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Hello Azawi české fam, it's Josh.

And for this week's stuff you should know Selex. I've chosen bridges. Nature abhors them, which we released back in June of 2015 and it's a pretty good one. It's got a lot of engineering, believe it or not, but it's not like the I glazy kind. It's like the oh my God, this is amazingly fascinating kind. I hope you feel that way at least. And I'll bet you will. So enjoy bridges. Nature abhors them starting.

Welcome to Stuff You Should Know. A production of I Heart Radio. Hey, and welcome to the podcast, I'm Josh Clark and Charles W. Chuck Bright with Gerri rolling with me. Josh Clark, this is stuff you should know featuring Josh Clark, but say you never introduce yourself. And then he did it twice. Three times. Uh oh, yeah. You always introduce. Yeah. But you never say your last name. I think that's what struck me.

No, I say I'm Josh Clark. Yeah, every time I should listen to these sometimes. Yeah, that explains the glazed over look in your eyes whenever we start.

Um, bridges. Yeah.

That your intro. Yep. I like them. Maybe we can add like a scat drummer.

On top of that, we have that kind of when we're doing, uh, listener mail is a little bit at the time.

Yeah. Well that's not scat drumming I would say that's more of a shuffle. Hmm. Scat like.

Yeah. Like that. Yeah. You should get Hodgeman the scat for you sometime. He's got a lot of Bourdos going on when he's getting in jazz hands.

No, no it's not exactly Manhattan transfer level.

Uh, he's intermediate. Yeah. Uh, yeah. So again, bridges to the. Yeah.

You know, I bet we're going to hear from some folks because there are bridge enthusiasts. Yeah. Which I think is kind of neat. Yeah.

Well I mean they're like modern marvels of engineering and actually there's some ancient marvels of engineering too as far as that dude they are.

Yeah, they're basically I was talking to our pal Adam, the architect of the bridge builder.

No. Yeah. He's a building builder or a building designer. Yeah. I don't know if he actually knows how to build the buildings. He just knows how to tell the people how to build that.

Adam can't swing a hammer. So he was saying that the, um, basically the structural engineers who design bridges are just straight up geniuses. Oh I'm sure like it requires a basically genius to to factor in all of this stuff. Yeah.

Anyone can design a building, you know, with just four walls and a bunch of floors. Right. Put a roof on it.

Bridge, though. It's different. Yes, right.

There aren't walls really. Um, there can be bridges of Madison County. They had walls. Oh yeah. They have walls. I was going to mention the bridges of Madison County.

Yeah. I love those. That'd be a beam bridge I guess. Near with a truss. Right. Top truss.

What's the top truss called.

Through Truss. Yeah, through Truss. And then below that, if it were below it'd be a deck truss.

But I don't know if that counts as a trust. It's more just like a house on top of the bridge.

I bet there's structural support there. Yes, maybe it was mainly just to keep the rain off of you when you cross the bridge like just an extra little. Thank you for crossing the bridge.

I thought it was just to draw in lacky tourists who wanted to have their picture made another famous bridge, the one that the Headless Horseman couldn't cross, and the legend of Sleepy Hollow.

Oh, yeah. Wouldn't that a bridge? Sure. Trolls live under bridges that draw bridges are pretty cool. If you ever see maximum overdrive at the beginning of that movie.

Um, it's been many, many years. I saw it again eighties.

I saw it again very recently, like this year. And it really it's maybe better than it was before. It holds up as a crappy movie still. Yes. Yeah.

The whole soundtrack is AC DC, by the way, which you should love. Uh, whole soundtrack. I do love that. And I do remember that. And didn't Stephen King direct that. Yep. Which he doesn't do much right.

No, there may be is only one was definitely his first. Interesting.

But there's a great draw drawbridge scene in there. Uh did someone jump it. Jump the span. As it raised no, I think their car fell into their truck, fell him OK, because usually the drawbridge scene is like I can make it.

Uh, no, this one was you're all doomed. Yeah. You're making a scene. Gotcha. And let me also recommend Budapest for Bridges. You mean I went through the past a couple of years ago?

Yeah. I went there like 20 years ago. OK, so, yeah. You know, the bridges are amazing.

I think like five. Yeah. Because they connect the two sides.

Yeah. Buda and Pest. Right. And each one is totally different, like just a completely different design. Yeah. And they're just all gorgeous. Yeah.

Let's just start with a bunch of bridge recommendations. I'm going to recommend the city of Pittsburgh. Oh yeah. Uh, I went to a baseball game there and it's just gorgeous. There's beautiful bridges that you can see from the baseball stadium and the river.

That was when we were shooting a Toyota commercial, right?

Yeah. I stayed in the hotel and just ate saag paneer. No chicken SOGGE. Right, just like a quart of it.

But you could see the baseball stadium out your hotel window.

Yeah. And I saw some bridges, too. Yeah. You walk across the bridge to get there, right? At least we did. What else, any other bridges? Well, Brooklyn Bridge, Shuren, Golden Gate Bridge. Yeah, this is like the famous ones are barely even worth mentioning.

Yeah, but the Brooklyn Bridge is for your money. It's which is free. It's a pretty great thing to do to walk across it. It's it's just beautiful.

I have never done that. Yeah. You should do it. Even the Geico lizard did it and I have it. That guy's like Australian or something.

Well maybe we should just animate you and have you walk across it.

One more thing. If you want to know more about the Brooklyn Bridge, I don't remember which one we talked about it in, but there is a really cool documentary about the Brooklyn Bridge and it's building. Yeah, by Ken Burns. Oh, wow. I believe it's on Netflix.

I have to check that out then. Yep. Because I like Ken Burns and Brooklyn Bridges. Yeah. All right.

