Bridges: Nature Abhors Them

Josh Clark, do you Yeah? Every time I should listen to the Sometimes that explains the glazed overlook in your eyes whenever we start um bridges. Yeah, is that your intro? Ye? I like them. Maybe we can add like a scat drummer on top of that. We have that kind of um when we're doing uh listener mail, there's a little bit of oh yeah, well that's not scat drumming. I would say that's more of a shuffle mhm scots like yeah like that. Yeah, you should get Hodgment to scat

for you sometime. He's got a lot of boot boot bidus going on when he's scatting any jazz hands. No, No, it's not exactly Manhattan Transfer level. He's intermediate. Yeah uh yeah so again, Princess. Yeah, you know, I bet we're gonna hear from some folks because there are bridge enthusiasts, 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 they are.

Um yeah, there you Basically I was talking to our pal um Adam the architect o, the bridge builder. No, yeah, uh, he's a building builder. We're a building designer. I don't know if he actually knows how to build the buildings. He just knows how to tell other people how to build that. Adam can't swing a hammer. He was saying that, um uh the um. Basically, the structural engineers who designed bridges are just straight up geniuses. Like it requires a

basically a genius to factor in all of this stuff. Yeah, anyone can design a building, you know, there's just four walls and a bunch of floors. 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 that'd be a beam bridge, I guess, yeah, with a trust, right, the top trust was the top trust film a through trust through trusts, and then below that. If they were below it would be a deck trust. But don't know if that counts as a trust. It's more just like a house on top of the bridge. I bet their

structural support there. May thought it was mainly just to keep the rain off of you when you crossed the bridge, like just an extra little thank you for crossing the bridge. I thought it was just to draw in Lackey tourists who wanted to have their picture made. Another famous bridge, the one that the Headless Horseman couldn't cross in the legend of Sleepy Hallow. Oh yeah, wouldn't that a bridge? Sure? Trolls of under bridges that draw bridges are pretty cool.

Have you ever seen Maximum Overdrive? The beginning of that movie? Um, it's been many, many years. I saw it again. I saw it again very recently, like this year, and it is it's maybe better than it was before. It holds up as a crappy movie. Still. Yeah, the whole soundtrack is a C D C by the way, which you should love the whole sound I do love that, and I do remember that. And didn't Stephen King direct that, which he doesn't do much, right, No, but maybe it's

the only one is definitely far interesting. But there's a great draw draw bridge scene in there. Uh did someone jump it jump the span as it raised? No? I think their car fell into their truck felling. Okay, because usually the drawbridge scene is like I can make it. Uh No, this one was you're all doomed and uh, let me also recommend Budapest for bridges. You mean I went to Budapest a couple of New years as ago. Yeah,

I went there like twenty years ago. Okay, so yeah, you know the bridges are amazing that I think like five because they connect the two sides, yeah, Buddha and Pest, right, and each one is totally different, like it's 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 baseball game there, and it's just just gorgeous. Those beautiful bridges that you

can see from the baseball stadium and the river. That was when we were a Toyota commercial ring. Right. Yeah, I stayed in the hotel and just eight um sog copenny r no chicken sog. Right, it's just like a quarter of it. But you can see the baseball stadium out your hotel window. Yeah. And I saw some bridges to Yeah, you walk across the bridge to get there. Really swe did what else any other bridges, well, Brooklyn Bridge, Golden Gate Bridge, this are like the famous ones. They're

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've never done that. You should do it. Even the Geico Lizard did it, and I haven't. That guy's like Australian or something. Well, maybe we should just

animate you and have you walk across it. Uh. One more thing if you want to know more about the Brooklyn Bridge, I don't remember which one we talked about it, and but there is a really cool documentary about the Brooklyn Bridge and it's building by Ken Burns. Oh wow, I believe it's on Netflix. I'll have to check that out then, yep, because I like cain Burns and Brooklyn bridges, all right, you ready? Uh yeah, man, So bridges have

been around for a very long time. This article is by Robert Lam and another dude named Michael Morrissey together. I believe they were locked away in a closet for like a couple of months while they worked this out together. Well, he the one of the first ones that talking about ancient bridges that they mentioned in here, the Arcadeco Bridge in ancient Greece. Did you see that thing? It's really neat. I mean it still stands. It's a three thousand year old bridge, and uh, it's just kind of cool to

think about, you know, ancient civilizations and ancient times. People said, well I want to get over there, and I'm here, and so let's build something to do that. I need something to walk on or drive my card over that. Si Um, I just saw that. I saw the world's oldest bridge that's still in use. Um is in Turkey over the Mulis River, I believe from eight Do you know what that's how it's constructed. It is a single It is a single stone slab. Archy. 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 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 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, okay, that's a basic solution.

