 Alright, as promised, an example problem on a bolted connection in shear and tension. If you remember, we're using an interaction equation between the shear capacity extracted and the tension capacity extracted. What we've decided to do for no reason other than it's as good as any, we will first put our shear loads on here, check out bearing stresses, check out the stress in the bolt in shear, make sure that the bolts are okay for shear. We'll probably hope that they're away from how much we could have in shear because we want something left over for tension. In an analysis problem, that's not a problem because what it is is what it is. If this 54 kips is bigger than your bolts can handle in shear, you're off the charts anyway, so you've got to quit immediately. In a design situation, you've got to just pick a number of bolts where you leave some left over capacity after you admit to the shear part and hope the tension that's left over is acceptable. And there are ways to get a handle on where to start. So the case is we have a W14x90 made out of A992 steel. We have bolted to it an A36 bracket, probably a T-section. Got four bolts in it subject to pulling the little plugs out of the bracket or crushing the steel in the bracket or perhaps doing the same thing in the wide flange. One thing's for sure, the T-section is a 10.5 by 31, it's given. You go look up the thickness of that item's flange, it's 0.615 inches and it's bearing against a 58 ksi steel because it's A36. The W14x90 is out of A992 steel and if you check its flange, which this connection is attached to, it's thicker and the steel is stronger. So I don't have to worry about which one to check, whether I should check the wide flange or if I want to check the T-section. The T-section's guaranteed to control all bearing and stuff like that. So to compute the nominal bearing strength, the flange and the T, I have two choices, I have 2.4 DTF subultimate and I have that other thing depending on the length of the plug in front. Looks like he's not going to bother with that. And I say, you better go check those little plugs, make sure they don't pull out. He says they won't pull out. I said, how do you know? He says, I'm going to design this thing and when you tell me the little plug is going to pull out, I'm going to make the thing longer so it doesn't pull out. But he's saying right off the front, assume that the crushing strength, which you can't do anything about it, it crushes when it's going to crush. You can always make the plug longer. You can always make the plug long enough so that it crushes first. And he says that right here, assume all spacing and edge distance requirements are satisfied, including those necessary to use the maximum nominal strength in bearing, which is crushing. So then you get 2.4, diameter to the bolt, thickness of the plate times F sub u, and you get 74 kips per bolt. That's the crushing bearing. It's a bearing type failure. Plug shear is a bearing type failure. Crushing is a bearing type failure. Nominal supply available. If you want all the words, that's all of them I know that relate to this guy right there. Now, to prove out these numbers that we're already starting to see, I'm just going to go ahead and throw in all the pages having to do with bolts that you probably will refer to. First off, if you have a slip critical connection, we said that the nominal load was a coefficient of friction. D sub u, what was d sub u? What was d sub u? 1.13, what was it for? It was because every time you tighten a bolt to the minimum required, you always about have to give me more, and they know you're going to give me more. And so they let you take into account what you're really going to put in there. 1.13 times the tension in the bolt, minimum required out of a table. Times a filler factor, which ours will always be one, times the tension in the bolt, times the number of shearing planes. Now, this is only true if you go look at your little summary of answers. If the bolt shears at 60 kips, then the bolt will shear at 60 kips, and the bolt will shear at 60, and it'll shear at 60, and it'll shear at 60, and it'll shear at 60. And if the little plug pulls out at 80, and the little plug pulls out at 80, and the little plug pulls out 40, well, then this is no longer true. I mean, it's true for any one bolt, but it's not true for all the bolts, because something happened at this hole to not get the shear strength or the slip strength that we're talking about. Still has to be checked for bearing. We surprisingly get a resistance factor of 100%, not too much variation found in a test. Filler factor was a one for us. If you also put tension on the connection, which we are just now doing, then the planes that you were planning on being compressed to this number on the previous page will not be available, because you're going to pull them open a little bit, then you must reduce this force in between here, and you reduce it by 1 minus T sub u, D sub u, T sub b, N sub b. T