You ready? Uh, yeah, man. So Bridges have been around for a very long time. This article is by Robert Laham and another dude named Michael Morrisey. Together, I believe they were locked away in a closet for like a couple of months while they worked this out together.

Well, the one of the first ones talking about ancient bridges that they mentioned in here, the Arcade Deco Bridge in ancient Greece, did you see that thing?

No, it's really neat. I mean, it still stands. It's a 3000 year old bridge. And it's just kind of cool to think about, you know, ancient civilizations in ancient times. People said, well, I want to get over there. Right. And I'm here. Yeah. And so let's build something to do that. I need something to walk on. Yeah. Or drive my car over. It's that simple. I saw that I saw the world's oldest bridge that's still in use is in Turkey over the.

Muralists River, I believe. Yeah, from 850 B.C.. Do you know what that means, how it's constructed? It is just struggle. It is a single stone slab. Arch. OK, no, it is a stone slab, single arch. Yeah, that makes sense. Yeah, very basic.

Yeah, but the arch. It's super old, but it's still in use today.

Oh, yeah, because whoever figured it out came upon this very elegant solution to a lot of problems that a bridge poses, because as you were saying, when when you come upon like a river or a creek or something, you say, I'm on this side and I need to be on the other side. So I need something to walk across. Yeah, OK.

It's a basic solution, but the further and further you get, the more and more problems like, as bridge builders say, most spane mo problems.

Yeah, I guess what we should have said is I want to walk across and live. I want to walk all the way across.

Right. I don't want to fall down. No, I don't. To get halfway across and have it snap. Right.

So over the years as people have come upon problems where you are going to build a bridge that will snapping and kill you, they've come up with solutions to prevent that from happening. That's pretty much the pursuit of bridge building. Yeah. Is coming up with ways to prevent a bridge from collapsing. Yeah.

And a lot of trial and error over the years, you know, and a lot of real significant disasters. In fact, there's a TIME magazine slide show called Worst Bridge Collapses in past 100 years.

And it's got all these photos of collapsed bridges and little descriptions and the number of fatalities and everything. But it's really interesting. All these different bridges have collapsed and failed for all these different reasons.

Well, and after each one, uh, it's very sad, of course. But after each one, someone goes, oh, well, we should do this for the next one. Right.

We should not forget that Boult next time. Well, that could be human error, too. That's happened. Yeah, I'm sure.

Oh, all right. So should we start off with the bats?

The bats, beams, arches, trusses and suspensions are the main components, the structural components of a bridge.

It's very simple. Boom. That's it.

That's all you need to do to construct your own bridge. And with these four things, you can make almost any kind of bridge. We're going to cover mainly beam bridges, arch bridges, truss bridges, suspension bridges, and then the super cool looking cables, state bridge.

It is super cool and probably my favorite looking bridge in the world that I came across in researching. This is a cable state bridge, the one that's in the article. Oh yeah.

They look like click sails. It's gorgeous. The big triangles rising up. It's lovely. Yep.

But they look a little more modern to me. They don't have that classic architecture like the Brooklyn Bridge does or like the Tower Bridge in London.

Yeah, I think that's why I like it. Yeah. You like the modern look. Yeah. Yeah. You're a modern guy.

I'm a supermodel. All right. Um, they point out in the article, which is very key, what you talked about, the span of the bridge is the distance between the supports and that's where that's where it all goes down basically.

Yes. That's got to be strong there.

Those are something that every single bridge has is a span and at least one supports most likely to.

Yeah, yeah, yeah.

And there's different the reason that there are different types of bridges is because different bridge designs that that Bat's designs, what is it. Beams, arches, trusses and suspension. They provide stability for varying span lengths. Yeah. So like a beam, if you have like a 50 foot span, just put a like a very long log over over the span.

And there you go, there's your bridge. But as you get further and further along, you have more and more problems supporting that span. So you need different types of solutions and the different length of the span calls usually for a specific type of bridge design.

Yeah. And generally it'll mean there's a lot of overlap, of course, but being bridges tend to be the shortest, followed by arch bridges and then suspension bridges. Right. And I think those the cable state bridges is kind of a suspension bridge. So that counts.

It's like a kind of a variation. Yeah, but they can be very long as well. Yeah.

Yeah, not quite as long as suspension bridges though, from what I understand. And yes, the suspension bridge of four is the longest span. OK, so you got a big long span. It's suspension time.

Yeah. And they're also super expensive. Yeah.

Suspension bridges because all the bridge builders know that you got a long span that you're trying to cross. You probably get some deep pockets and they're going to milk you for it. Oh yeah.

Every penny. Yeah. Yeah. Like you need a suspension bridge. I'm your guy. Yeah. Um, all right. So let's talk about there are a lot of different forces that can act on a bridge to make it not as stable. We'll cover a few of the other ones later. But the main two here early on, our attention and compression. Yeah. And. A very easy way to think about these two things as tension is like if you if you and I are pulling a rope here on one end and I'm on the other, we're going to pull that sucker tight and I'm going to fall over.

Due to your massive strength, I'm pretty huge, but there will be some tension in that rope.

Yeah, maybe between us is after you fall down. Yeah. And I start laughing. There would be tension, sure. But tension is the lengthening of something. Yes. Compression is the shortening of something. Yeah. Like a spring collapse. Right.

So it's easy to visualize when you're talking like springs and ropes and that kind of thing.

But if you're talking about just a single deck of a bridge, which you think of as one piece, it's tough.

It starts to get tough to visualize it until you realize that you have to look at like a bridge deck, like the roadway on the bridge.

Yeah. As really having a top and a bottom.

Yes. And force. Well, the compression acts in the downward motion on the top and the tension acts from underneath.

