max weld size question

huangyhg

max weld size question
i'm connecting a 1/8" thick tube to the bottom flange of i-beams varying in thickness from 1/4" to 7/16".  sec j2.2b of asd states that the min weld thickness depends on the thicker of the 2 parts joined and is per table j2.4.  
for the max size fillet weld it states that for material less than 1/4", the weld is not greater than the thickness of the material.  does this mean the thicker part also? or the thinner part?  if it goes by the thinner part than my max weld would be 1/8", but for i-beams flanges above 1/4" thick, my min would be 3/16" (greater than the max).

what you wrote is correct. for 7/16 thick flanges minimum weld is 3/16". however for 1/8" thick material, maximum weld size is 1/8". but it doesn’t mean that code is wrong. i have a feeling that you cannot furnish this connection as per code without reinforcing hss web by adding plate. check with aisc design guide for hollow sections (d/t limitations etc).you will see that all will add up. also look into the capacity of welds little bit. like a fillet weld with one leg 1/4 and other 1/8 will have capacity of 1/8.if you can provide me connection lay out, i can be more specific. excellent source is descon software, it will take you step by step to options you can have.
i am assuming in the connection you describe that the tube walls are perpendicular to the beam flange, so that you have a tee joint.  the max. size of fillet welds in j2.2b is intended for lap joints, not for plates that are lapped.  the reason for the max limitation is that the exposed upper corner of the plate edge tends to melt into the weld, and this can reduce the effective throat of the weld.  volume ii connections explains this on page 2-44.
if you are lapping thin plate to a relatively thicker beam flange, the weld size doesnt exceed the thickness of the thinner part, but there has to be adequate preheat to avoid cracking.  hope this helps.
someone more qualified than i am should write a max weld size faq.
hg
i just reread my post and noticed a huge typo.  
in the first paragraph, the second sentence should read "the max size of fillet welds in j2.2b is intended for lap joints, not for a tee connection where the plates are perpendicular to eachother".  
with tee joints, you don't have melting of the corner as when the plates are lapped.
sorry for the confusion.
thanks bjb.  the joint is a "t" joint.
this clarifies the "that is permitted along edges of connected part" in j2.2b for the maximum size of fillet welds permitted.
just a few points to add:
1. in the 9th edition of the aisc-asd spec, min size(leg) of fillet weld per table j2.4 is based on material thickness of thicker part joined.
2. the aws reference the 9th edition of the aisc-asd spec for bldgs was based on is one from the 80s.
3. in the latest aisc spec for structural steel bldgs (2005), the min size of fillet weld in table j2.4 is based on material thickness of thinner part joined
4. the corresponding table for min fillet weld size in aws d1.1 (96 edition onwards) is table 5.8..variables like low hyrdogen/non-low hydrogen, preheat etc can determine whether the thicker or thinner member joined govern the min size of weld. aisc modifies this table.
question: even though aws d1.1 does not stipulate a maximum requirement for fillet welds used to attach tubular   
bagman- yours truly recently specified an 1/8" plate to be welded horizontally to the bottom flange of a w16x26 (for supporting some light gauge), with a one inch long 1/8" fillet weld spaced six inches apart.  the welds ended up looking pretty ratty (i think because the 1/8" pl thickness was a challenge for this particualr welder), and the 1/8" plate ended up badly wrinkled and distorted by heat (to the point it had to be cut off and redone) after welding.  if the fabricator is on board suggest discussing that with him.  consider using a thicker plate just to minimize these issues, even if it isn't the most efficient use of material.  regards
in my impression, the maximum all-around fillet weld size of hss connections is not limited the the thickness of the thinner part. the weld size can be larger than the hss wall thickness. i saw some tables like that. correst me if it not right.
figure 6 on pg 7.4-3 of blodgett's design of welded structures seems to confirm what bjb is saying about the max weld size being for lap joints.
j1d, the maximum fillet weld size is controlled by the thinner part.
for thicknesses up to and including 3/16" the maximum weld size is the thickness of the material.
for thicknesses greater than and including 1/4" the maximum weld size is the thickness of the material - 1/16".
so the maximum thickness of fillet weld for a 5/16" angle welded to a 3/16" tube is 3/16".  and the maximum weld for a 3/8" tube fillet welded to a 5/16" tube is 1/4".