But the further and further you get, the more and more problems. Like, as bridge builders say, most span more 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 want to get halfway across and have it snapped. 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 is coming up with ways to prevent a bridge from collapsing, 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 um called worst Bridge Collapses in Past one years, um, and it's got all these photos of collapse bridges and

little descriptions and the number of fatalities and everything. But um, it's it's really interesting all these different bridges of lapsed 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. We should not forget that bolt next time. Well, that's that could be human Ara, True,

that's happened. Yeah, I'm sure. All right. So should we start off with the bats be A t s. Beams, arches, trusses, and suspensions are the main components of the structural components of a bridge. It's very simple, that's it. That's all you need to know to construct your own bridge. And with these four things you can make almost any kind of bridge. Um. We're gonna cover mainly beam bridges, arch bridges, trust bridges, suspension bridges, and then the super cool looking

cable stayed bridge. It is super cool, probably my favorite looking bridge in the world that I came across and reach researching. This is a cable stayed bridge, the one that's in the article. Oh yeah, they look like look like sales gorgeous, the big triangles rising up. It's lovely. 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 super mod alright. 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 um, that's where

it all goes down. Basically, Yes, that's got to be strong, there be those are something that every single bridge has is a span and at least one support most likely to Yeah you know, um, and there's different The reason that there are different types of bridges because different bridge designs that that bats designs what is it, beams, arches, trusses,

and suspension. They provide stability for varying span lengths. So like a beam, if you have like a fifty ft um span, just put a 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 it'll I mean there's a lot of overlap, of course, but UM beam bridges tend to be the shortest, followed by arch bridges and then suspension bridges, and I think those UM the cable stayed bridge is is kind of a suspension bridge, so that counts. It's like a kind of a variation that can be very long as well. Yeah, not quite as long as suspension bridges though from what I understand, and this UM, the suspension bridge affords the longest span. Okay,

so you've got a big long span, it's it's suspension time. Yeah. And they're also super expensive. Yeah, suspension bridges because all the bridge builders know that you've got a log span that you're trying to cross, you probably got some deep pockets and they're gonna milk you for it. Oh yeah, every penny. Yeah. Yeah, Like you need a suspension bridge I'm your guy. 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. Um. Will cover a few of the other ones later, but the main two here early on our tension and compression. And the very easy way to think about these two things is tension is like if you if you and I are pulling a rope, like you're on one end and I'm on the other, We're gonna pull that sucker tight, and uh, I'm gonna fall over due to your massive strength. I'm pretty huge, but um, there will be some tension in that rope. Yeah, f do you fall down? Yeah?

And I'd start laughing if there would be tension. Sure. The tension is the lengthening of something. 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, Um, it's tough to 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 as really having a top and a bottom. Yes, and forces, Well, the compression acts in the downward motion on the top, and the

tension acts from the underneath coming up on the bottom. Right, So the bottom of the bridge, underneath it, of the deck 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, right. Uh. And what will happen is if these uh, if you aren't a very good bridge builder, um, buckling will occur when it's compressed on the top, and snapping can occur on the bottom when tension is at work. That's right. It all sounds very confusing, but if you just I gotta do is like put your hand out and look at it, you know, and so or if you take and push down on your hand or on your hand, right, you know what I'm saying, like that, yeah,

like that. Um, 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, and this this thing. Um. This article used the example of like taking a pair of milk crates and putting like a two by four

across them. Right, if you put like a bowling ball on a bowling ball stand so it doesn't roll around, Yeah, that'd awkward on top of them, on top, right in the middle of your two by four, which makes up your beam bridge deck. Right, Um, you're gonna see that it bows, and what you're seeing is that on the top it's being compressed. On the bottom, it's being um tensed, right. Um. And what you've just done is add a load to that bridge. And there's two kinds of loads to start

out with. There's a deadload, which is the weight of the bridge and all of its materials combined. And then there's a live load, which is say, like the cars and the people and the trains and everything that that 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 deadload. You's got

to hold that up. That's job number one for a bridge. Yeah, Like if you had a three hundred foot two by four and two milk crates it's gonna 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 deadload. So job number one of the bridge is to support