sub u is the required, I don't like the word required. I guess it's okay. I mean, I like, I see it better if I say it's applied. The force is applied. And so, yes, that means it's required, but that's like one step down a road to me. This is, you take this number right there, that's this number. N sub b is the number of bolts that you're putting in the connection. D sub u is the same. You reduce your slip capability by this amount. Bearing strength, 0.75 for resistance factor. You have a plug shear strength listed. You have a crush shear strength listed. You have other cases too, which we don't get into. If you get out, you'll probably want to read these things. Long slotted hold. Do you have any long slotted holds? Wow, saw one the other day. Maybe I better use this instead. Tables on the pretension in the bolts. Group A, group B, bolt size, tension to be installed in the bolt. Go back to our problem. The nominal shear strength of the bolts, we already have the nominal bearing strength now. Size of the bolt is that big. Whether it's threaded or not, it's that big. If it is threaded, they'll knock your permitted shear stress down to account for the fact that you cut it at the threads. Your nominal capacity is our nominal shear stress area of the bolt. Shear stress changed since I printed out all these beautiful pictures. So I had to change it to 54. And let's see where that 54 came from. It came right there. It was a group A bolt. Threads were not excluded from the shear plane. Nominal shear strength right off of here. You'll notice that nominal shear strength doesn't say it, but he means in the absence of tension. And he doesn't really talk about it on the tension stress here, but he means this is how much tension you can have in the absence of shear. You get them both on there, and you can't have both those numbers. The area for threads cut, threads not cut, threads cut, threads not cut, same area. Pi D squared over 4, where D is the diameter of the shank. Those are designated A325. Shear plane includes the threads. Threads are excluded, included, excluded. So there's where the 54 came from. There's the cross sectional area of the shank. 32.5 kips per bolt is your shear nominal supply. Going back to what the picture looks like, I think we had a 60 kip load. No, we didn't, we had a 60 kip load, but 15 of it was dead and 45 was live. 1.2 dead plus 1.6 live gives us 90 kips of load factored on the connection. Three-fifths of it goes down because three-fifths of it's slope goes down. Three-fifths of 90 is 54 kips of shear. And four-fifths goes horizontal, so four-fifths of 90 is a tension load. We're going to do shear first. It's arbitrary, we're going to start with tension first and then work over and see how much shear is left for us. But instead, we're going to do shearing stresses first. Then if there's something left over for us in tension, then we'll go see what if the tension capacity is big enough left for us. Total shear or bearing load is three-fifths of 90, that's the 54 kips you see down. Shear bearing force per bolt, 54 over 4 bolts have been suggested, this is an analysis problem. 13.5 kips per bolt requested. The design bearing strength was we had 74.91 off the previous page nominal. We're going to have to go ahead and put the fee in there to see what's permitted. This is the bearing permitted, fee times are nominal, 56.2 kips, well over what you need. Design shear strength of the bolts is the bolts were good for 32.5 kips per bolt. And they get a 0.75 fee on them, resistance factor, so they're good for 24 out of the bearing and the shear. This one obviously controls, but it's still above the request of 13.5 kips per bolt. 13.5 kips per bolt. So we're okay so far. Incidentally, the design shear strength is 24 and you're only asking for 13, so you've left me some room here in the shear. You haven't used up all the shear. If your number's worked out and this said 24.4 is equal to the 24.4 kips requested, then I'd say don't bother with any tension. Or yeah, you can still put a little tension because you remember this curve, it actually could, you could still get tension. But you shouldn't expect too much. This is the curve that we're using. It comes in at F sub nominal in tension for the kind of bolt you're using. In this case, it comes in at 90. Here is the nominal in shear, came in at 54. Let's see where those numbers came from. There was your 54. In the absence of tension, you get this much shear. In the absence of shear, you get 90 tension. So there's our two numbers. And we draw a straight line instead of an ellipse using the same method that the specs use. You can't go out here because you would exceed how much you're going to have just by shear alone. You can't go up here because you would exceed the maximum permitted. Even if you just use a little shear, you can't go up there. So that'll have to be checked every time. So now we work on our tension side of the connection. Tension force was four-fifths of 90. That was your 72. Tension force per bolt is, ask for 72 over four bolts. 