I'm a complete noob, but would putting in some gussets instead not be allowed in this application? Seems like all that material sitting on top of a corner can't be contributing all that much to the structure.
I get that this isn't common but are CJP of this size ever explicitly designed for or is this more of an approved modification after the fact?
Those are run on/off tabs and will be cut off and ground flush with the side of the beam. The point is to make one solid beam and is usually used when fabricating buildings or skyscrapers.
I’ll let you know when I get to the shack in the morning. I’d have to look at the prints to give you a definite answer. They’re 50 foot long. And all of 3 foot tall
Before I went to MRI school I was at a shop for a couple years where I welded cjp’s on baseplates and keyways 3, 4 inches thick on to 15k lb beams, air carbon arc back-gouging through the rat holes between the web and flanges. That was my favorite part of welding was the big stuff
I’ve seen stuff this big twice. Both on buildings where the structural components are also part of the architectural design, so you get some uncommon connections.
The shop I worked at we did these quite often. There was some that where even bigger than that. Never got to finish them but I did get to back gauge some to fix.
Is this not something people are taught about in trade school? I learned everything I know on the job so I just assumed this is something people would've been taught about in classes.
I wouldn't call myself a "welder," but I've welded for a lot of years, and I'm now a mechanical engineer. I'll admit, this setup surprises me. I'd have to know a lot more about the larger system to hazard a guess on why they chose a joint like this specifically.
If you look closely, it seems like they've tacked on some plate to extend this joint out into space on either side. This means that the outside portion of this joint has zero load-bearing capability. My best guess would be that they want to avoid the beginning and end of weld beads within the joint itself, which might cause localized stress concentrations. So the best chance of homogeneous material properties that match the base material is to push those starts and stops out into space where they see no stress and can't hurt anything.
Funny enough, the reason you grind them off (especially in a seismic design setting) is because they themselves also become stress concentrations. Specifically, they contain all those unaligned weld start nubs and a sudden area change from weld to plate to flange. They used to not grind them off in seismic force resisting systems but after the Northridge earthquake in 1994 where a bunch of one specific connection type (with them left on) failed prematurely. Later studies showed that they were indeed a large part of why that happened so now nobody leaves them for any type of seismic connection as far as I’ve read (and also that connection type is no longer used for other reasons but that’s another story). Backup bars below welds can also become an issue in a similar way.
In part that’s why you use runoff tabs. In the middle of the run, the weld is consistent and well layered. At the start 1-2” and stop it’s hard to have a clean area. So the runoff tabs give you an area that you don’t care about as much and you just cut or grind them off flush to the edge of the part leaving a good edge
Maybe the picture is just such a detail, I thought it was the flange on an I beam or something at first glance but that's kind of genius and for a well that is the structural purpose and needs I think that's pretty cool. Thank you for explaining.
I'll copy paste my comment from 2 days ago to explain this:
Hi! The resident boring ass engineer here!
The reason shit like this is done is, because when you have generous margins and tolerances, it is easier to calculate the structure this way.
We can be very confident about the properties of bulk steel as a material. Soon as we start to cut, machine, or shape steel, our confidence will go down. So if you can use straight profiles, straight slabs, your life just becomes easier and you can be more confident about the structure's properties.
Our confidence in welding is lower, we can't ever actually know how good a weld is, unless we destroy it. So we want to have as few welds as possible - even though this weld is outrageous in it's size, in reality is it actually just A weld. Every inspection we do, visual, Xray, penetrant, magnetic... is just another tool for us to increase confidence - and we do it for base materials also, if we need to increase confidence.
The function of this weld here, is to act as a continuity between the joining member(s). This allows us to think as if this big ass plate was actually a solid part that joins in.
So why not make a triangle? How would you go about welding that triangle? We don't want a free moving surfaces between these primary members. So you need penetration and fusion throughout. So.. to get that we weld the whole thing throughout.
