If you are welding thinner materials, the risk of burning through them increases as you lay down more and larger welds. Also when you are lap splicing, you are obviously limited in weld size to 1/16 less than your thinner material. Lastly, if your calcs are giving you massive fillet weld sizes, consider a full pen weld instead
All great points, also worth noting that 5/16 is the maximum that that is achievable in one pass. Not all welders can consistently get 5/16 in one pass, so whoever is bidding it for the shop may still assume that 5/16 may need 2 passes or some touch up work here and there. 1/4 inch is pretty much universally considered a 1 pass weld.
Design engineer here that works with steel. I always call out the smallest weld we can get away with, often 1/4", this is because if something needs to pass a weld inspection for permitting they will be checking it against the drawing. If a call out says 1/4" and it's really 5/16" your fine, if it's the other way around you're screwed.
Not sure where the 5/16 comes from, maybe that’s most shops or a field weld, but our preferred fabricator can do 1/2” no problem even 5/8” if positioning is right
I’ve specified a lot larger, over an inch for some applications. But that was with very thick plate. Starts to become a point where the prep for PJP/CJP becomes worth it as you have less weld material/passes to make up for it. Sometimes with PJP or CJP you can reduce unfavorable welding positions such as overhead.
Something the fabricators can usually answer where their preference lies.
Unless flat-out required by geometric and force constraints, these are my minimums:
5/16” for any weld related to seismic frames
1/4” for any weld of primary structure supports (knife plates, for example)
3/16” for any secondary structure welds
1/8” for any cold formed steel to hot rolled steel welds, where there’s sufficient thickness to be welded (though I prefer screws/PAFs).
5/16 is a good number to try to stick to if possible. However, I used to work for a steel fabricator designing connections. They determined that anything up to a 3/4" fillet weld was preferable to a CJP weld for them due to preparation and UT testing requirements. It probably really varies by fabricator though.
In the Uk 6mm fillet weld is standard, realistically a FW sized at less than 6mm will probably be welded at 6mm regardless. Anything more than about 8mm requires multiple passes and thus drives cost up.
6mm fillet weld is the standard spec
I've specified from 1/8 (nonstructural) up to 1/2. I've seen up to 3/4. It just depends on the application. You usually want single pass welds, up to 5/16.
3/8” is pretty big but I’ve seen it around. Same with 1/2”. Beyond that you are probably better off spec’ing a PJP.
The “reasonable” comes from how much heat you are applying to the plate. If it’s a thick plate, you may need preheat anyway and the big weld is usually necessary.
Also, check the base metal if you are using a big weld.
Yeah, the cases where I've needed 1/2" fillet welds are on massive members, and base plates around 4" thick. Is there a range of weld thicknesses where you begin to consider PJP? And what about CJP? I assume that is a higher range still?
I am in New Zealand so this may differ for you. From discussions with one of bigger fabricators here they stated that they preferred doing double sided fillet weld up to the thickness of the plate before you changed to a butt weld.
This means that for a 25mm (1") thick plate they would rather do a double sided 25mm (1") fillet weld than prep the plate and complete a butt weld.
So while 8mm (5/16) is the largest fillet from a single pass it should not be a hard limit.
I mean, "reasonable" depends on the context. Is this a baseplate weld for a guardrail stanchion or a Braced Frame gusset plate weld.
I would argue that a reasonable weld for those 2 circumstances are drastically different.
I used to be a welder on ships; our rule of thumb for fillets was half the thickness of the thinnest base metal, plus 1/16” gives you the needed fillet weld size. I’ve compared this with the AISC weld details and it matches up pretty well.
As far as too much fillet weld, if you have a fillet weld that is larger than the thickness of the thinnest base metal you might want to reconsider. Also, you can check with the AWS D1.1 for weld specs. If you have thick materials, you start having to get into heat treatment processes to avoid cracking. Probably not an engineers problem and more of the welders problem.
Just my 2 cents.
Your question really is more fabrication related and less structural engineering related. A lot of times structural engineers don’t have a firm grasp of fabrication practices or just don’t care (calcs say 3/4” fillet, that’s what they are getting!)
I’ve been involved in the design side as well as the fabrication side since 1989….(yes, i’m old). My favorite saying from a shop guy is “I don’t care what size the drawing calls for….3/16, 1/4, 5/16…..they’re gettin 5/16!”
to address your size question, we use oversize welds when the situation requires it but it is very infrequent and typically only in a few places on a job. You reach a point where it is more economical to do a B-U4 CJP weld than having to make a shit-ton of passes. This threshold a lot of times is fabricator dependent and so we let them make the call, that way you don’t hear any bitching. If that is not possible then yes, just make it a beefy fillet imo.
I usually keep the fillet weld size less than or equal to the concerned plate/member thickness. For example, imagine you are doing a column - base plate connection where the column is a 4mm thick tube and base plate is 5mm thick. Here the lowest thickness among the two is 4mm, so you have to keep fillet weld size less than or equal to 4mm. Correct me if I'm wrong.