18 kips per bolt is your request. That's T sub ultimate request. Determine how much remaining nominal available tensile stress for you after shear is accounted for. AISC equation J33A says the amount of tension stress nominal left for you, that's the little prime, is equal to 1.3 times the table value, the nominal tensile full blast no shear, minus the nominal tension full blast no shear, divided by phi times the nominal value full blast for shear, times F sub Rv. Pretty ugly there, here's a better one, F sub Rv. F sub Rv is the actual shear stress that you put in the bolt. And even if you use this equation, this equation will sometimes go nuts and go up in here. So you've got to check that when you get how much you can have, he doesn't tell you more than 90, less than full blast nominal tension with no shear. He tells you what all the terms are. F sub nominal tension, nominal tension stress, they also call it strength. I wish they wouldn't switch around like that. I wish they would call it stress or strength. The truth is it is a stress. In other words, you look at any of these things like F sub NT, I don't see one off hand, we'll get one in a minute here, but they are actually KSI. And that is a strength, it's a strength in KSI, but I like this right here where it says stress. It is the tensile stress permitted in the absence of shear, 90. Nominal shear stress, including the phi, in the absence of tension. Excuse me, not including the phi, that's nominal. So our F sub RV that we asked for, we took out of the connection already, was the load over area. No fees, no this, no that, it's just an ultimate request divided by the area of the boat. You have already used up 22.5 KSI of the shear capacity or the overall capacity of the connection. Now I've got notes everywhere here, what do these notes say? This is the page number that you'll find this equation on. It's on page 16.1, that's 25, it's on our 429D, back a few pages. It is J33A is where you're going to get some of these numbers from, that's the table. I showed you my preferred version of this, I don't know, it just looks like less number work. F sub NT prime is equal to F sub NT taken out of both terms onto 1.3 minus your requested already removed capacity due to shear, divided by phi times FNV, the nominal shear permitted with no tension right out of this table on this page. Resist stuff, these are for A325 boats, they are table nominal strengths on page 16.1-120 and also on this page coming up in a minute. This is already used up, that's what that number means, F sub V, F sub the symbology changed since last time. F sub RB, and it's just flat O load over area, your load, your V sub U, your V sub U over the area. Then we can solve for how much tension is left for you, 1.3 times the table value minus the tension table value divided by 0.75 is our phi. Times the table value for shear, changed since last time I taught this, times how much did you actually already take out. I saw your hand in the cookie jar, there are fewer cookies in there now than there were before, how many cookies are left for me is equal to 67.1. Now since that's less than the maximum number in the table, this is acceptable to proceed, as you can still proceed. But if this number said 97.1, then you would say how much is left for me is 90. F sub NT is the nominal tensile stress left for you after accounting for the presence of shear, if it's okay to slip. Now slip is a different thing, this one he didn't mention that it couldn't slip, so here are our tables continuing. The nominal tensile strength remaining for you was the permitted stress for you. See he's using strength in two cases, he's using strength as if it were a stress sometimes and it is a strength and he's using it sometimes for a load. So the nominal tensile force, the reason I know it's a force, it has a stress times an area. The nominal tensile force remaining for you due to the tensile stress that's left for you is the 67.1 left for you times the cross sectional area of the boat and that's equal to 40.4 kips per boat. That's the nominal force intention remaining for you per boat. So our only question is how much did you ask versus how much is left for you? The available, this is the nominal, the available will be 0.75 times that number, that's 30.3 kips per boat. That's more than 18 kips per boat is the tension load you asked for, it's okay. So the connection is adequate as a bearing type connection. He says look I haven't included prying on this thing, so not to obscure, it's just the prying thing adds one more complexity to it. Obviously, you've got enough complexity just in all of this stuff, he wants you to get that down. Now the second thing was, the boss came in and says that's slip critical, isn't it? I say no it's not slip critical, what he means is it's slip critical. He says well it's supposed to say slip critical, I said well you look the specs right, he didn't say slip critical, he says