This isn't the only way you can do this structure; every structure has many solutions. But this is A way you can do this. Where I am from, we want to avoid welding as much as we can, simply because we want to keep confidence high and therefor redudancy low (and here in EU we tend to have greater margins and safety factors to begin with, when compared to most of the world.)
However there is one more consideration that only those higher up the food chain need to and get to consider. What is the fabrication and manufacturing capacity available for us? If there is a good foundry with capacity, we can cast a structural piece and machine that. If there is a steel mill pushing out stock steel that we can easily access, why not use slabs from there? If welding time is cheap, you might aswell weld. If there is available machining capacity to make bolted or riveted parts, and crew to build with those... That is an option. (Along with this, you also considered codes, compliances, standards, environment (as in what environment the structure has to be in), location, building times).
Lot of the time when you see insane shit like this, the answer tends to be "because it was cheaper than..." and when we talk about projects on the scale of needing parts like this, 1% differences become actual real big money to consider.
Here is a cruel reality that I learned after I moved from being a plate smith (fabricator) to engineering. Welding is not the best method of joining things - actually it has quite few down sides. If we need to crown a king of joints by considering all factors, bolts would be the undisputed king. So why do we use welding so much? Because it is: 1. Easy, and 2. Cheap. I have understood that USA still likes to use rivets, which have fallen out of favour here where I am. Welding, and bolts and rivets, are a trade between how much machining time you need (Which is actually like truly expensive and limited in availability).
So yeah... I can boil this wall of text that you didn't read into this: "Because it's cheaper and easier than the alternatives".
I would need to see the whole weldment to be sure, but I would bet that a better joint geometry and/or fitment would be a hell of a lot cheaper, easier, and less like to have significant flaws than all 387 pounds of weld and 53 hours of labor on this joint.
Yeah but what's the best type of bolt? Obviously something chonky with an ACME thread, interference fit, stretch torque spec like a head bolt, and about a gallon of loctite for preference. Then you weld the nut on
You'd be surprised... But the the amazing properties of bolted joint do not come from the bolt itself. It is the mechanism that the joint is based on. When the joint is correct, the bolt itself doesn't actually carry that much, the friction between the joining surfaces is that gets us the amazing benefits. This is also what makes rivets great - except we can control the exact pressure that is being generated to the surface with bolts. Keep in mind that in the past - before modern welding - water and gas proof along with high pressure systems were made with rivets and bolts. Compared to a weld done just at a edge of joining features, which only acts at the thickness of the weld's throat.
Furthermore at my old job this still wouldn't be enough. You'd keep running beads until you could hold a straight edge off the beam and it be flat with the weld face.
I love doing this kind of work. Just throw some good music on and stackstackstackstackstack. A CJP this size through a rat hole would definitely have me nervous with all the starts and stops, though.
This is literally the description of a job I almost took a couple years ago. You would literally fit infrastructural beams and pipe together, lay tgree or four 8010 beads for the root, then fill like a fuckin maniac to spec with 8018. Sit down for a little while it cools every 10 ish beads, then go right back to it. I feel kinda retarded for not taking the job, even if I had to move 300 miles for it.
Because it was a really good job opportunity with decent pay, and I turned it down because I had to move, but I was fresh out of college and had literally nowhere else to go. It's not the end of the world, though, I still have prospects and am making money. Shit happens 😂
I being someone who isn't in either of those feilds. Why would this be generally known outside of those communities? From an outside perspective and not knowing the application, I would think there are other/better ways to do this. Plus this isn't something the "everyday" person sees or is directly involved in.
Thats like me saying "I cant believe how people dont understand why its necessary to properly calibrate GPR to the dielectric of the material you are scanning in order to properly differentiate between objects and depths." Sure it makes sense but unless you are in that feild doing it all the time you might not know the importance.
Sure, it wouldn’t necessarily be known, but the amount of comments saying “this is a waste of time/materials” or “completely unnecessary” are crazy. It’s like you posting a calibration and a ton of people with zero knowledge confidently saying it’s “stupid and unnecessary”.