Coming up on the bottom right. So the bottom of the bridge underneath it of the deck is is going to be spread out under the force of tension. We're on top where it's being pushed down, compressed. That's compression.

Yeah. And they kind of, in a weird way, work together, even though they're sort of opposite things. They're definitely related. Yeah, right. And what will happen is if these if you aren't a very good bridge builder, um, buckling will occur when it's compressed on the top. Yeah. And snapping can occur on the bottom when tension is at work. That's right. All sounds very confusing, but if you just going to do is like put your hand out and look at it.

Right.

You know, and so or if you take and push down on your hand or on your hand. Right. And I'm saying sure. Like that. Yeah, like that.

The whole thing becomes very, very evident when you look at a beam bridge. Right. The most basic form of a bridge, like if you dropped a log over a river.

Right.

In this this thing, this article is the example of like taking a pair of milk crates and putting like a two by four across them.

Right. Let's do that.

If you put, like, a bowling ball on a bowling ball, Stan, so it doesn't roll around. Yeah, that'll be all on top of the on top right in the middle of your two by four, which makes up your Bembridge deck.

Right. You're going to see that it bows. And what you're seeing is that on the top it's being compressed on the bottom. It's being tensed, right? Yeah. And what you just done is add a load to that bridge. And there's two kinds of loads to start out with. There's a dead load, which is the weight of the bridge and all of its materials combined. Yeah. And then there's a live load, which is say, like the cars and the people and the trains and everything, that they add the extra weight while they're moving across it and everything.

And as you add this extra load, first of all, the bridge is already dealing with its debt load. Yes. Got to hold that up. That's job number one for a bridge.

Yeah. Like if you had a 300 foot two by four and two milk crates, it's going to sag in the middle just naturally. Right.

And it might even break. And there have been bridges that have been built that where the guy forgot to carry the one or whatever and they couldn't stand up under their own weight. And they collapse from their own weight. They collapse from the dead load. So job number one of the bridge is to support its own weight job. No.

One point one is to support all of the live load, the traffic that goes across it as well.

That's right. And the two ways that you're going to do this to counteract tension and compression are dissipation and transference force. Yeah, or transferring the force with dissipation. You spread out that force equally spread out over a wide area. And with transferring, you move the area of weakness to an area of strength. Right.

It's pretty simple. Yeah. They're kind of tough to distinguish sometimes. Yeah. You know what I mean. But for example, like the best example of dissipation is the arch, which will talk about how that works in the second. Yeah, but suspension bridges are best at transferring the the tension and compression forces. That's right.

So if you're if you're talking about a beam bridge, that most basic kind. The other thing they're going to do to make it stronger, of course, is used back in the old days, guys would then later iron and then steel would be some concrete mix then. Yeah, but the size of the beam is going to be really important. Like the height of the beam is important because the the top is going to experience stress, the bottom is going to experience stress in the middle.

Not as much. So a good eyebeam. Right. A good tall eyebeam is what you want. Yeah.

And I didn't realize that. That's why I beams are made like IBM.

It really is the center of like the deck or the beam or whatever. Any kind of beam is going to experience the least amount of compression or tension. It's really the top or the bottom. Yeah. So you don't have to put quite as much material into the center of the beam as you do the top and the bottom to prevent buckling and snapping.

That's right. So the Bainbridge, you're going to add what's called the truss to make it stronger.

We'll talk about trusses more, but it's basically a triangulated strength and you'll see a truss if you've ever seen like a train bridge, like you see a truss on top or like in areas where they get a lot of snow, roof supports will frequently be trusses.

Yeah. And that's a three truss on top, we already said.

And if it's underneath, then it is the deck truss. Right.

And you can have both, but usually like with the railroads, you'll see like that top truss, not the same as a trestle. That's different, right? That's like like a roller coaster, you know. So after this break, why don't we talk more about truss bridges? Nice.

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So, Chuck, no joke. Trusses are one of my favorite things now. It's pretty neat.

After doing some research into them, I'm like, I love trust your trust guy.

Yeah. And it's because they're so elegant and simple. They're elegantly simple basically. Yeah. So I saw this really great explanation where it was on Make magazine and I think it was called like ask make how do trusses work. Pretty straightforward. And it basically had like a really great graphic of taking using popsicle sticks. Right. OK, let's say you make a square out of Popsicle sticks and you join the popsicle sticks together at the corners where the ends all meet.

Yeah, a little Elmer's paste maybe makes sense. Seems pretty supportive. Right. But when you press down on any one of those joints, which is where the loads going to be centered or distributed most. Yeah.

Remember the ends of the square shifts to the side and all of a sudden you have a rhombus.

Well, rhombus is inherently less structurally sound than a square, which is why you very rarely see rhombus in architecture.

Right, right. With a triangle. When you press down at any one of the joints, it distributes that compression or tension directly through the center of the beam. Yeah. So the triangle stays totally rigid. And when you add the more triangles you add, the more support you have.

So they're like basically like as far as a shape goes, the superconductor of transferring or distributing compression or tension.

Yeah, that's a good way to put it. And that's why when you see that that train trestle and that has that truss on top, it's got all those beautiful diagonal pieces of metal.

Right. And it's not just for for looks, even though it is cool looking. No.

One of the other great things about a truss is that there, you know, it's like just a three steel beams or three whatever aluminum beams.

They're just three pieces of metal usually fixed together. And that's that's the other key that I left out.

They they have to be connected at the ends. Yeah. Equally distributed from each end. Right. So let's say you drill a hole, the rivet one side of the truss to another one into the truss to another in the the other end has to be equally far away. Right. Do you see what I'm saying.