well okay, go do it because I know it's slip critical. Okay, is it supposed to be slip critical? No, not supposed to be slip critical? Had a 50-50 chance there, I have some sad news for you though. It is supposed to be slip critical, I mean I just got bawled out because it wasn't slip critical and I did the whole thing, it's not slip critical. I didn't really lose any time because even if it's slip critical it still has to be capable of a bearing type connection. So all right, I'll get right on it, he says have it done before the morning, he says it's already nine o'clock at night, yeah. From part A, the shear bearing intensive strengths are satisfactory from equation J3-4 and I know dang good and well that Steinhub was going to ask me where that sucker came from. Oh here it is right here, came from page 16.1-126 and they should be here, I try and get them all there. I've got a copy on page 431f so you don't have to dig out your manual. How much capacity you're going to have, coefficient of friction, d sub u, I forget, what's d sub u? 1.13, there you go, I don't even care if you know why as long as you always know it's 1.13 because you get 13 percent, 13 percent more tension in the bolts right across the board every time you tighten them up properly. Times the filler factor, times the tension in the bolt out of a table, times the, this should be, was this little in in the previous thing, I don't know whether we're using big in or little in but that's the number of slip planes. Here I say do we still have 54 kips of slip capacity, I guess that's really what we're asking, see if we still have 54. From table J31 prescribed tension, that table 3-1 prescribed tension, is that 3-1? From table 3-1 the prescribed, it's 39 kips, oh that's not the tension is it? This is, that's right, that's that pre-tension table. So you'd have to go to the pre-tension table and find out what it says, he says 39 kips I gotta check on it, that's two of us that say that, that's the majority. So on this page right here, assuming class A surfaces which you and surfaces, which you and I always do, we get a 0.3, which we always get, and for four bolts you crank out all the numbers coefficient of friction, how much higher will you really put tension in the bolts, what kind of fillers do you have, either none or one or six that are bolted down so they don't slip around, times the tension of the bolts at 39 kips, one shear surface times four bolts 52.9 kips, then fee times that, I was gonna say hey what happened it's still the same, that's right, our fee was a one for slip wasn't it, there's so little variation in there that they say you do not need to have a 0.9, a 0.75, 100%. Now then he says but there are some tensile loads on there, I say well yeah you know no big deal, he says I think it is a big deal, you are opening up that compressed pair of plates, yeah you're right, he says do you know how much you must reduce your capacity 52.9, I say I think it's in the book, he says go dig it out, one minus the requested load of 72 kips, applied tension load reduces the pressure between the t and the flange, divided by 1.13 times 39 kips for bolt times four bolts, basically you put this number into the bolts when you started, now all you're doing is you're taking it back out, therefore you only get about 60% of the slip capacity you had before, are you planning on, therefore case of SC, parentheses 59, 2.9, okay okay you say multiply the, multiply the value you get for case of SC times the 52.9 without accounting for the fact that you opened up the plates it gives you 31.3, darn that's sad isn't it, didn't work, you were asking for 52 kips of shear load request capacity, you only got 31.3, go back and really make sure he's not just kidding us, no we really did, we asked for 54, so how are we going to fix that? How? Bigger bolts? Bigger bolts would work, I was thinking more bolts, I don't know why bigger bolts would work, of course bigger bolts will also cause wider holes and things, stuff like that, but more bolts is a problem also, but we do got to do something, that's no choice. Now let's just say that instead of using four bolts to try and get this thing up, so there's more pressure between the plates, I do that with more bolts, then when you put the 72 kips of tension on there, it comes down, it doesn't reduce it so badly that I don't get my 54 capacity, I had a reason for going there, but I don't remember what it was, maybe I'll think of it in a minute, I was going to use more bolts, oh I know what it was, after I used six bolts in there then I got to go back and do all of this bearing stuff and shear stress and it's right, no why not, it worked in the first place, it worked with just four bolts in bearing, so if you got to add two more bolts to make it work in slip, you don't have to go back and check it with the six bolts in bearing, you know it'll work then and so in effect you're through, see it was a good question, I just couldn't remember what it was. All right, now