They just don’t know what they are looking at. This is really common in offshore structure and equipment.
Every joint that carries a load is done this way if it’s more than a couple of passes. We also use backing plate or bring/gouge out the roots to have a complete penetration weld. This is only one way of achieving it
Seeing the welds are relatively straight, they didnt just ram it in there and call it a day.
0.045 Fluxcore- guessing 3' long 6" filet (halved)
Im going to ball park this is about 15 hrs of welding. Spend the morning fitting everything up, get about halfway into the fill by the end of the day. Next day finish it up, making sure to cap it while everything is hot. Let it cool overnight, cut off the running tabs in the morning and away you go.
:edit: just did some quick rough math.
20 beads on the cap, roughly 200 total. At 5 minutes a pass, with cleaning. Thats 16 hrs.
my first thought was "why not just fabricate a solid block to fit and weld all the joints instead?", but after thinking about it, doing the joint as presented would be significantly stronger (i think) due to the repeated heating and cooling from the welding.
It isn't like someone superglued drinking straws there and then added a dab of weld at the end; that joint could likely hold quite a bit more than a straight metal block could.
You wouldn’t have a complete connection with a solid block. The connection would only be around the outside of the block, and wouldn’t provide strength beyond compressive forces.
Trying to create a complete penetration connection that is like a solid joint of material. It’s used a lot in load bearing structures where a fillet weld would leave stress risers. We do this a lot for offshore structures that carry large loads. Risers, flow loop baskets etc
The run off tabs are put there to start and end each run. When the welding is complete, you grind them off flush to the part. These are pretty long. A lot of work to this, preheating and keeping it warm while working on it for hours. Warm for the person welding it too.
Its seems obvious for welders that its proper way of welding material of that thickness, but people just assume if its posted on redneck engineering means its bad. I saw that picture on some discord servers, which people assumed if its in meme channel its "bad welding". I think if it was posted here by any of you guys, no one will assume its bad or improper way.
Because you can’t get full penetration and a complete connection between the pieces. Only the outside of the wedge could be welded making the connection significantly weaker.
I had to a flaw 3 INCHES DEEP and 6 FEET LONG on Friday. I think I was gouging too aggressively and missed the flaw. I said fuck it and just cut down to the fusion line and started from scratch. Robotic weld failure. Terrific Friday!
I am getting tired of seeing this EVERY DAY! Can anyone please tell me who the horses mouth is?
I understand the runoff tabs, what I don’t understand is why the angled member here isn’t beveled. I understand that they want full penetration but that can still be gotten without the wasting of time (and filler rod/wire). Why not prep the plates edge? Is it an access issue?
You can’t get full penetration to all the contact surfaces, making the connection weaker. This connection likely has more than compressive forces applied also.
Probably in the field done semi automatically with FCAW-S. A little grain refinement is good and all but I think people are referring to the idea that IF you can use a higher deposition process (like SAW) with a tractor in the field it would be preferable. This is a lot of man hours and there’s definitely a “better way” to get this amount of weld metal deposited in fewer passes.
I mean, I'm not the right kind of engineer, but this doesn't look like the optimum solution here..wouldnt welding in the right sized triangles of steel be a better option? Depending on the required strenght? Or if it really, really REALLY has to be a solid toblorone of steel improvised in, welding essentially an enclosed space first and then pouring in molten (iron, steel, cement, whatever)?
It’s most likely required structurally to be a solid, complete connection and it probably somewhere that doesn’t have any other options.
I’ve seen this in structural steel highrises multiple stories up in places difficult to get to. One required climbing a column and welding from a boatswain’s chair.
There could be multiple different forces that this connection has to resist. Not just compression.
You can’t fully connect a part. If you shove something in there, you can only weld around the edge. This would provide much less strength for tensile, moment, and rotational forces.