its own weight. Job number one point one is to support all of the liveload the traffic that goes across it as well. That's right. Uh. And the two ways that you're going to do this to counteract tension and compression are dissipation and transference force or transferring the force. So with dissipation you spread out that force equally, you spread out over a wide area, and with transferring um you move the area of weakness to an area of strength, right,

which 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 we'll talk about how that works in a second. Um. But suspension bridges are best at transferring the um the tension and compression forces. That's right. So if you're if you're talking

about to beam bridge that most basic kind. Uh. The other thing they're gonna do to make it stronger, of course, is use back in the old days, use wood than later iron and then steel, maybe some concrete mixed in um. But the size of the beam is gonna be really important. Like the height of the beam is important because the the top is gonna experience stress, the bottom is gonna experience stress in the middle not as much. So a good I beam, a good tall ibam is what you want. Yeah,

and I didn't realize that. That's why I beams are made. Like I beam, the center of 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. 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 with the beam bridge, you're gonna add what's called a truss uh to make

it stronger. This uh, we'll talk about trust is more but it's basically reriangulated strength. And you'll see a trust if you've ever seen like a a train bridge like you see a trust 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 trust on top we already said. And if it's underneath then it is uh the deck trust and you can have both, but usually, like with the railroads, you'll see like that

top trust not the same as a trestle. That's different. That's like like a roller coaster, you know. So after this break, why don't we talk more about trust bridges? Nice? So, no joke. Trusses are one of my favorite things now, it's pretty neat. After doing some research into him, I'm like, I love trust. Yeah, and it's because they're so elegant

and simple. They're elegantly simple basically. So, um, I saw this really great explanation where it was on Make magazine and I think it was called like ask Make, how do trust? His work? Pretty straightforward, um, and it basically had like a really get a great graphic of taking using popsicle sticks. Right, Let's say you make a square out of popsicle sticks, and you joined the popsicle sticks together at the corners where the ends all meet. Ye,

little Elmer's paste. Maybe makes sense. It seems pretty supportive, right, But when you pressed down on any one of those joints, which is where the load's going to be centered or distributed most remember the ends the square shift to the side, and all of a sudden you have a rhombus. Well, rambus is inherently less structurally sound than square, which is

why you very rarely see rambus as in architecture. 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, 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 the 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 tress alone that has that trust on topics, got all those beautiful diagonal uh pieces of metal. And it's not just for for looks, even though it is cool looking. No. One of the other great things about a trust is that there you know, it's like just a three steel beams or three whatever aluminium beams. They're just three pieces of metal usually fixed together. And that's that's the other key that I left out. They have

to be connected at the ends equally distributed from each end. Right, So, let's say you you drill a hole to to rivet one side of the trust to another, or one end of the trust to another end, the the other end has to be equally far away. Do you see what I'm saying. Yeah, yeah, okay, they wouldn't just be like just drill that other one wherever. So anyway you have to the place where the trust sides join together has

to be on the ends. And then but one of the things that it allows for is for wind to blow through it easily. That's a huge point about trusses. 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 that's type thing on the sides. Right. Yes, it's not solid, is it.

That'd be dumb a covered bridge. Yeah. I thought the walls were usually like a lattice so wind could pass through. Now and they had a than a roof and like a lattice e side is there, right, Yeah, maybe there's all kinds. I think those are just to keep the rain off. Oh yeah, that's what you said earlier and keep shooting down there. Yeah. But anyway, trust is rock, I guess, is what I'm trying to say. Yes, there's your T shirt. Trusses rock. So are we at arches?

Do we say that they frequently used trusses to support beam bridges? Yeah? 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 the arches underneath, uh right yeah. And you can have a single arch if your span isn't along, or you can have a big one with like six or eight arches.

Although I've seen I think there are like short arch bridges that actually do go up and down, you know, like if there's natural arch bridges, like rock formations are like that and that's why they're still standing. There's um 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. Arch bridges are pretty cool too. There are no trusses, but they're beautiful in

their own way. That's true. Uh So the arches obviously semi circular. Um. And like you said, if it meets the water and reflects nicely, fully circular, fully circular. Uh And the entire form is gonna divert weight onto what are called abutments. And this is what takes on the pressure. It's like, I mean, if it's just a single arch, those abutments are probably going to be part of the

earth on one side or the other. Yeah. Um. And the whole point of an abutment is when you press down in an arch, or when you know, gravity pushes down on it or it's compressed, that force goes downward and it makes the sides of the arch go out. 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 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 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. So there's a stylistically and artistically design wise. They're all kinds of arches.