then we're going to design, let me see what this tail in, where did we find out the bad news, here's where we found out the bad news, no that one was okay, this was in tension, this was in tension, this was in tension, this was in tension, oh this was slip critical, here we go, and we found out it wasn't going to work as a slip critical connection and he lets it go with that, somebody has to go back and stick some more bolts in there, now then the specs on tension, high strength bolts in slip critical, there's our equation on page 16.1-126 for efficient of friction, for fillers, you know like we already had these pages and how much our slip critical thing gets reduced, yes it's already covered, okay, these are the pages out of your book but they don't have pretty pictures on them, you do have an error in your book, this should be 52.88 kips, oh here it is right here, so it's a pretty easy problem to see because one times the old number isn't this, loud stress, loud stress, loud stress, all right, now then, design, a concentrically loaded connection, they call that a simple connection, it is a connection like the one you and I just did where the load runs through the centroid of the connection, through the centroid of the group of bolts, subjected to a service load of 50 shear, 100 kips in tension, the loads are 25 dead, 75 live percent, fasteners are in single shear, bearing strength will be controlled by 5-16 inch thick part, made out of A36 steel, sum all spacing edge distances are okay, including the maximum edge distances, you can have full crushing strength, we're going to make the little plugs long enough so they don't control, determine the required number of three-quarter inch group A bolts for the following cases, bearing type connection, I know how to do that with threads in the planar shear, no problem, slip critical connection with the threads in the planar shear as before, yep, in the planar shear, yeah, all contact surfaces clean, mill scale, means coefficient of friction 0.3, it says consider to be a preliminary design so you don't have to include the prying action, here's our old friend, this is your nominal strength comes from these pages and these our pages, got a top out at 90, gonna design so that we start out at 54 and see what we got left, if you're designed or if you ever try and pick a number bigger than 54 you can't even get started, here's your loading on this particular bolt, 150 kips of tension, 75 kips of shear, factor loads, 25 percent of the load he gave us was dead, that's 1.2 dead, 25 percent, 75 percent of it was live and so 1.6 times 75 percent of this to get our factor load in shear and in tension, so here we go for bearing type connection threads in the plane, he says assume the tension controls, well I'm not used to you, assume tension controls and he says yeah well you know you used to designing things either, he says if you'll tell me if you'll guess the number of bolts like you did in the previous problem then I can start and I'll find out how much shear is really in the bolts and then I'll tell you how much is left for you in tension, but this is a design problem where the number of bolts is unknown, I said you just said they were three-quarter inch bolts, he says the number listen listen the number is unknown, ah okay okay so he says assume tension controls, truth the matter is when you get a little further in here you find out he's assuming tension and shear controlled at the same time, well I don't think that's real likely, he says probably not, I said okay I'm going to try and sell this to some people, some students, he said tell them it's a starting point, they don't have to use it, if they'd rather they can just guess 16 bolts, we don't care and if it's good they'll you know then knock it down to 10 or if it's not good they'll build it up to 20 and in about a week they'll be through, I said okay your way is sounding better all the time, he says you decided that F sub NT nominal tension left for you in tension is 1.3 F sub NT that's equation J33A minus table value net tension nominal tension table value permitted maximum nominal shear in the absence of tension times V times the true shear request but of course less than that, I said he says okay now let's go ahead and put in our numbers for this bolt okay F sub NT was 90 that was this guy up at the top go ahead and put in the 54 at the same time there's the 90 there's the 54 there's the 0.75 and be less than 90 this works out 117 minus 2.22 times F sub NV calculator number right here but it's got to be less than 90 okay he says F sub NV times all these numbers so I can go ahead and get allowed numbers here is 0.75 across the board so he multiplies 0.75 times this number in a parentheses less than 0.75 of that and he goes ahead and cranks out the numbers he says this is how much permitted not nominal this is now how much permitted stress you can have in tension for your case 87.75 minus 1.667 times F sub NT but it got to be less than that then