Yeah. Yeah. OK, they wouldn't just be like just drill that other one way over.

So anyway you have to the the place where the truss sides join together has to be on the ends. Yeah. And then but one of the things that it allows for is for wind blow through it easily. Oh sure. That's a huge point about trusses. Yeah.

They're not solid in that. They don't, they don't put up a lot of resistance to when they allow it to flow through, which is really kind of what you want. We'll see when you're building bridges.

Yeah, I think even the covered bridges have is more of a lattice type thing on the sides, right. Yes. It's not solid is it. That bit dumb. A covered bridge. Yeah. Yeah, they're solid.

I thought the walls were usually like a lattice so when could pass, you know, and they had that roof and like al-Atassi side. Is that right. Yeah. Maybe there's all kinds.

Yeah. I think those are just to keep the rain off. Oh, yeah, that's what you said earlier and keep shooting down the serious structural thing.

Yeah, but anyway, trust is rock, I guess, is what I'm trying to say.

Yes. There's your T-shirt. Trust is rock. So are we at Arches? Do we say that they frequently use trusses to support beam bridges? Yeah, OK, arches.

Now when we say a bridge is an arch bridge, the deck is not some big hill that you drive over. The deck is flat arches underneath. Right. Yeah, yeah, and you can have a single arch if you're Spanish that long or you can have a big one with like six or eight arches, although I've seen I think there are like.

Sure. Arch bridges that actually do go up and down. Oh, sure.

You know, like I mean, there's a natural arch bridges. Like rock formations. Yeah. Like that. And that's why they're still standing.

There's, there's, there's a bridge that forms like a perfect circle.

So like when when you see it reflected in the water, it just looks like a circle.

Oh Nido that's. Yeah. Arch bridges are pretty cool too. There are no trusses but they're beautiful in their own way.

Yeah, that's true. Uh, so the arch is obviously semicircular.

Um, and like you said, if it meets the water and reflects nicely, fully circular, circular, uh, and the entire form is going to divert weight onto what are called abutments. And this is what takes on the pressure. It's like, uh, I mean, if it's just a single arch, those abutments are probably going to be part of the earth right on one side or the other.

Yeah.

And the whole point of an abutment is when you press down in an arch or when gravity pushes down on it or it's compressed, that force goes downward and it makes the sides of the arch go out. Yeah, those abutments press inward so that the force of compression just goes straight down through the arch circle, the semicircle and into the earth or into the ground or whatever.

Yeah. And it's the arch. The what I thought was interesting, it's really all about fighting that compression. There isn't a lot of tension. Right. That comes into play with an arch bridge.

I think the tension is grows more and more possible when the degree of the ARC or arch grows.

Okay. Yeah. So that could come into play. It can.

But for the most part, when you're building an arch, you have to worry about compression more than tension. Gotcha.

Yeah. So there's stylistically and artistically design wise, there are all kinds of arches, baroque arches, renaissance arches, Roman arches. They were the Romans built, you know, arch bridges that are still standing today. Yeah. Have you been to Rome?

Yeah, man. It's just like you're walking along and all of a sudden you look to your left and there's like a 12 year old aqueduct. Yeah. You know, 1500 year old arch just sitting there. Yeah.

I remember the first time I went to Europe coming back and being sort of like, bummed out, you know, because we're walking along. And then there's the Burger King, you know. Yeah, this house is 200 years old. I should go to Rome.

I know my house is like 80 years old and it seems super old. Yeah.

Nothing up by Roman standards. No. But, you know, a little drafty in those thousand year old apartments.

Yeah, but it's so neat, though, because, I mean, like there's so much old surviving stuff. Yeah. That not all of it's even meant to be preserved.

Some of it's just like just there, it's not like a part of a park or an historic exhibit. It's just part of the city.

Yeah. You know, yeah.

I've heard other tourists complaining about how dirty Rome is and I'm always just like, come on, it's like focusing on the wrong path.

It's been around for a long time. Yeah. Um, oh yeah. That too. Yeah. And also, yeah. Don't be stupid and just look around you like they're complaining in front of a twelve year old fountain.

I didn't notice that it was particularly dirty. I mean it wasn't any more dirty than like New York or. Yeah.

Any other big city. I agree. But the, the thing with the arch though very stable once you get it built. But the building process. Oh yeah. It's tricky because until you connect those two ends, that's what gives it its strength. So until that happens, it's a little dicey.

Yeah. Yeah, yeah. Have some scaffolding.

Yeah. And they used to build wood scalf scaffolds and supports. Yeah. To hold the thing and then you just would build it in and now they use suspension cables like uh I think the biggest arch bridge on the planet is West Virginia's new River Gorge Bridge. And that thing is unbelievable.

It really is. And what's cool is when you look at it, um, it just it uses the cliff walls, the walls of the gorge as the abutments.

Beautiful stuff superstrong.

And that's where we're going to talk about that and our base jumping.

I know that's the fact that ties these two podcasts. Yeah.

That's where they have bridge day talk about elegantly simple.

So suspension bridges for my money are where it's at. I think they deserve their own, um, episode. Oh yeah. I'm pretty much that complex. Like this is just the briefest overview of Bridges in general, but especially with suspension bridges. It feels like there's just so much going on with those things.

Yeah, I agree. Ken Burns did like an eight hour long documentary on the Brooklyn Bridge alone, and it's true, he's a deep diver, really is. Were over of you guys. Yeah. With a giant helmet to go over his giant haircut.

That's a pretty big hairdo. Um, all right. So suspension bridge, as we mentioned, of course, Golden Gate Bridge and the Brooklyn Bridge. This is when you have your deck. Your roadway is suspended by cables. Yeah. Between can be a number of them, but, uh, to at least two tall towers. Right. That are supporting all of this weight and compression is pushing down, traveling up to those cables and transferring all that compression through all those lovely cables.