Baroque arches, Renaissance arches, Roman arches. They were the Romans built, you know, arch bridges that are still standing today. Um, have you been to Rome? Yeah? Man, it's just like you're walking along and all of a sudden you look to your leaps and there's like a two thousand year old aqueduct, you know, hundred 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 Burger king. You know, this is two hundred years old. She go to Rome. I know, my house is like eighty years old, and it seems super old. Nothing by Romans 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 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 part. It's been around for a long time. Um yeah. And also yeah, don't be stupid and just look around you like they're complaining in front of a two thousand year old fountain. I didn't notice that was particularly dirty. I mean, it wasn't any more dirty than like New York or anything any

other big city. But the thing with the arch though very stable once you get it built. But the building process it's tricky because until you connect those two ends, um, that's what gives it its strength. So until that happens, it's a little dicey. Yeah. Oh yeah, I had some scaffolding come on time. Yeah. And they used to build wood scalf scaffolds and supports to hold the thing and

then you just would build it in. Um. Now they use suspension cables like 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 or the walls of the gorge as the abutments. Beautiful stuff, super strong. And that's where we're going to talk about that in our base dumping. I know. That's the fact that ties these two podcasts together.

It'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, pretty, I'm pretty much they're they're 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. I mean, Kim Burns did like an eight hour long documentary the

Brooklyn Bridge alone. Yeah, that's true. He's a deep diver. We're over of you guys with a giant helmet to go over his giant haircut, because a pretty big hair doan UM. All right, So suspension bridges we mentioned, of course,

Golden Gate Bridge and the Brooklyn Bridge. This is when you have your deck, your roadway is suspended by cables between can be a number of them, but uh to at least two tall towers that are supporting all of this weight and compression is pushing down, traveling up through 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, 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 up through the lines, up through the cables up down up to the towers, which, like you said, send them down to

the earth. Right, So 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,

huh so it's like um anchorages is like the abutment essentially. Yes, they're they're like a suspension bridges abutments. Whereas as you get closer to the middle of the bridges, that's where the towers are. But on the very ends, like say where the roadway hits the bridge, you're gonna 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

um the anchorages and 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 um. And you know, if you have a four thousand foot bridge, you're gonna have all 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 arc, 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, but it also happens to be very striking, like Grace Jones, you know what I mean? Yeah, absolutely so. Um So, suspension bridges are your favorite, huh. I like them because they have so much going on. I like trust is because they're so elegantly simple and they're just tough as nails. There's a bridge for everyone.

I think there really is. Um the cable stayed bridge, and we should say that suspension bridges. When you think of a suspension bridge, probably probably think of the Golden gate bridge or something like that. Right, Just a classic suspension bridge, two towers to um anchorages, lots of suspension cables. It's the suspension bridge and you think, well, then they're

probably pretty new. Wrong. Suspension bridges have been found in various forms for hundreds of years at least, and apparently the Inca were um masters at building rope suspension bridges out of woven grass. Crazy man, Yeah, fifteen hundreds they discovered the Spanish concreteadores stumbled upon these were like, what in the world is going on here? Because the smart Europeans didn't figure this out for another like few hundred years after that. That's right. Um, the inc Is still

have one of these bridges intact. It it spans ninety ft um and they remake it every year as part of a three day festival. Really nice, which is why it's still intact because the grass woven grass rope bridge didn't last all that long necessarily even though why when it's fresh and new, it's strong as an expiration date what 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 stayed bridge and then um, how you might die on a bridge one day. Alright, so we're onto your favorite, my friend, the super sleek, modern looking cable stayed bridge, which is actually actually actually has been around since like World War two. Yeah, but the idea which is modern.

