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Re: Tack Welds

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Stan,

AWS D1.1-2002 actually has requirements for Tack Welder qualifications in Chapter 4 and Fabrication requirements in Chapter 5; specifically section 5.18 "Temporary and Tack Welds".  However you will not find anything on strength provided and the reason has to due with what Rick Drake mentioned earlier.  That is, welds have a minimum length required in order to build up the necessary heat input (i.e. overcome the parent metal heat sink)  to create proper metal to metal fusion.  A tack weld is not large enough nor is it long enough to develop this and therefore any strength created is questionable.

As mentioned before, the best you can do is actual testing of the complete structure or system.  If this can not be done in place then you could try and recreate the same truss and welding and independently load test it.  Or as you mention below recreate the actual connection (same angles and weld) and test several of these to see 1.) what the potential strength is and 2.) what is the standard deviation (i.e. how variable the results are).

Obviously a tack weld has some strength but as you said do they have "reliable" (and consistent) strength.

Thomas Hunt, S.E.
ABS Consulting




"Caldwell, Stan" <scaldwell(--nospam--at)halff.com>

06/20/2003 09:18 AM
Please respond to seaint

       
        To:        'SEAINT Listserv' <seaint(--nospam--at)seaint.org>
        cc:        
        Subject:        Tack Welds



It has always been my understanding that tack welds are temporary welds that should not be relied upon for the permanent connection of structural members.  In addition, since tack welds are not prequalified, their strength cannot be calculated, and must be determined through an approved (by the EOR) program of load tests on actual welds made at the jobsite at the start of construction.
 
Nevertheless, I have recently been asked to calculate the reliable shear strength (allowable or ultimate) of 1/8 in. diameter tack welds connecting two small angles (open-web steel joist chords and bridging).  As far as I can tell, there are no provisions for this in either AWS or AISC.  I am about to conclude that these welds have no reliable strength.  Am I missing something?
 
This is not an academic question, as it is about to become the central issue in a $4.3 million lawsuit (I am neither plaintiff nor defendant).
 
Thanks in advance for your brilliant responses!
 
Stan R. Caldwell, P.E.
Dallas, Texas
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