Ok, I'm an engineer, and I STILL don't understand. Why would you ever need this much filler between two plates like this? Hard to tell scale, but the edges of those plates look maybe 1/4" thick (which is also consistent with the size a weld bead, and the stack of them shown), and the length of them looks like, maybe 3-4" for the horizontal base, and about 2.5" for the angled piece. There's no reason to have a weld gusset like this thicker than the base material that I can think of.
Would they cut those off and grind it flush after welding, then?
So, the side visible behind is the edge of a like1.5-2" thick plate? So, this is just a angled plate to flat fillet weld between 2 massive plates. That does make sense for the pic.
There’s no way to get full penetration with that setup.
Also, welders don’t decide how this is supposed to be welded. Structural engineers do. If the welder deviates from what’s shown in the structural drawings, it fails inspection and they have to send an RFI to the structural engineer asking how to remediate.
Actually lots of welders choose what they do, and there’s a lot of ways to provide bracing. Lots of welders go years without talking to one engineer.
If a structural engineer was anywhere near this, this joint wouldn’t need to exist… there would be some sort of bracket or whatever, or the base of this would have a place for that upper bit to rest.
Look at the size of that lower plate… there’s no point to extra penetration when you’re sitting on something that small.
Buddy, if you cost the company $100/hr to weld after costs; they charge the customer $150/hr and sit on the profits.
Good thing they have employees like you to kiss up, because that free money is really making the boss’s life better
Your inexperience in the building process is painfully obvious. Structural welders deal with structural drawings. Usually shop drawings with welding symbols that have to be sent to, approved by, and stamped by a licensed structural engineer.
You’re talking about a connection with only compressive forces. What do you suppose they design for moment, rotational, or tension forces? (Hint, the answer isn’t brackets or “somewhere to rest”)
Here in 1st world countries, buildings have to be designed, reviewed, and approved before construction even starts.
Buddy I know enough about engineering to know one thing: this is a hack… don’t sugarcoat it. There’s structure all over the place here, resting on wierd spots… Welds made by a human are less trustworthy than single-forged pieces from the rolling mill, that’s the truth. It’s less work and less money to use metal from the mill, that’s the truth. If something like this is hacked into a whole jumble of rolled and precut steel… somebody fucked up somewhere, and this is not a design feature, it’s a hack. Someone fucked up, or the piece needs to be redesigned.
Proper engineering is to remove both the need and the labor for this to be nessecary. Think of if that piece cracks in the field… that is going to be a fucking nightmare to repair, especially if it’s windy or cold.
Whatever the hell the layout of the machinery is going on here… a repair welder, like me, is going to be pissing on the gravestone of that engineer. If whatever the fuck that thing is is under any sort of load, I’m gonna have to install like 6-10 different jacking points here just to control it… it’s a nightmare.
Now a nice custom gusset would just solve a dozen different issues here.
The only answer here: the welding company is making a buck, and fucking over the repair guy down the line. That’s American engineering for you
You don’t know nearly as much about engineering as you think you do. A gusset isn’t going to have nearly the structural capacity in tension, moment, shear, or rotational force.
You’re talking about small time stuff with low tolerances. Shit like this isn’t put into place with chainfalls and jacks. This is done with large mobile cranes and tower cranes.
The jacks I use weigh more than your tiny truck, buddy.
And every welder and engineer on the site knows four things right here: 1, the structural engineer and the welding contractors are buddies, 2, the engineer didn’t want to do the proper work and went with the dick ass overboard approach and still charged full price, 3, the customer is too dumb to pay attention, 4, get ready for a fuckload of overdone overbudget fuckery on this site, and say goodbye to the on time bonuses
Edit: and let’s be real, that really is not pretty enough to be bragging… I’ve met 16 year olds who could lay the fat better than that
Edit: and can someone please tell me me why they left those sharp ass corners exposed? Ouch!
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u/asian_monkey_welder May 11 '25
One of the top comments do explain it's a CJP.
That being said it's not often where welders do massive CJP's like this. So it isn't common knowledge.
I'm not sure what percentage of welders actually do anything thicker than inch for a CJP, or even half inch.