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RARWOOD (Structural) (OP)
5 Jun 07 12:48
I am designing a joint which forms an L shape with a 3/8" vertical Leg and a 3/4" horizontal leg.  On this joint one corner of the vertical plate is touching one coner of the horizontal plate.  I am calling for a 1/4 fillet to fill out the outside area where the two plates touch.  I am using a 1/4" fillet based on the minimum weld size for a 3/4" plate.   I want to add a weld bead on top of the horizontal  plate where it meets the vertical plate.  

For the bead am I required to use a 1/4" weld also?  Or can I go down to an 1/8 bead?
Helpful Member!  Dinosaur (Structural)
5 Jun 07 13:36
I hope you are not arbitrarilly selecting one-quarter inch and that you have checked that you don't need more weld.  Also, if I have the geometric picture correct you will need to use some variety of groove weld if you want to meet any kind of capacity checks.  The weld you describe is a seam weld and I don't know that it has a predictable capacity.  I provide QA in accordance with AWS D1.1 and AWS D1.5 so if you are working to a different code then maybe they deal with this condition.

Good Luck.
RARWOOD (Structural) (OP)
5 Jun 07 17:18
What I am trying to describe is similair to a Double fillet corner weld as shown on page 6.2-9 of "Design of Weldments" by Omar Blodgett.  What I am working on is a U-shaped steel hanger to support a glued laminated wood beam.

I think a simpiler example would illustrate my question better.  If based on the loading I determine a 3/8" bearing seat was required and chose to use all 3/8" plate.  Then the hanger would be made up using two 3/8" vertical plate and a 3/8" horizontal bearing plate spaced 6 7/8" apart for a 6 3/4" wide beam.  

Standard detailing practice where I work, would be to call for a 3/8" outside fillet weld and a 3/16" inside fillet weld.  The 3/8" weld is used because the plate is 3/8" thick and the 3/16" weld is used because that is the minimum size for a 3/8" plate.  

In wood design most conditions are controled by the wood.  In the above example the total shear per side per inch would be 2200 lbs.

What I am trying to do is reduce our welding cost.  Generally I will not use less than a 1/4" weld on the outside because of the quality of welding our vendors produce.  So what I would do for the above example I would use a 1/4" fillet on the outside and a 3/16" weld on the inside.

What I am trying to do is determine if I can reduce the inside weld to 1/8.  As the inside weld gets larger you start to run into clearence problems.  However based on my understanding of the code requirements the minimum fillet weld I can use is 3/16".
Dinosaur (Structural)
8 Jun 07 8:30
Now I understand that the horizontal leg of your "U" will extend past the vertical leg, correct?  This will permit you to use a fillet weld on the outside as you indicate.  I would think that you could consider reducing the size of the outside fillet, possibly to as little as 3/16ths.  I don't think there is any substantial savings in reducing the inside fillet size because a 3/16ths weld is a single pass weld with any equipment I am familiar with.  Reducing it would save almost no labor and a small amount of material unless you are specifying this for 1000s of connections.  Also, using less than a minimum weld size will risk problems with heat effects in the weld as it cools.

If you really want to reduce the welding, you may wish to offer an alternative partial penetration groove weld to your fillet weld approach and let the fabricator choose.  Unfortunately, because of the skill level required, you may not find a shop that prefers to perform the groove weld over a fillet weld.

If it were me, I'd probably go with the smallest double fillet my loads would permit and then move on to something more significant.  Good Luck.
RARWOOD (Structural) (OP)
8 Jun 07 9:50
Thanks Dinosaur for the additional information.

No The horizontal plate does not extend past the vertical leg.  The vertical and horizontal plate only touch at the corners.  The U-shape is produced by having the two outside vertical plates, inside corners touch the top corners of the horizontal plate.  So prior to welding you have a 7 1/2" wide horizontal plane.  3/8" + 6 7/8" + 3/8".

The purpose of reducing the inside weld is not to save steel fabrication costs, but to increase clearance between the weld and the wood beam.  The design intent is to have the wood beam bearing only on the horizontal plate and not on the weld.  When a large weld is used, it requires the beam to be camfered for weld clearance.  There are times this is done but there are other times when providing a camfer is undesirable.  For exampl I have a current job where a 70' long beam requires a 3/4" camfer full length on each bottom corner to clear welds at multiple connection plates.

I think you answered my question however.  I know the use of a minimum size  fillet weld assures that a thick plate does not draw heat away from the weld resulting in a improper weld.  I thought maybe my case was a little different because it seems when you place the inside weld you are mainly adding weld to existing weld.  However you indicated that using less then the minimum weld can cause problems as the weld cools.  

I would like to use more groove welds but don't feel that the typical small steel shops I work with have welders that understand how to do a proper groove weld. For a similair reason I almost always don't use less than a 1/4" fillet weld on the outside.

With some of the vendors I have worked with welding seems to be a real challenge.  I have seen welds left off.  On one job where the shop made up u-straps, they welded both vertical plates to the back plate but only welded one vertical plate to the horizontal plate.

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