Right. So, I mean, another way to look at it is exactly what it sounds like. It's the bridge is suspended from cables, right? Yeah. But if you really start looking into what it's doing, it's not just holding these things up. What's what's going on is there's a transfer of that natural compression of the deck. Yeah. Up through the lines. Up through the cables up there, up to the towers, which, like you said, send them down to the earth.

Right. So the the towers that hold the bridge up are at the same time distributing or dissipating the forces of compression that are trying to pull the bridge down into the water below it. Yes. And the tension you also have to deal with as well. And apparently you deal with that using another part of the structure of suspension bridges, which are called anchorages.

Yeah. Now, that's just what the towers connected to at the base right now. No. So it's like other anchorages is like the abutment essentially.

Yes. Yeah, yeah. They're like left and right there like a suspension bridge is abutments. Whereas as you get closer to the middle of the bridge, that's where the towers are. Yeah. Yeah. But on the very ends, like, say, where the roadway hits the bridge, you're going to have a massive piece of rock or massive piece of concrete. And those are the anchorages. And you have horizontal cables that distribute the compression from the bottom of the bridge to the anchorages in those those transfer those into the earth.

Yeah.

And you might also, depending on the size of your suspension bridge, have to have that below deck truss as well to help stiffen the deck. And, you know, if you have a 4000 foot bridge, you're going to have all kinds of trusses and decks and cables. And I think I finally figured out what it is about bridges that I love. Is that the. The Arquit, the structural design that it needs to be strong, also happens to be beautiful.

Yeah, you know what I mean? Like the way the cables are arranged, it's not like they're like, oh, this looks great. It's like, well, it has to be like this. Right.

But it also happens to be very striking, like Grace Jones, you know what I mean? Yeah, absolutely.

So so suspension bridges are your favorite, huh?

I like it because there's so much going on. Yeah. Like trusses because they're so elegantly simple and they're just tough as nails. There's a bridge for everyone.

I think it really is the cable state bridge. And we should say that suspension bridges. When you think of a suspension bridge, you probably probably think of the Golden Gate Bridge or something like that, right? Yeah. Just a classic suspension bridge to towers to anchorages suspension cables, the suspension bridge. And you think, well, they're probably pretty new. Wrong suspension. Bridges have been found in various forms for hundreds of years at least. And apparently the enka were masters at building rope suspension bridge is out of woven grass.

Crazy man.

Yeah. 1400's they've discovered the Spanish conquistadors stumbled upon. These were like, what in the world is going on here? Right. Because the smart Europeans didn't figure this out for another like few hundred years after that. That's right.

The the Incas still have one of these bridges intact. It spans 90 feet and they remake it every year as part of a three day festival.

Oh, really nice. Yeah. Which is why it's still intact, because the grass woven grass Rockbridge didn't last all that long necessarily, even though when it's fresh and new, it's strong.

Yeah. As an expiration date. Right. You're saying. But apparently as we'll learn, all bridges have an expiration date. All right. Well we'll take a break then with that tease and talk about the cable state bridge and then how you might die on a bridge one day.

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All right, so we're on to your favorite, my friend, the super sleek, modern looking cable state bridge, which is actually actually actually has been around since, like World War Two.

Yeah, but the idea which is so modern, the idea came from a dude named Foust Rancic. Yeah, man. And he was a contemporary of Kepler and Brahe. And he basically came up with the first design for a cable stage bridge back in the 16th century.

So what's the nuts and bolts of this thing? So basically it is a rather than two towers like a suspension bridge, uses a cable state bridge, uses one tower. Well, not always.

There's plenty of them that have more than one, but OK. But for a particular span of bridge. Yeah, there's one tower supporting that one span. Right.

So it's basically you can't use it for as long of a span as a suspension bridge. Right. But if you have a slightly shorter span and you don't want to spend quite as much money and you don't want as many wires up there and everything, you can go with the cable state bridge. So you have one usually one tower holding up all the cables and the cables can either all connect to one point, which is called a radial pattern. Yeah, right.

So it's like all these different cables are connecting on the bridge deck at different points. Yeah, but they're all connecting at about a single point on the tower.

Again, architecturally lovely. Very neat looking. Yeah. And then another way that you can do it is in a parallel pattern. So they're connected at different points on the deck and they connected different points on the tower. And that's the case with the Erasmus Bridge, which I think is the most beautiful bridge in the world in Holland.

Oh, wow. Well, that didn't surprise me.

I mean, look at that thing. Look at that. POW! Oh, yeah, it's something else. Yeah, I wish you guys could see this. Well, they can look it up.

It doesn't look like very much though.

No, it looks very, um. It's like the New Holland, I guess. Yeah, New Amsterdam.

I'm just picturing like Holland, I think of, you know, wooden windmills. Oh.

And like tulips and stuff like that. Yeah, sure. Yeah. This is modern Holland. It looks like something that would be like Sydney, Australia.

Well they have great bridge too. They do. Mm hmm. Maybe that's what I'm thinking. Um, living. Well, you done with those?

Well, I was going to say another design for cable state bridge looks a lot like a sailboat. Yeah. With the the tower standing straight up and then on each side, cables going down at a diagonal from it to make it look like a sailboat sail. Right.

And mast and again for structural integrity more than anything. Right. Um, living bridges. Mm hmm. Sure.

Uh, well, I guess we should say cable state bridges are, uh, they can't be as long as suspension bridges, but they can be pretty long. Yeah. Like up to close to 3000 feet.

But that's what I'm saying. Like if you have a shorter span and you don't want to use as many materials and hence spend as much money, cable state bridge is a great alternative.

