Concrete: 3. Cip Concrete Reinforcing

Concrete: 3. Cip Concrete Reinforcing

Concrete: 3. Cip Concrete Reinforcing - Full TranscriptionI'm sorry, I just looked at the recording I made for four work. It was 30 minutes. I'm so embarrassed. I keep talking. Anyway, I hope you're benefiting from all of this. We're going to talk about reinforcing next. Looking at this picture here, I see a little bit more reinforcing above the columns. This is a plan view. So I'm assuming that this is a flat slab, right? When they reinforce around the column, it's going to be a flat slab. And the worry, of course, is punching shear. So here we go. Let's support this beam here with some kind of column and over here. Then the top rebars are in compression and the bottom rebars are in tension. The stirrups, on the other hand, are doing shear. These are the stirrups and they're doing shear. And shear is high at the support. Therefore, they might be even closer than shown. Versus at mid-span, the moment is high. Therefore, the rebars need to step up and pick up that moment. As we said in the previous video, there's space ties versus spiral tie. The space ties could be rectangular. they could be round, they could be whatever. Here's some formwork for this template, not a formwork for tying the rebars for this round column. It looks like the rebars of this column on the far right are bent, which means this is the final floor. Otherwise, they'd keep them sticking up and they would bend them as we saw in the formwork video. These are the ties they use to tie the rebars. That's what this one is. And they have a pigtail twister that makes their life a lot easier and ties them quickly. This is the welded wire fabric or welded wire mesh. And it's basically for slab on grade or for non-structural. It is for thermal resistance against cracks, so the slab doesn't crack. Now there's reinforcing at a closer interval. This is wire. It's not rebar. So it's there for thermal purposes. Very good. what else? Oh, here's some rebar. Let's look at this one. A number three rebar is three-eighths of an inch. A number four rebar is four-eighths of an inch. These two are used for stirrups or for temperature reinforcing in a slab. Then number 5 through number 10, which is 10 over 8 or 7 over 8. It's the diameter of the bar divided by 8. The number divided by 8 is the diameter. Then these are regular rebars used for beams and columns. And then there's an 11, there's a 14 that is not on this chart, and there's also an 18. These are the heavy hitters, big skyscrapers, bridges, etc. They use 11, 14, and 18. And a number 18 divided by 8 is 2 1⁄4 inches. That's pretty hefty. When you see a rebar like this, if it has a straight line, a rib that is straight versus these ribs that are helical, the straight line says, I am a grade 60 rebar. Grade 60 is basically, you will recognize it because of these ribs. So I'm looking at this one, and it says, where is it? I didn't look at it before I started. Anyway, here's a tag. This is a number four, and its length is 20 inches. Its grade is grade 60. Versus this other one, it's a number 11. It's a grade 60. It comes tagged. So there's three of them. They're 41 feet and 5 inches. And the way you measure the diameter is basically on the end of the rebar. In this case, it looks like an inch and a quarter, inch and a quarter, which says I am a number 10. That's inch and a quarter. This one, too, is from here to here. That one looks like it's also a number 10. That's a quarter inch, inch and a quarter, which is a number 10. Yeah, this is an epoxy. coated rebar. It is used in infrastructure, in bridges and roads. You can see here the top layer is epoxy coated, but the bottom layer is not epoxy coated, it's regular, because they're going to have to throw road salts that are corrosive to rebar. So we'll use epoxy coated on the top, on the bottom, we're not going to get road salts, so we don't need to. This is an interesting case that I saw once. It was a parking garage and they had these epoxy coated stirrups only at the height of the bumper of a car versus above and below its regular ties. And the reason is if a car bumps into this column, at least if the rebar is exposed, at least it's epoxy coated so it doesn't corrode. Very good. So that is introduction to the rebar. These are, oh, I didn't say that, did I? Okay, let me go back quickly and say in a beam, this one is called a stirrup. But in a column, it's the same member, but it's called a tie. So, ties are stirrups for columns. And stirrups are ties for beams. Same thing. Okay. So, let's look at this one. Here's some stirrups and I'd like to show you, I like this because I took my students on a field trip to Aprica. Here you can see how the stirrup is in place. They have this attached to the computer and I see two bars, number three or number four. And this machine bends them. versus this other machine over on the left. They're trying to make a U out of a rebar, and this machine bends it into place. They take it, they insert it in the formwork, and they pour. Very good. So back here. So I can look at these three examples, and I can say that this one is an intermediate floor. there's something there's going to be another pour coming up and we can see that because the rebar of the column is bent so that the next cage comes in and sits on that bend and the next floor goes up versus this set of rebars is bent therefore that's it this is a top floor our roof this one