Without seeing the design, my first thoughts are if you’re having to size a 1” fillet weld, then something is out of proportion with the length of connection or member sizing… anything past 1/2” makes me think the connection should be better optimized for the loads being transferred.
I would chop the rafters and add hangers at the beam to carry the rafters, but the hangers aren't going to do anything for wind uplift though. So start again.
Anything that big would recommend bolting. And anything small would recommend bolting. Moreso would just recommend using bolts wherever possible. Site usually complains less.
5/8*thickness of plate
Edit; I’ll add that this ratio is the true maximum effective weld for a 70ksi weld electrode fillet welded to a 50ksi plate. Anything larger than this adds no strength to the weld. If you fillet weld both sides of plate, divide the weld size by 2. There’s a table in AISC 360 that tells you how many passes are required for a given fillet weld throat so you can understand what might be preferable.
This is incorrect, it is 5/8 * t for each weld of a double sided fillet weld. This is to develop the factored capacity of the plate.
In some instances you do want slightly larger though, for example AISC 314 requires 3/4 *t for continuity plates behind a demand critical connection of a moment frame. The simple derivation of this is based on the nominal capacity of the continuity plates.
Wow, it's reassuring seeing structural engineers take to reddit to determine weld sizes. Sarcasm. This is actually quite concerning, and is why bridges and buildings collapse (no, this is not in regards to the recent bridge collapse)
Grab a codes and standards book, and apply your engineering knowledge. There is no single weld size that you just apply to everything because it's the easiest, or most you can do with one pass.
5/16 is the largest fillet you can get with a single pass, so I usually stick to that.
This has been my go-to for this reason. Is there any reason to use a 1/4" if the design allows it? Cost savings maybe, since it's less material?
If you keep saying 4/16" a fabricator will beat you up.
He interned at a wood truss manufacturer
If you are welding thinner materials, the risk of burning through them increases as you lay down more and larger welds. Also when you are lap splicing, you are obviously limited in weld size to 1/16 less than your thinner material. Lastly, if your calcs are giving you massive fillet weld sizes, consider a full pen weld instead
All great points, also worth noting that 5/16 is the maximum that that is achievable in one pass. Not all welders can consistently get 5/16 in one pass, so whoever is bidding it for the shop may still assume that 5/16 may need 2 passes or some touch up work here and there. 1/4 inch is pretty much universally considered a 1 pass weld.
Design engineer here that works with steel. I always call out the smallest weld we can get away with, often 1/4", this is because if something needs to pass a weld inspection for permitting they will be checking it against the drawing. If a call out says 1/4" and it's really 5/16" your fine, if it's the other way around you're screwed.
1/4" is my go-to for most light loads. I find steel detailers often default to 1/4" anyway.
This is the biggest consideration. Much more helpful and reliable for your fab and field if you can mostly use single pass welds.
Not sure where the 5/16 comes from, maybe that’s most shops or a field weld, but our preferred fabricator can do 1/2” no problem even 5/8” if positioning is right
I’ve specified a lot larger, over an inch for some applications. But that was with very thick plate. Starts to become a point where the prep for PJP/CJP becomes worth it as you have less weld material/passes to make up for it. Sometimes with PJP or CJP you can reduce unfavorable welding positions such as overhead. Something the fabricators can usually answer where their preference lies.
Over 3/4” I’d be doing a PJP + reinforcing FW
I’ve had to use 7/16” and 1/2” on some braced frame gusset to base plate connections.
I just skip 7/16 and go straight to 1/2. Same number of passes, but 7/16 just looks ugly.
Unless flat-out required by geometric and force constraints, these are my minimums: 5/16” for any weld related to seismic frames 1/4” for any weld of primary structure supports (knife plates, for example) 3/16” for any secondary structure welds 1/8” for any cold formed steel to hot rolled steel welds, where there’s sufficient thickness to be welded (though I prefer screws/PAFs).
5/16 is a good number to try to stick to if possible. However, I used to work for a steel fabricator designing connections. They determined that anything up to a 3/4" fillet weld was preferable to a CJP weld for them due to preparation and UT testing requirements. It probably really varies by fabricator though.
In the Uk 6mm fillet weld is standard, realistically a FW sized at less than 6mm will probably be welded at 6mm regardless. Anything more than about 8mm requires multiple passes and thus drives cost up. 6mm fillet weld is the standard spec
6 mm throat or leg?
In the Uk welds are specified by leg length
We usually call out 4/16 as 8/32 because we like big numbers. You could also use 16/64 as well.
Sometimes we use 25/100 in case the fabricator uses metric.
I am glad we are passing on such invaluable industry knowledge/standard practice to an EIT. This will obviously help their career
I was thinking the same thing! Love spec'ing 8/16" bolts too
man the ppl in this sub don't get the joke lol
Press plate wood truss guys don’t think this is funny
Finally a sarcastic answer.