Yeah. I wonder when cities I wonder what the considerations are. Like money, what you, I would guess, money, first and foremost, money, what you probably is best for the the land. But I also bet that architecture comes into play like how it looks in the cityscape, don't you think. Yeah.

Like usually a city will have some sort of will accept several designs, competing designs and then probably well like in Atlanta's case with the 17th Street Bridge goes with the cheapest one and then half of it falls down on the traffic later like a couple of years later.

Did that happen? Yeah, I win like two two years ago. Really? Yeah. I mean, it was a big deal.

Luckily, it happened at like 4:00 in the morning or 5:00 in the morning. But like, when you're walking on the bridge, you know the side stuff.

Yeah, one whole side fell over on the seventy five below under the under the connector right below.

Yeah. I kind of remember that. Yeah.

But it's an ugly bridge to begin with really. And dude if you're listening, the guy who designed it.

I'm sorry, I don't mean to insult your work but I, I do better it just the city could have done better I think. Yeah. But I think what it came down to I'm sure was all of these are beautiful but we're just going to spend the money on this one.

Right. You know, or whoever got the biggest kickback. Yeah. Or whatever that came from. Right. Not to be cynical living bridges.

Yeah. We were talking about that. Um, if you go to northern India to the here we go. The Meghalaya region, I think that was good. All right. Close enough. Um, they have something pretty remarkable and they are called living bridges. And what they did was it's so rainy there that all of their natural bridges were having a hard time staying intact because of all the moisture. Yeah. From monsoon season. Yeah. And that's you know, you can't have a natural bridge with that much water.

So they said, why don't we take these tree roots and grow them out of the ground and span a river over the course of years and years and years and then basically planet on the other side into the ground. And this is now a natural tree road bridge.

Right. It's like giant living bonzai. Like they were training to go a certain way and they would take a, um, a tree, a felled tree and split in half and use that as the guide. Yeah, right. It's like the structure. So sure they were building an arch but they weren't making an arch like sort of a temporary bridge.

Exactly. And they let the roots grow along that and like they would plan these things out or they do plan these things out over the course of like a decade. Yeah. And I get the impression it's the whole town's responsibility, at least some people in the town's responsibility to make sure that if you see your roots starting to go down in the wrong place, you just pluck it up and put it back on that fell log that's guiding it across the way.

Yeah, it's pretty neat. Like, it requires patience, obviously. But it also, um, I imagine just once a day someone walks down and is like, you're looking good. Yeah. And then just walks away again.

Pets' The bridge says keep growing or walk across in ten years, buddy.

And apparently those things can last up to 50 years or the largest one that they have up to 100 feet, which is 30 meters for our friends in India. Crazy.

And it can bear the weight of fifty people and lasts up to five hundred years, not fifty. That's what I said. Oh, I thought you said fifty as a fifty people. Oh well it's crazy. Like you got to Google these things. Yeah.

They're very pretty. Very pretty. It looks very dark. Cresta Lee. Oh yeah. Totally, you know what I mean. But they're not unsettling at all. No.

Like the dark Crystal Wright, which by the way, if you're ever in Atlanta, sometimes people say, hey, I'm coming to Atlanta. Yeah. What should I do? Go to the Center for Puppetry Arts. Agreed. And just look at their free exhibit, which includes a full sized sexy. It's terrifying.

Yeah, they have all we've talked about this before. They have imitator, you know, place. That's right. For me, that was pretty, pretty magnificent. Oh, it meant a lot for Emmett. Honor to meet you, too.

Um, they're doing actually, I saw I was just at the Museum of the Moving Image in Queens.

Oh, yeah. I saw you post something about that. Yeah.

They have a Mad Men exhibit right now, which is pretty neat, but it was pretty cool. They I was not there in time for the Jim Henson when they're putting that in place I think for late. It's coming. It's coming. Let's get you miss it.

Yeah. Well yeah. I'll just go back.

Oh we went to the Yoko Ono exhibit at MoMA. Uh huh. Awesome. She's something else dude. She's got a pretty cool mind. Yeah.

She had, she had this one display and it was titled Three Spoons and it was just four spoons in a row.

It was in three. You know, I love that stuff. Yeah. So I recommend that as well. I'm not a fan of her music, though.

I actually got turned on her music in the listening room there. Yes. They go a band. It's crazy. Weird stuff, but I kind of like it. I mean, she's definitely one of the the most like original thinkers, you know, out there and she's been at it for a while, like a lot of the stuff went back to the 60s, like the early 60s.

Yeah.

And talk about weathering criticism and still just being like, screw you. Yeah. I'm Yoko Ono. I don't care what you say.

Well, she was exonerated, too, recently. Remember, Paul McCartney came out. Yeah. So like it was not Yoko Ono that broke up the Beatles. Stop saying that. It just took them like 50 years to come out and say it. Yeah.

You know, she's like, would it kill you? Right. You've told me privately many times, but. Well, press releases tweet. All right.

So we talked about compression and tension being the two main forces. Uh, there are quite a few other forces, dozens even that can act on a bridge in a negative way. And the scariest one for my money is TORSHIN. If you've ever seen the video, it's very famous video of the bridge. What is it?

The Tacoma, the Tacoma Narrows Bridge. Tacoma Narrows Bridge when it looks like a wet noodle twisting in the wind.

Yeah, it was 1940. It's nuts. And they have like footage of this whole thing just undergoing this destruction that kept just going on and on and on. And finally, the bridge just comes down.

Yeah. The craziest part is when you're watching it, you just think, oh, man, look at that thing. It's nuts. And thank God there's no one on it.

And then you see, like, a dude walking on it and a car. Yeah.