The idea came from a dude named um Fast Ranchica Man and he was a contemporary of Kepler and brahi Um and he basically came up with the first design for a cable stayed bridge back in the sixteenth century. So what's 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 um, there's plenty of them that have more than one, but okay, but for a particular span of bridge, there's one tower supporting that one span, right, UM. So it's basically you can't use it for as long of a span as a suspension bridge. 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 UM tower holding up all the cables, and the cables can either all connect to one point, which is called a UM radio pattern. Right, So it's like all these different cables are connecting on the bridge deck at different points, but they're all connecting at about a single point on the tower. Again architecturally lovely, very neat looking. And then another way that you can do it is UM in

a parallel pattern. So they're connected at different points on the deck and they connect at 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. Well that doesn't surprise me. I mean, look at that thing. Look at that pal Oh yeah, it's something else. Yeah, I wish you guys could see this. Look. It doesn't look like very Dutch 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 uh, you know, wooden windmills and like two lips and stuff like that. Ye. Sure, yeah, this is modern hauland for it looks like something that would be in like Sydney, Australia. Well, they have great bridge to they do. Maybe that's what I'm thinking, Um,

living bridge, Well, you are you done with those? Well I was gonna say another design for cable state bridge looks a lot like a sailboat, with 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 and masked and again for structural integrity more than anything, right, um living bridges 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 have to close to three thousand 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 hints, you spend as much money at cable State bridge is a great alternative. Yeah. I wonder when cities, Uh, I wonder what the considerations are, um, like money, what you I would guess money first and foremost money, what you probably is best for the land.

And but I also bet that that architecture comes into play, like how it looks in the city escape, don't you think, Like usually a city will have some sort of well accept several designs, competing designs, and then probably well like in Atlanta's case with the seventeenth 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? Uh when um like to two years ago? Really yeah, man, it was a big deal.

Luckily it happened at like four in the morning or five in the morning. But like when you're walking on the bridge, you know the side stuff one whole side fell over onto seventy below, onto the onto the connector right below. Yeah, I kind of remember that. Yeah, but it's an ugly bridge to begin with. Three million. Dude, if you're listening the guy who designed it, I'm sorry, I don't mean to insult your work, but I but do better. It just the city could have done better,

I think. But I think what it came down to, I'm sure it was. All of these are beautiful, but we're just going to spend the money on this one, you know, or whoever got the biggest kick back or wherever that came from, not to be cynical. Living bridges. Yeah, we're talking about that. Um. If you go to northern India to the here we go, uh, 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 from monsoons. 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 plant on the other side into the ground and this is now a

natural tree root bridge. Right, it's like giant living bonds. I like you're they were training routes to go a certain way, and they would take a um, a tree, a felled tree, and split it in half and use that as the guide. Right, it's like the structure so that 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. And I get the impression it's, um, the whole town's responsibilityly, some people in the town's responsibility to make sure that if you see your route starting to go down in the wrong place, you just pluck it up and put it back on a fell log that's guiding it across the way. Yeah, it's pretty neat, like it requires patients obviously, but it also um, I imagine just once a day someone walks down and it's like yep, looking good, and

then just walks away again, pets. The bridge says, keep growing, I'll walk across in ten years, buddy. And apparently those things can last up to fifty years or the the largest one that they have up to a hundred feet, which is thirty meters for our friends in India. Um, and it can bear the way to fifty people and last up to five years, not fifty. That's what I said. Oh, I thought you said people, well, it's crazy, like you gotta google these things. Yeah, they're very pretty, very pretty.

It looks very um dark crystally. Oh yeah, totally, you know what I mean. But they're not unsettling at all like the dark crystal right, which, by the way, if you're ever in Atlanta, sometimes people say, Hey, I'm coming to Atlanta. What should I do? Uh, go to the Center for Popetry Arts and just look at their free exhibit, which includes a full size Skexy. It's terrifying. Yeah, they have We've talked about this before. They have emmett Utter.

For me, that was pretty pretty magnificent. It meant a lot for Emma Utter to meet you too. They're doing Actually I saw it was just at the Museum of the Moving Image and Queens. Oh, yeah, I saw you post something about that. Yeah, they have a Madman exhibit right now, which is pretty neat, but it was they I was not there in time for the Jim Henson when they're they're putting that in place, I think for later coming coming. What's good You didn't miss it yet? Well, yeah,