here he comes in here and here's where he really says why don't we just assume that this number is 150 the request divided by the area of the bolts I say okay in other words you're assuming that the tension really controlled well he says kind of because at the same time why don't we just go ahead and assume that the bolt's in shear also failed with your load divided by some of the bolts or not necessarily failed but that is you set your requested stress equal to the tension available and you set your requested equal to what's permitted for you in the shear in this equation say okay he says look it's a place to start nobody says it's going to be perfect half the time you won't have enough bolts half the time you'll have too many bolts but it's one thing's for sure at least it gives you a point we found is good to start all right so he's going to take 150 over some of the area of the bolts that's the true shear stress in the in the bolt and he's going to put that right here is equal to 87.75 minus 1.1767 times the true shear stress in the bolts the load of 75 kips divided by the area of the bolts I say I see one nice thing however you got it that equation only has one unknown he says do you notice what it is uh see area of the bolts he says isn't that nifty I say well let's see how it works out therefore you solve for multiply everything through here by the sum of all the area of the bolts and it only appears here and you solve for that you need 3.134 square inches of steel in the bolts since the area of one bolt is pi d squared over four and I can tell you that you need there was that minimum bolt pretension table and I can tell you that you need uh here's your how much shear stress we put in those uh permitted numbers you need here's the tension strength 0.75 here's that equation again what's the thought I lost those pages oh come on here we go and therefore the number of bolts required is you need that much total you get that much per bolt you need eight bolts even if it was 6.8 you wouldn't use seven bolts you know you're going to use them in pairs probably maybe it's first trial so we're going to try eight bolts first we check the upper limit on f sub nt prime the upper limit is just meaning does the case we're trying here exceed the 90 ksi to begin with or whatever it is when it's factored the actual loads give the actual shear stress requested they have to be less than permitted f sub n f per bolt shear is actually 75 over our new area of the bolts number of bolts you're going to be putting 22.22 ksi in my bolts it has to be less than the table value with a fee on it so he hasn't really done it here he just says I don't know what he's going to do with it later but me I can't resist if I'm going to have that much shear stress in the bolts really I'd like to know how that compares with how much I have available 40.5 ksi so I'm okay on shear not only that there's some left over which I can probably use on the tension side of the equation check the tensile left for you this is the stress nominal tension not yet factored for you 1.17 minus I don't know if this is still in your book or not it's just a mistake minus in fact it used to be 2.5 when I was younger minus 2.222 times f sub requested in shear 21.22 there's your request there's your request there's your request is equal to 69.8 and you have now proven to me that you are not going above the max permitted now one thing he's got he just flat forgot he forgot to check tension stress in the bolts down here he got back on see this is tension left for you nominal this just says you didn't go above 60 this doesn't say this number will work in your bolt and he accidentally got back on shear and I think he just forgot to do that so now he's going to check the shear in the bolts I'm not sure oh I know why he rechecked it because I'm the one who checked it up here had you checked it right here you wouldn't need to recheck it here here I checked stresses to make sure the stressors were okay down here all he does is multiply times the area of the bolt how many bolts there are and prove that the loads are okay well if the stresses are okay the loads have to be okay so here's his check phi times f sub n v permitted times area bolt times number of bolts in shear that was three quarters his fee 54 was shear 44 18 was the area of the bolt there's eight of them you have a 143 capacity that's bigger than 75 kips request that's that's definitely going to be the case you'll notice that the numbers even look like they're about in the same proportion they ought to be then he says I'm going to check the crushing the check bearing he's checking the crushing so he goes through the plate crushing thing and he checks 2.4 diameter of the bolt thickness of the plate f sub u eight bolts bearing against the plate 196 greater than that 75 kip shear load not the 150 tension uh i guess that's because on a lot of exams i run across people to check that against the tension load it's only the shear load the tension load