And a guy ran. There was a dog. There's one car in there and there was a dog trapped in the car. So some guy ran and got the dog. Oh, he did. Yes. Pretty great heroic stuff. Sure. Then later on, I don't know if it's the same guy and another guy or just two completely new guys. They're just walking along it.

This is after a whole section has fallen into the river. But the section they're walking on is still swaying.

But it's like this the from the bridge step back from the bridge man. So that's Torshin at work. Yeah.

And that's a big problem that designers of suspension bridges face because you have a deck that's being held from it's being held aloft by cables.

Right. It's not like fixed to anything below it necessarily.

Yeah. I mean, they're being suspended. So just like on like a rope bridge or something like that, it sways very easily. Right?

Yeah, those towers are strong, but it's not, you know, directly connected to those towers. Right.

So if you have a swing bridge in between them. Right. And the thing is swaying back and forth. But if one side starts to sway over the other side and all of a sudden you have an opposing circular force and that's torsion and that can basically rip the bridge in in two, which is shear.

Yeah, well, that's the other awful thing that can happen. It can just snap. Well, not snap I guess, but just break in to two parts.

Yeah, well I mean snapping is the result of compression. Yes. Shearing would be what it's called technically. Yeah. Exactly where to the the same span of bridge has the two opposing forces acting on it at once in opposite directions. And it goes, it makes a terrible sound.

If you want to combat torsion many ways to do this, you're probably going to have a deck truss going on. Yeah. To help out. Truss saves the day that truss saves the day you're going to have you're going to do a wind tunnel tests if it's a modern bridge beforehand. Well, you're going to make a model. Yeah. And do test and see like how does wind affect this bridge and what do we need to do.

But the thing is, with the with the Tacoma Narrows Bridge in particular, they did tests. They had that thing rated withstanding winds of up to one hundred and twenty miles an hour. But the winds that day that brought it down were only 40 miles an hour. And for a long time they were like, what happened? And somebody said, you know what it was? It was mechanical resonance.

It was, yeah. The deck truss was not sufficient for the span that was part of it and the way the wind hit it. Right. And the angle caused the final thing that he just mentioned, resonance, which is sort of it's a vibration basically that gets out of hand.

So resonance to me, I think deserves its own podcast, too. It's awesome.

Everything, every especially anything that we build from an airplane to a bridge to watch it.

It has a certain frequency where it will really pick up force, really absorb force.

It'll run through it. Right. So let's say that your bridge has a resonance. That's like at a frequency of ten. Yeah, that's probably a totally ridiculous number that I just said.

But let's say it's ten, right. And then let's say that wind comes at it at forty miles an hour at just the right angle and it makes its way at a freaking. A sea of nine, well, that is going to be it's just going to sit there and sway, not a big problem if that wind hits it at just the right angle, at just the right speed and it starts swinging at 11.

It's still not quite a problem. Yeah, but if it gets it just right and it starts swaying at 10:00, all of a sudden those waves are going to become more and more pronounced because all that energy is flowing through at its maximum potential, at its freest flow, because it's hitting the bridge at its natural resonance, right?

Yeah, and that's what caused the Tacoma Narrows Bridge to come down, because once that thing starts going, there's no coming back from it.

Oh, yeah, we because see it happening, it gets worse and worse. Exactly. And that's that's because it hit it at just the right frequency. Yeah.

They liken it in the article, which I think is pretty down to earth of a snowball rolling downhill. Exactly.

It just keeps getting worse and worse and you can't stop it. So but isn't that bizarre that a bridge has a natural resonance, a natural frequency?

I don't think so.

Like, I would assume it would vibrate. Yeah, it did not occur to me at all.

And I was talking to Adam about this, too, and I was like, so I saw that building designers, bridge designers, they will fine tune like a structure so that it resonates at a frequency that it's probably never going to encounter from an earthquake or from winds or whatever.

Yeah, I'm like, how do you do that? And apparently it comes down to the building materials you use, the shapes you use to form the structure, the way you join those shapes together. And you can basically say, I'm giving this building a frequency of one point five. Right. Whereas I know all the wind in the area and the ground movement from an earthquake is going to make it vibrate at a frequency of seven. So it'll be fine.

Yeah. And one way, like you said, they can do that is by not having like one like shortening the sections of the déclassé. Yeah. And that way the vibration, when you have these overlapping plates and smaller sections, it's going to create enough friction to disrupt that frequency. Right.

It'll change the frequency that the moving it. But I mean and not just bridges, too. You have to take this and take into account like airplanes. Right. Or you can't use engines on airplanes that create vibrations at a frequency that's at the natural resonance of the airplane body. That's the airplane body is going to come apart just from turning the engines on. Yeah.

Could you imagine seeing the airplane wings starting to flap, like, harder and harder? Right.

But apparently the the more common thing when you have a disaster, a catastrophe from a resonance, a mechanical resonance problem, it's like one bolt is like I can't take it anymore and stops.

And then that leads to a cascade of failures that ultimately has the bridge coming down.

Yeah, interesting. I think that's fascinating. I had no idea that you had to worry about frequencies and vibrations.

I mean, why all the bridges you've built have collapsed, collapsed pretty easy. Well, if you've ever heard the old they go down like a French boxer.

That means I don't need it was a Glasgow reference. Remember him from Mike Tyson's punch out? Oh, no. Is that why you guys counter? He says he was French glass Joe got a glass jaw and he went down just like a sack of potatoes. So easy, man. Well, which was it?

A sack of potatoes or a French boxer? He was both. He went down like a sack of French potatoes. Yes, French fries. Right. My bridges go down like a French boxer. But Glass Joe, the French boxer, went down like a sack of potatoes. Ergo, my bridges go down like a sack of potatoes.

