Tip #5: Translate Structures for Engineers - Top 10 Tips - Architecture Registration Exam A.R.E.
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Tip five, you already know structures. Trust me, you already know structures. The thing that you may have some trouble with is speaking your version of structures into a world of engineer speak. That's all it is. It's not as complicated as it looks or seems. So let's give a couple little general statements about this and then I'll use an example.
It's a key thing to understand. Engineers will say things that sound like they're truths. But they're not truths. They're just simplifications.
I'm going to use a couple of terms. One is the module's elasticity E, one is the moment of inertia, I. The section module just as another example has S. Here are some examples off to the side here of the section module being calculated.
So the E module's elasticity is a term about the stress strain diagram that describes essentially how robust a material is. The module's elasticity for steel is significantly higher than it is for say wood. Wood has a pretty good module. Wood's pretty strong. It's pretty good. Steel's way stronger. It's going to have a much higher module of elasticity.
The I and the S are about shape. So the E is about material. The I and the S are about shape. So if I'm thinking about a beam that I want to have span across say 20 feet, let's say I'm putting a joist in. We have this joist go across about 20 feet. Do I went it to be tall and thin or do I want it to be flat and wide?
So if I have a higher I, the moment of inertia, that's going to mean that I have more material farther away from the central axis. It doesn't mean that it's stronger material. I've got balsa wood that has a very high moment of inertia. It doesn't mean it's going to be strong because the wood itself has to be strong.
You realize a bunch of the time you keep stumbling across the same groupings of pieces of information. So why not just call them S and make a list of them? You can look it up in a book, instead of finding all of it. Just look it up and there it is. It's just a way to simplify the world. Nothing complicated. E is about material. I and S about shape. So let's think about that for a second.
So here's one crazy looking formula. Triangle means Delta, change. So that's talking about the deflection. 5WL to the 4th over 384 EI. That is completely nutty looking. How can you know what the hell that's supposed to mean? You know what it means.
How much would that happen? Well, that's what we're trying to figure out here. That's the Delta. That's the change.
So we look at it, the 5 and the 384 are just constants. Who cares about them? They're there. It doesn't matter. You don't need to worry about those. The W that's the weight. The L that's the length of that beam. The E and the I we just talked about. That's the module's elasticity and the moment of inertia. So let's say we have this joist and I'm trying to decide between doing it out of wood or steel.
Are we going to make this joist out of wood or steel? Everything else is the same. We have a set situation. We have a certain length. We have a certain load in the design expectation load that we're expecting. So there's a certain idea of this design concept that we're thinking about and now the question is do we put a wood beam there or steel beam?
What's going to happen to the E if we use steel instead of wood? It's going to go way up. Steel's much more robust from the module of elasticity standpoint than the wood is. Even Douglas fir which is a very good wood is going to have a much lower E than the steel would be. So okay you look at that formula what does that tell us?
That tells us that the denominator, the lower number is going to get much bigger therefore the overall fraction will be a smaller number therefore if we use steel, it's telling us that we're going to have less deflection because it's steel than if it was wood. That was something you knew already. That's something now that you look at that diagram, that formula, you can tell that's what it's saying to you.
Use wood instead that lower denominator goes up. The Delta changes therefore that means there's more deflection. This is what you know. Okay let's say its wood. Let's say we chose Douglas fir and we're doing it out of the wood and just like we talked about a minute ago we say "All right, are we going to do it vertically or are we going to do it like a board?"
So we have two choices. One is that we're going to use it vertically in section and the other one is that we're going use it like a board in section. Well, that's about shape. The farther away we said that I want to span across. I want to get the meat of the material farther away from the central axis of whatever it is my spanning material is. So there's the central axis for that one.
So look it up sine, cosine tangent.