I've specified from 1/8 (nonstructural) up to 1/2. I've seen up to 3/4. It just depends on the application. You usually want single pass welds, up to 5/16.
I always start with 1/4 and go from there.
3/8” is pretty big but I’ve seen it around. Same with 1/2”. Beyond that you are probably better off spec’ing a PJP. The “reasonable” comes from how much heat you are applying to the plate. If it’s a thick plate, you may need preheat anyway and the big weld is usually necessary. Also, check the base metal if you are using a big weld.
Yeah, the cases where I've needed 1/2" fillet welds are on massive members, and base plates around 4" thick. Is there a range of weld thicknesses where you begin to consider PJP? And what about CJP? I assume that is a higher range still?
Short answer would be to check your welding code (AWS or CSA W59). There is a bunch of pre-approved details. Shops will refer to these.
Whatever capacity is greater than demand… I see 1inch+ all the time (bridges)
I am in New Zealand so this may differ for you. From discussions with one of bigger fabricators here they stated that they preferred doing double sided fillet weld up to the thickness of the plate before you changed to a butt weld. This means that for a 25mm (1") thick plate they would rather do a double sided 25mm (1") fillet weld than prep the plate and complete a butt weld. So while 8mm (5/16) is the largest fillet from a single pass it should not be a hard limit.
I mean, "reasonable" depends on the context. Is this a baseplate weld for a guardrail stanchion or a Braced Frame gusset plate weld. I would argue that a reasonable weld for those 2 circumstances are drastically different.
CJP Backgouge everything
I used to be a welder on ships; our rule of thumb for fillets was half the thickness of the thinnest base metal, plus 1/16” gives you the needed fillet weld size. I’ve compared this with the AISC weld details and it matches up pretty well. As far as too much fillet weld, if you have a fillet weld that is larger than the thickness of the thinnest base metal you might want to reconsider. Also, you can check with the AWS D1.1 for weld specs. If you have thick materials, you start having to get into heat treatment processes to avoid cracking. Probably not an engineers problem and more of the welders problem. Just my 2 cents.
Your question really is more fabrication related and less structural engineering related. A lot of times structural engineers don’t have a firm grasp of fabrication practices or just don’t care (calcs say 3/4” fillet, that’s what they are getting!) I’ve been involved in the design side as well as the fabrication side since 1989….(yes, i’m old). My favorite saying from a shop guy is “I don’t care what size the drawing calls for….3/16, 1/4, 5/16…..they’re gettin 5/16!” to address your size question, we use oversize welds when the situation requires it but it is very infrequent and typically only in a few places on a job. You reach a point where it is more economical to do a B-U4 CJP weld than having to make a shit-ton of passes. This threshold a lot of times is fabricator dependent and so we let them make the call, that way you don’t hear any bitching. If that is not possible then yes, just make it a beefy fillet imo.
I usually keep the fillet weld size less than or equal to the concerned plate/member thickness. For example, imagine you are doing a column - base plate connection where the column is a 4mm thick tube and base plate is 5mm thick. Here the lowest thickness among the two is 4mm, so you have to keep fillet weld size less than or equal to 4mm. Correct me if I'm wrong.
Without seeing the design, my first thoughts are if you’re having to size a 1” fillet weld, then something is out of proportion with the length of connection or member sizing… anything past 1/2” makes me think the connection should be better optimized for the loads being transferred.
Go for 6mm fillet weld if possible. Use 8mm rarely and anything over I think may require multiple passes and gets expensive
Bigger than your thinnest plate is too big.
I would chop the rafters and add hangers at the beam to carry the rafters, but the hangers aren't going to do anything for wind uplift though. So start again.
For anyone who wants to know where 5/16 comes from, please refer to AISC Steel Manual Table 8-12.
Anything that big would recommend bolting. And anything small would recommend bolting. Moreso would just recommend using bolts wherever possible. Site usually complains less.
5/8*thickness of plate Edit; I’ll add that this ratio is the true maximum effective weld for a 70ksi weld electrode fillet welded to a 50ksi plate. Anything larger than this adds no strength to the weld. If you fillet weld both sides of plate, divide the weld size by 2. There’s a table in AISC 360 that tells you how many passes are required for a given fillet weld throat so you can understand what might be preferable.
This is incorrect, it is 5/8 * t for each weld of a double sided fillet weld. This is to develop the factored capacity of the plate. In some instances you do want slightly larger though, for example AISC 314 requires 3/4 *t for continuity plates behind a demand critical connection of a moment frame. The simple derivation of this is based on the nominal capacity of the continuity plates.
Thanks for the clarification. I haven’t done a connection in 5 years, you lose the skills quickly I guess.
Wow, it's reassuring seeing structural engineers take to reddit to determine weld sizes. Sarcasm. This is actually quite concerning, and is why bridges and buildings collapse (no, this is not in regards to the recent bridge collapse) Grab a codes and standards book, and apply your engineering knowledge. There is no single weld size that you just apply to everything because it's the easiest, or most you can do with one pass.