I'll just go back. We went to the Yoko on No exhibit at Momah. 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 wasn't three. I love that stuff, so I recommend that as well. I'm not a fan of her music, though, I actually got turned onto her music in the listening room there Plastic Band. It's crazy. It's weird stuff, but I kind

of like it. I mean, she's definitely one of 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 sixties, like the early sixties. Yeah, and talk about weathering criticism and still just being like screw you. Yeah, I'm Yoko. Oh No, I don't care

what you say. Well she was exonerated to recently, remember Paul McCartney came out and said like, it was not Yoko owner that broke up the Beatles and saying that it just took him like fifty years to come out and say it. Yeah, she's like, would it kill you? Right? He told me privately many times, but we'll press release, tweet it alright. So we talked about compression and uh

tension being the two main forces. Uh, there are quite a few other forces, dozens even they can act on a bridge in a negative way, And the scariest one, for my money, is torsion. Um. If you've ever seen the video, it's a very famous video of the bridge, what is it the Tacoma the Tacoma Narrows Bridge to coma narrows bridge when it looks like a wet noodle

twisting in the wind, Yeah, it was. 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 bridges 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 I continude walking on it in a car. Yeah, and a guy

ran there was a dog. There's one car in there and there's a dog trapped in the car, and some guy ran and got the dogs. Yes, pretty great heroic stuff. Sure. Then later on I don't know if he'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 is falling into the river, but the section they're walking still swaying way from the bridge. Step back from

the bridge, man, So that's torsion at work. Yeah, and that's a big problem that designers a suspension bridges face because you have a deck that's being held from being held alof by cables. Right, it's not like fixed to anything below it necessarily mean it's 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.

So if you have a swaying 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 into which is sheer. Yeah. Well that's the other awful thing that can happen. It can just snap, well not snap, I guess, but just breaking to two parts. Yeah. Well,

I mean snapping is the result of compression. Sharing would be what it's called technically, where to the same span of bridge has the two opposing forces acting on it at once, UM, in opposite directions, and it goes it makes that terrible sound. Um. If you want to combat torsion, UM. Many ways to do this, You're you're probably gonna have a deck trust going on to help out. Trust saves the day that trust saves the day you're gonna have.

You're gonna do wind tunnel tests if it's a modern bridge beforehand, well you're gonna make a model, yeah, and do tests and see like how does wind affect this bridge and what do we need to do. But the thing is with the um with the Tacoma Narrows Bridge in particular, they did tests. They had that thing rated with standing winds up to a hundred and twenty was an hour. But the winds that day that brought it down.

We're only forty miles an hour, And for a long time they were like, what happened, and somebody said, you know what it was? It was mechanical residence. It was. Yeah, the deck trust was not sufficient for the span that was part of it and the way that the wind hit it and the angle calls the final thing that you just mentioned residents, which is um sort of it's a vibration basically that gets out of hands. 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 has a certain frequency um where it will really pick up force, really absorbed force, it will run through it. Right, So let's say that your bridge um has a residence. Uh, that's like at a frequency of ten. That's probably a total the 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 fort at just the right angle and it makes it sway at a frequency of nine, Well, that bridge is gonna be It's just gonna sit there and sway. Not a big problem. If that wind hits it at just the right angle at just the right speed it's and it starts swaying at eleven, it's still not quite a problem.

But if it gets it just right and it starts it swaying at ten, all of a sudden, those sways are going to become more and more pronounced because all that energy is flowing through at its maximum potential and at its freest flow, because it's hitting the bridge at its natural residence, right. 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 because it's just happening.

It gets worse and work exactly. And that's that's because it hit it at just the right frequency. Yeah, they like in it in the article, which I think is pretty uh down to earth, the snowball rolling downhill exactly. It just keeps getting worse and worse, and that you can't stop it. So but isn't that bizarre that you a bridge has a natural residence and 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 gonna encounter from an earthquake or from winds or whatever. 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, whereas I know all of the wind in the area and the ground movement from an earthquake is going to make it vibrated a free quency 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 deck

plus a and that way the vibration. When you have these overlapping plates and smaller sections, it's gonna create enough friction to disrupt that frequency. Right, it'll change the frequency that the bridge is moving at. But I mean, and not just bridges, to you have to take this into take into account like airplanes, right, you can't use engines on airplanes that create vibrations at a frequency that's at

the natural resonance of the airplane body. Most the airplane body is gonna come apart just from turning the engines on. Could you imagine seeing the airplane wings starting to flap like harder and harder, Right, But apparently the more common thing when you have a disaster catastrophe from a residents a mechanical resonance problem. Um, it's like one bolt, it's like I can't take it anymore and stops, and then that leads to a cascade of failures that aultimately has

the bridge coming down. Interesting. I think that's fascinating. I had no idea that you had to worry about frequencies and vibrations. Why all the bridges you've built of collapse? They collapsed pretty easy. Well, if you've ever heard the old they go down like a French boxer. That means I don't need um. But it was a glass Joe reference. Remember him from Tyson's punch out, Oh No counter He says he was French glass joe. You said, a glass jaw and he went down just like a sack of potato,

so easy. 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. 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 stay all that like an army marching across the bridge and step can cause enough vibration to take down that bridge. It's true

that could happen. So if at the right frequency, right yeah, and 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 on that Time magazine slide show where that happened. Um, there were there were a pair of skywalk bridges inside the Higher