causes no bearing only the shear load causes bearing and a problem they forgot to check the tension so here's the check for tension has not yet and must still check tensile stress to make sure the actual tensile stress is smaller than how much we left on the table for you here's your actual request load over area stress requested in tension 150 kips of tension divided by eight bolts area of the bolts 42.44 and we left 69.8 on the table for you so now i'm happy it's good but had this number right here come out 70.6 still less than 90 70.6 is not smaller than what was left for you and the connection would not be good now you can do the same thing we did on the previous page you can also check the loads but it's not required if the stress is okay the loads have to be okay so r sub u t less than phi r sub nominal that's phi f prime a b and b blah blah blah 185 kips you only asked me 150 it's good enough and i have no idea oh i see well 75 kips was our shear load so that does look like our t and evidently this is where we were trying to say how you're going to make sure that the plugs don't pull out you know here's how i make sure the plugs don't pull out there you go those plugs not going to pull out it's an angle of course looks like this and if it's an angle it would be subject to what very good block shear okay we don't cover any of that all right a brief introduction to welded connections bolted connections are nice but they how many minutes i got left five i saw you checking bolted connections are nice but they do put holes in your plate you're right five welding is but the nice thing about bolts is they can be done by unskilled people you give a guy a drill or lady a drill you know and they can usually drill a reasonable hole in something and put it in the pretty much the right place a lot of that's done by machines anyway and then they can put it together pretty well because they'll have an impact wrench and it'll turn off with the right torque or uh juice will squirt out from underneath the washer or the torque wrench will go something like that tell you it's time to quit the the putting the holes in the plates is the biggest problem welding the biggest problem is you got to have somebody who knows their business you can really cause a lot of grief i was on a case actually in Beaumont the name of the place was lee engineering terrible and the welder told us that uh he'd put a weld on there and then he would put a kind of a thing it called it a cap and it was called a surface something well the people came by and they thought that the weld was that big but if you only put this much weld in there and then you know kind of covered it up it looked like it was the right size but it's not and it had a collapse so you've got somebody who's not careful doesn't care really wants to get home not certified they can mesh up pretty good they don't know too expensive wow cost of fortune this is an offshore drilling rig we just bring it in the lab right have to cut it up to get it in the lab and x-ray it then we have to weld it back together and we have to bring it back in to x-ray the welds you know kind of kind of is necessary but generally speaking no we depend on certification the way it works you this guy's got a plus charge this guy's got a minus charge you get it close enough an arc jumps across there it melts off metal off of the electrode there's stuff on the outside of it when it grows off because of the heat it's a gas the gas keeps the metal from getting oxygen on it till it gets cool and it just makes one part out of the whole thing excuse me one way you can do them they're called fillet wells they look kind of like this they're not permitted to really do this one thing you also won't let them do is you won't let them burn the corner off on a reasonably thick plate because then you don't know if this is the size of the weld or this is the size of the weld read that material there's groove wells there's complete penetration wells there's plug wells where you weld in the plug the strength of the well depends on the strength of the and it also depends on the strength of the electrode the metal they make you use a matching well well material a well a rod that matches well to the plate their basic strength is force times area what else is new here's your here's the size of the weld whether it looks like that or not you don't normally count it the root is down in here come on in come on in it's okay or if it's people avoid my class no matter what even if they don't know me and the strength of that weld right there will be based on its throat dimension that'll be w times the cosine of 45 degrees and how long it is and when you pull on this weld side and when you pull on that side you get that much strength it's kind of interesting if you have the weld and you pull up on this plate and you pull down on this plate you get the same strength well not maybe not really but kind of looks that way there are there are corrections to that see you next time