we talked about earlier. So this one is continuing, but then these bent bars are going to tie in monolithically to the floor. So splicing, let's talk about splicing. Splicing is basically the rebar that comes from the previous pore here, bottom left in this picture. There is some dowels. That's what these are. They're coming out of the previous pour. They're called dowels. And then they start to do the rebar for the next level. And they attach it to, they splice it to the existing dowels. And now when they pour, it's monolithic. Same thing with columns. I see short, right here, I see short bars coming from the previous pour, and then they splice, they built a column cage, and then they splice it to the existing. That's what these are going to be. If there's another pour, you can see rebar sticking out from previous pour, and then they splice to them. Same thing in the foundation. I see, let me see where they are so that I don't confuse you. Let me try to follow it. This one goes here. I'm not sure where it stops. It stops there, let's say. This one goes here, stops there. So these are the dowels that are going to come out of this pour. They'll pour up to a certain level, up to the level of these pieces of wood. That's what that green paint is. It's telling them to what level to pour. And then they'll come back and they'll bring more bars to the wall, and then they'll tie it to the dowels and now it's monolithic. We can see the same here. A short column dowel and we'll pour up to somewhere here. These are for them to walk on and then there's the paint. They're going to pour up to this level and leave these sticking out so that they can come back and splice. Very good. Now in this case, what they did here was they threaded this number 11 rebar, which is crazy. It's huge. They threaded it, and it looks like it's very congested in here. There's too much rebar for the size gravel and the concrete to totally embed and envelop the rebar. So this case, what they're doing is a mechanical splice, which is basically, this is the rebar, and this is the other rebar, and they overlap them with this mechanical connector, a coupling. That way, they don't have to put two layers. That way, they don't have to splice like this. Oops. They don't have to splice and use up that much width. They will splice like this and splice and then put the mechanical coupler on there. So, whenever space is tight, mechanical couplers do the job. So, back to cover. Three inches in the ground, two inches on the envelope, inch and a half on the interior, or three-quarter inch on the slab. There's different height chairs to give you the cover needed. And then there's these bolsters that we said earlier that can be used also to get a three-quarter inch, for example, cover in a slab. Slabs on grade are to have a reinforcement in the top third of the thickness because they're going to walk on it and it could have some heaving. So it's going in the top third. But here are some examples of not enough cover. That the rebar showed up. That one, the tie showed up. Here they didn't land on the column. It's terrible. Once the rebar is exposed, it corrodes and there's no saying what will happen. Here, the bottom of this bridge in Milwaukee. So it's exposed. It's very dangerous. I'm sure they went in and did something to it. This was many years ago. This is an example of bad craftsmanship where we can see the bolsters here, but the concrete didn't go around the rebar on the bottom, which is a big old problem. We see a support jack here. And then they went in and patched it. I mean, I have no idea, frankly. Whatever. Master Emaco, they patched it. Move on. So reinforcing, of course, is also used for post-tension tendons that are placed inside of plastic sheaths. And there is grease around the tendon. And there is a video about post-tension. but just as a preview of that. I'm talking about it here. I see in this image here, there's a lot of these shear studs. It's called a stud rail. And they're going crazy here. They're putting them in this direction, in this direction, in this direction, and in that direction. It's around the column, and there is no beam. That's why these extra stud rails, because we're not dropping down in depth. We're keeping it either a flat plate, in this case a flat plate, or a flat slab, and we have to reinforce over the column against punching shear. Also, in pre-tensioning of pre-cast members, you will see a wire in there, a tendon, that is pre-tensioned. And then the concrete is poured. Then they cut it and it makes the camber. We'll talk about all these things. Here we can see the wire. They're pouring walls and they'll put insulation in them, pre-cast walls. It's the only way to get insulation in concrete is to pour it flat. You pour a little bit of concrete, then you put the insulation, then you continue pouring. Because it's very difficult to do that on site. So this is in a factory. It's a lot easier to see. This is the bulkhead where the cables or the tendons are locked. Then they pulled from the other side. Very good. One more thing. If you think of the formwork of this double T, it is chamfered here, and then it goes down in the stem. It's chamfered, and it goes down in the stem. And the reason is simple. I have to be able to pull up the double T from the form. That's when you chamfer. The double T has a stem that is tapered so that it can come out clean. Okay. I hope I didn't break the time limit. Bye-bye.