpler.  

-----Original Message-----
From: Richard Calvert [mailto:RichardC(--nospam--at)lbbe.com] 
Sent: Friday, February 26, 2010 12:57 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: CJP Weld in a Moment Frame


-The weld formula holds for a CJP (this is why it is t_f*16 instead of just t in 16ths)
-The grade (Fy) of the beam is accounted for in the formula via the use of Mmax. Mmax is the value you determine the beam to be capable of (100% stress) - which is dependant on Fy. You can find these values directly in the steel manual. 

With the above, you have proven your argument that the weld needs to be larger than the flange - this is all I was intending on helping you with. 

The required thickness of the end plate is a different animal....  There are a number of failure modes, which is more than I could get into here. You may want to look into AISC Design Guides 4 and 13.  Needless to say, these would need to be specifically (re)sized to achieve ductile failure that is weaker than the weld, but stronger than the beam; to achieve your intentions. 

Good luck


-----Original Message-----
From: Mark Johnson [mailto:markajohn(--nospam--at)yahoo.com] 
Sent: Friday, February 26, 2010 12:32 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: CJP Weld in a Moment Frame

Richard,

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.

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.

Thanks,
MJ


--- On Fri, 2/26/10, Richard Calvert <RichardC(--nospam--at)lbbe.com> wrote:

> From: Richard Calvert <RichardC(--nospam--at)lbbe.com>
> Subject: RE: CJP Weld in a Moment Frame
> To: "seaint(--nospam--at)seaint.org" <seaint(--nospam--at)seaint.org>
> Date: Friday, February 26, 2010, 7:22 AM
> Mark,
> 
> The AISC only prescribes the weld of the flanges as moment
> resisting (the web's weld does not count)
> 
> The formula for E70xx, in ASD, would be 0.928*b_f*t_f*16
> > Mmax /(d - 2*t_f) 
> 
> Where Mmax, in your case, would be the maximum allowable
> bending of the member, as apposed to the required
> strength.  
> 
> this wont work - in which case add the additional number of
> 16ths of an inch worth of fillet thickness to the value of
> t_f*16 on the left side of the above equation.  (i.e.
> 1/4" fillet is (4) 16ths, so the left side of the formula
> becomes 0.928*b_f*(t_f*16 + 4)
> 
> but on a side note, unless the beam end was designed to
> realize 95-100% of its bending capacity, then you're worries
> may be a bit overly conservative.  And if it is that
> stressed, you may want to look into RBS joints ilo beefy
> welds
> 
> good luck
> 
> -----Original Message-----
> From: Mark Johnson [mailto:markajohn(--nospam--at)yahoo.com]
> 
> Sent: Thursday, February 25, 2010 6:33 PM
> To: seaint(--nospam--at)seaint.org
> Subject: CJP Weld in a Moment Frame
> 
> List,
> 
> I have an application where I wanted to weld a 50ksi wide
> flange to the face of a 1.25" thick 36 ksi plate and fully
> develop the 50 ksi wide flange.  (it's part of an
> ordinary moment frame)  I think it would be better to
> use fillets, but since it's not my call, I believe it will
> be done with a CJP.  I want to be able to show my
> client that he should add a fillet to the CJP, or else the
> 50 ksi plate won't be fully developed and that the weak link
> will be the interface between the weld and the 36ksi
> plate.  Also, this would produce a sudden brittle
> failure, not a good thing in earthquake country.
> 
> I would like to find an example calculation or an opinion
> on this.
> 
> TIA
> MJ
> 
> 
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