Um, if you've ever heard the old wives tale that like an army marching across a bridge in step can cause enough vibration to take down that bridge. Yeah, it's true. That could happen. Yeah.

So if we're tied at the right frequency, right. Yeah. In wartime that's they will break step. In other words their rhythm isn't all the same to avoid that scenario.

And there was a bridge disaster I saw in that Time magazine slide show where that happened. There were there were a pair of skywalk bridges inside the Hyatt Regency Kansas City Hotel in the lobby. They were just like, you know, raised bridges. You're going through the lobby. And they collapsed in 1981 and killed like a bunch of people because a 30 something people, people marching, dancing. They were dancing on the skywalk.

And you think like, well, up to today or yesterday when I started researching this. Right. Like, I just thought that's weight or pressure, something like everybody's dancing. It never occurred to me that the rhythm had something to do.

Oh, really? See, I'd always heard that. Well, you're far more advanced than I am the structural engineering, my friend.

Not that it's just always heard that, like, you know, even a bunch of kittens walking across could cause that. And the reason they said kittens, of course, is so it has nothing to do with weight.

Right. Because kittens doing nothing. And consequently, I think Lionel Richie had to change the name of that song because of the accident. I think originally it was. Hello. Oh, what a feeling when you're dancing on the skywalk.

And he had to change it to ceiling and everyone was like, that's weird. Dance on the ceiling, but it rhymes.

And he's like, Yeah, but nobody ever died from dancing on the ceiling.

I guess the final thing we should mention is that weather, um, obviously will play a big impact. We already talked about wind, but over the years, the materials they use and the design is, uh, gone in to take account things like wind and, uh, what sun damage?

I don't know. I think the freeze thaw cycles huge. Yeah. Salt. Sure. Salt exposure. If it's going over like a salty body of water. Yeah, it makes sense. Yeah. There's a lot of things that are trying to bring a bridge down.

Nature abhors a bridge basically as much as a vacuum.

I've got one which got there's probably around six hundred and thirty thousand bridges in the US alone because there are six hundred and seventeen thousand nine hundred and thirty five in the 2002 census. And they add them, they were adding them at about a thousand a year, maybe nine hundred a year. Wow.

That's just the U.S. The world's longest bridge completed in 2010, the Danang Kunsan Bridge.

I think I've seen pictures of that. It serves as a railway bridge for the Beijing and Shanghai railway. It's 102 mile long bridge that's nutty over water.

I'm a big fan of cities with multiple water bridges.

Well, that's why I liked Pittsburgh, Pittsburgh, Portland, Budapest. Yeah, I'm a big fan. Atlanta does. We have bridges, but it's not like you have to go to the Chattahoochee River, the lakes.

Nobody goes to the Chattahoochee.

You know what? Sure.

Um, I got one more thing I want to shout out to PBS. Build it. Big website. Yeah. Which is like beyond nineties as far as websites go. But it was extremely helpful in understanding the forces that work on bridges, different types of bridges, different specific bridges. Yeah, great website.

And thanks to Adam, I guess you got some information from him. Yeah. Thanks, Adam. Was he indeed talking to you about it or was he on the other end going, oh my God, just shut up. I'm watching Tim and Eric.

He was he was in to talking about it. I figured he would be. Yeah. And I actually have to shout out to you, too, because I told you we were building bridge or. Well, we were talking about bridges. She sent me a bunch of stuff on Popsicle bridges.

Um, apparently there's a Indiegogo for the world's strongest or Canada's strongest Popsicle bridge.

Wow. Yeah. They're trying to build that. Yes. For and they have like six grand already had four out of popsicle sticks. Good for them.

So let's everybody get in, shout it out to all over the place in this one, huh. Yeah. That's nice stuff. Bam.

If you want to know more about bridges, you can type that word into the search bar at HowStuffWorks dot com. And since I said search bar, it's time for listener mail.

Uh, I'm going to call this. I get a couple of street gang responses we'll read over the next couple of shows.

Okay.

Here's one I had to write in about your street gangs episode as it was interesting, pertains to my job. Short version is that I work for a hospital based program and we see every gunshot wound victim in stab wound victim comes through, which is about four to five hundred a year and about ten percent of those are gang involved. You guys have mentioned how you found the number of gangs to be hard to believe, but I think you may be thinking the street gangs is one entity that has strict borders and lots of people.

In my experience, larger gangs will sometimes incorporate smaller gangs and sometimes larger gangs will split off into many, many smaller groups.

Uh, people go in and out of gangs and are sometimes affiliated with more than one.

Currently we have about at least seventy in our city alone, and a substantial amount of those have less than twenty members.

So like many gangs, not super gangs, not super gangs. According to this paper on street gangs in Boston, 18 percent of the gangs in the city have less than 10 members and 34 percent have 10 to 19 members.

So while the numbers you gave seem shockingly high, they also seem to be in step with the current climate. And that is from Aryana.

And what city did she say? You know, I don't see that.

I don't think she said I don't know if it was Boston or if she just referenced Boston.

Well, thanks a lot, Arianna. We appreciate that email. And yeah, keep them coming. We want to know more about gangs. I just had the impression the whole time that, like, one way or another, we were officially or unofficially misinformed.

We may be. And also let us know who's the coolest famous person you've ever met. Uh, you can tweet to us as far as K podcast. You can join us on Facebook, dot com slash stuff. You should know you can put it in an email to Stuff podcast at HowStuffWorks dot com. And as always, join us at our home on the Web stuff you should know Dotcom. Stuff you should know is a production of I Heart Radio for more podcasts, my heart radio is the radio app, Apple podcasts or wherever you listen to your favorite shows.

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