Rule Of Thumb For Fillet Weld Size

[Veer007]

Hey guys
This may sound silly,
If forces are unknown, is this a good practice to determine fillet weld size by the below table? Also, fillet leg and fillet size are the same?

Thanks in advance!!

 

[r13]

I think the rule of thumb can be used for a large project, with many secondary/miscellaneous connections that do not have/carry structural significance, to facilitate the project manpower utilization, and construction flow. Similar to the note "all bolts shall be A325 5/8" diameter....u.n.o."

 

[phamENG]

retired - I think I see what you're getting at, and I agree with the concept. But I would say that's not a rule of thumb. By all means, take all (or some reasonable grouping) of similar connections and provide one design based on the worst case loads. But design it for the load and not based on a rule of thumb.

 

[r13]

I think you are too focus on the name "rule of thumb" of the table. Rather it is a guide to minimize the unnecessary guessing when detail are not present, but the word in spec for such situation - "see table". The table does not rule out the engineer's duty to provide detailed design, and at least to filter out the suitability to refer to such table. I think that's the intent of the author who made the table - a design aid.

 

[mfrad]

Veer007,
Your table came from Omer Blodgett's, "Design of Weldments" which is a good start.
Everyone's comments are solid information. I added two tables from AISC as my starting point and I hope it will help you zeroing in on the weld strength or plate size. I would memorized Table 3.2 to know the minimum weld size that I need for the steel plate being used. This is a mimimum bound on the size. The upper table gives you the minimum plate thickness for Grade 36 and 50, so that the weld size D strength for double sided welds can be developed. For a single weld line use 3.09 vs 6.18 so the plate thickness required for that weld will be half. (I added the formula for plate thickness to calculate for other grades of steel, this table is based upon E70 electrodes.)

Must check shear and tension strength of the plate too, then you will have a range of the connection capacity for design or analysis.

 

[IFRs]

This might be considered a double post, see thread 507-471129

https://www.eng-tips.com/viewthread.cfm?qid=471129

 

[phamENG]

IFRs - I disagree. There's a good month between the posts, and in the one you referenced he's asking if there is a calculation to better determine MINIMUM weld size. Here, he's looking for a rule of thumb to use when designing - not what the minimum size is (though some of the discussion has gone back to that).

 

[Veer007]

Guys if this is T-joint, if 3/16" weld is enough for given force when I have 3/4" thick plate as thinner part, I should not use, right? So I have to go with 5/16" min weld as per J2.4,

Where would you recommend this rule of thumb table ? can you advise me on the conditions?

Also, is there no conditions that weld size rely on plate thick? nowhere?

Thanks in advance!!

 

[desertfox]

Hi veer007

Can you give details of the joint you are trying to weld, if this is a tee joint can it be welded on both sides? Also if the thinner part is 3/4” thickness then the table you posted suggests a 9/16” weld to develop full strength.
To get the best answer we need to know what exactly you are welding and it’s function otherwise we are making assumptions and second guessing and you won’t get a correct answer.


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Veer007]

I can't have UDL for tube sections from CISC.

below is the connection that will show you details, connection plates are 3/4" thick mentioned by EOR.

Thanks in advance!!

 

[desertfox]

Hi veer007

Have you another view of the section? Is it a “c” section you are welding, I can’t tell from one view what exactly you are trying to do. Are you welding the blue section onto the yellow bracket?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Veer007]

Both yellow are connection plates, the blue one is Girt HSS254x254x12.7 and Pink is w-column

Thanks in advance!!

 

[mfrad]

Veer007
Blodget's table is not based on weld strength, nor plate strength. Fillet sizes are proportional to either E60, E70 or E80 welding rods. His book covers both building and machine design. In buildings the bottom half of the table fillet welds are not economical, suggest dropping fillet weld greater than 3/8 for buildings. The right column (33%) with asterisks is AISC the thinner plate weld size. PhamEng has clearly stated in his earlier response thread that thickness also relates to preheat requirements.

Your last sentence indicates 5/16ths weld. You can use intermittent spacing as one alternate. Therefore Blogetts table is not that useful in itself.

 

[desertfox]

Veer007

So the yellow plates sit on either side of the HSS section?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Veer007]

No, one is a gusset plate and another one is the connection plate which slots the HSS tube.

Thanks in advance!!

 

[desertfox]

Hi veer007

So the a plate is welded central in the HSS tube And then using bolts that plate is fastened to the gusset plate is that right ? Also how is the HSS section loaded when in position?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[phamENG]

Veer - let's back up for a second. You say the following:

I can't have UDL for tube sections from CISC.

Do you mean that the EOR put said to design all connections for 1/2 UDL values but the code you're using doesn't have UDL values for HSS? If that's the case, stop guessing. Stop trying to use rules of thumb. Stop doing anything but sending an RFI to the EOR and requesting a reaction because they failed to give you one. You're designing connections on behalf of the fabricator - the EOR is responsible for analysis of the structure. Get the data he/she is required to give you and don't roll the dice. It's not worth it for you, your employer, or the people who may one day walk into that building.

 

[Veer007]

I greatly appreciate all your point. You are my one of inspiration.

I never going to do anything without confirmation or getting approval from EOR.

What was my concern is, Is this a good practice to follow thumb rule when there is a case, That we are not sure about load but we know the thickness of either bare/connected plate thickness.

I know a real engineer never going to use this thumb rule/J2.4 at anywhere without knowing force, but I want to say one thing, in detailing industry EOR never going to address each and every location, we also have to take some decision without EOR interference. In deep, EOR never gave us proper forces at all locations instead of saying connect for 50% UDL or full capacity of a member.

If we have to connect steel for its full capacity we end with larger weld, Meantime contractor pushes the fabricator for expediting deliver the steel to site.

We generally ask torsional force, axial force, moment forces, and lateral force... But if come to the point, we have to connect column with Beam/HSS for shear force using handbooks.

Also if connections seem too scary, we have to raise RFI states is this fine or not? Then they are changing original contract dwg.

So we often look for thumb rule that ends with better performance as well as safety too, we connection designer never going to do if something is not proper connection even if fabricator prefers, we will inform him/her that we should use this for better performance.

All these processes leads to more time than expected.

Thanks in advance!!

 

[dauwerda]

This is a bit off topic, but I would prefer to see that connection made with a WT or an end plate welded to the HSS so that the shear is directly transferred to the web of the HSS rather than through bending of the flanges.

 

[phamENG]

Veer - I would say the only time to use a rule of thumb would be to put a cost estimate together. Preliminary design phase, rules of thumb are a good tool to get in the right ballpark and set everyone's expectations. Once you get past that, stop using them. If you find yourself in a situation where the EOR is failing to do his/her job, and you have no choice but to design for the "full strength of the member" (which is a pretty loaded requirement and can have some seriously complicating repercussions if you take it far enough), then don't use a rule of thumb for it. Figure out the capacity of the member and use that number to do actual calculations.

 

[Veer007]

Apologies, if this is irrelevant I just want to say the fact.

Thanks in advance!!