Regency Kansas City Hotel, um in the lobby. They were just like you know, raised bridges going through the lobby, and they collapsed and killed like a bunch of people because people people marching dancing. They were dancing on the on the skywalk. And you think, like up to today or yesterday when I started researching this right, Like, I just thought that's weight or pressure, something like if everybody's dancing, didn't It never occurred to me that the rhythm had

something to do. Yeah, i'd always heard that, Well, you're far more advanced than I am a 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 knowing nothing. And consequently, I think Lina Richie had to change the name of that song because of the accident.

I think originally it was what a feeling when you're dancing on the skywalk and he had to change it to ceiling and everyone's like, that's weird dance on the ceiling, but it rhymes, and he's like, yeah, but nobody ever died from dancing on this on the ceiling. I guess the final thing we should mention is that weather. Um, obviously we'll play a big impact. We already talked about wind, but um, over the years, the materials they use in the design is gone in to take account things like

wind and uh what sun damage. I don't know what I think get the free stall cycles, huge salt salt exposure. If it's going over like a salty body of water, that makes sense. Yeah, there's a lot of things that are trying to bring a bridge down. Nature abhores a bridge basically as much as a vacuum um. I've going what's got. There's probably around six hundred and thirty thousand bridges in the US alone, because there were six hundred and seventeen thousand, nine hundred and thirty five and a

two thousand two census, and they add them. They were adding them at about a thousand a year, maybe nine hundred a year. That's just the US. The world's longest bridge completed in two ten, the Danyang Coon Shawn Bridge. I think I've seen pictures of that. It serves as a railway bridge for the Beijing and Shanghai Railway. It's a hundred and two mile long bridge that's nutty over water. I'm a big fan of cities with multiple water bridges.

That's why you liked Pittsburgh, Pittsburgh, Portland, Budapest. I'm a big fan. Atlanta. Doesn't mean we have bridges, but it's not like you have to go to the Chattahoochee River Lakes. Nobody goes to the Chattahoochie You know what. Um, I got one more thing I want to shout out to PBS is build it big website, which is like beyond nineties as far as websites go. But it was extremely helpful and understanding the forces that work on bridges, different

types of bridges, different specific bridges. Great website and thanks to Adam. I guess you got some information from him. Yeah, thanks Adam. Was he into talking to you about it? Or was he on the other end going oh my god, justsh shut up and watching Tim and Eric? He was he was into talking about it. I figured he would be yeah. Uh. And I actually have to shout out to you mean too because I told her we were building bridges, or well, we were talking about bridges. She

sent me a bunch of stuff on popsicle bridges. Um, apparently there's a a Indie Go go for the world's strongest or Canada's strongest popsicle bridge. Yeah, they're trying to build that. Yes, and they start six screened already for out of popsicle sticks. Good for them. So that's everybody getting shouted out to all over the place in this one. Huh, that's nice stuff. Bam. If you want to know more about bridges, you can type that word into the search part how stuff works dot com. And since I said

search parts, time for listener mayl. I'm gonna call this. I got a couple of street gang responses. Will read over the next couple of shows. Um, 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 worked for a hospital based program and we see every gunshot wound victim and stab wound victim who comes through, which is about four year UM, and about

ten percent of those are gang involved. How you guys have mentioned how you found the number of gangs to be hard to believe, but I think you may you thinking the street gangs is one entity that has strict borders and lots of people. And 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, eight percent of the gangs in the city have less than ten members and have ten to nineteen 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 Arianna. 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, Ariana. We appreciate that email. And yeah, keep them coming. We wanted them more about gangs. I just had the impression the whole time that like one or another, we were officially or unofficially misinformed. H And also let us know who's the coolest famous person you've ever met? You can tweet to us that that's why sk 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 how Stuff Works dot com and has always joined us at our home on the web, Stuff you Should Know dot com. For more on this and thousands of other topics. Is it how stuff works? Dot com