June 11, 2015 • 56 mins
From prehistoric logs across streams to the 102-mile Kunshan Grand Bridge, nature works ceaselessly to take down spans. Learn about the fascinating ins and outs of bridge design and building and the mind-boggling challenges structural engineers face.
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Episode Transcript
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Speaker 1 (00:01):
Welcome to you Stuff you Should Know from House Stuff
Works dot com. Hey, and welcome to the podcast. I'm
Josh Clark with Charles W. Chuck Bryant with Jerry Rowland
with me Josh Clark, Mr. Stuff you Should Know featuring
Josh Clark's about to say you never introduced yourself and
(00:22):
then you done did it twice three three times? Oh yeah,
you always introduce your but you never say your last name.
I think that's extruct me. John. No, I say I'm
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?
(00:50):
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
(01:14):
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,
(01:36):
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,
(01:58):
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
(02:21):
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
(02:41):
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
(03:04):
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?
(03:27):
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
(03:47):
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
(04:11):
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,
(04:33):
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,
(04:56):
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
(05:17):
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
(05:38):
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
(06:01):
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
(06:22):
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.
(06:44):
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.
(07:05):
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
(07:28):
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,
(07:50):
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
(08:13):
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
(08:33):
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
(08:53):
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,
(09:15):
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
(09:38):
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
(10:01):
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
(10:26):
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
(10:51):
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
(11:13):
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
(11:35):
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,
(11:58):
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
(12:20):
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
(12:42):
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
(13:03):
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
(13:23):
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
(13:46):
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,
(14:07):
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,
(14:31):
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
(14:54):
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.
(15:16):
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.
(15:36):
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
(15:57):
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
(16:18):
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,
(16:40):
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
(17:02):
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
(17:23):
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
(17:45):
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
(18:07):
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
(18:27):
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,
(19:00):
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
(19:22):
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,
(19:43):
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
(20:06):
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,
(20:27):
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
(20:49):
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,
(21:14):
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
(21:35):
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
(21:57):
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
(22:21):
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
(22:42):
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
(23:04):
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.
(23:26):
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
(23:47):
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
(24:10):
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,
(24:32):
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
(24:53):
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
(25:13):
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.
(25:37):
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
(25:59):
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
(26:21):
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,
(26:46):
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,
(27:09):
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.
(27:34):
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
(27:54):
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,
(28:16):
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
(28:40):
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
(29:03):
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
(29:24):
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
(29:44):
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
(30:06):
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.
(30:27):
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
(30:49):
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,
(31:12):
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
(31:34):
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
(31:54):
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
(32:15):
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,
(32:57):
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
(33:19):
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
(33:40):
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
(34:01):
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,
(34:23):
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
(34:43):
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.
(35:06):
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
(35:26):
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,
(35:47):
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,
(36:11):
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
(36:33):
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
(36:53):
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,
(37:16):
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
(37:37):
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,
(38:00):
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
(38:22):
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
(38:44):
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,
(39:05):
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,
(39:27):
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
(39:50):
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.
(40:13):
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
(40:34):
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.
(40:59):
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
(41:19):
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?
(41:43):
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
(42:05):
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
(42:27):
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.
(42:49):
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
(43:12):
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.
(43:34):
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
(43:57):
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
(44:21):
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
(44:44):
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
(45:06):
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
(45:29):
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,
(45:50):
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
(46:11):
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
(46:35):
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
(46:56):
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
(47:17):
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
(47:38):
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
(48:00):
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
(48:22):
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
(48:42):
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
(49:05):
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
(49:29):
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,
(49:50):
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,
(50:12):
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
(50:34):
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
(50:55):
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
(51:17):
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
(51:38):
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
(51:59):
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
(52:22):
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.
(52:43):
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
(53:05):
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
(53:25):
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
(53:46):
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
(54:11):
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.
(54:33):
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
(54:53):
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
(55:15):
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
(55:38):
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,
(56:00):
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
(56:22):
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
Welcome to you Stuff you Should Know from House Stuff
Works dot com. Hey, and welcome to the podcast. I'm
Josh Clark with Charles W. Chuck Bryant with Jerry Rowland
with me Josh Clark, Mr. Stuff you Should Know featuring
Josh Clark's about to say you never introduced yourself and
(00:22):
then you done did it twice three three times? Oh yeah,
you always introduce your but you never say your last name.
I think that's extruct me. John. No, I say I'm
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?
(00:50):
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
(01:14):
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,
(01:36):
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,
(01:58):
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
(02:21):
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
(02:41):
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
(03:04):
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?
(03:27):
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
(03:47):
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
(04:11):
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,
(04:33):
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,
(04:56):
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
(05:17):
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
(05:38):
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
(06:01):
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
(06:22):
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.
(06:44):
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.
(07:05):
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
(07:28):
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,
(07:50):
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
(08:13):
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
(08:33):
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
(08:53):
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,
(09:15):
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
(09:38):
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
(10:01):
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
(10:26):
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
(10:51):
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
(11:13):
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
(11:35):
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,
(11:58):
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
(12:20):
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
(12:42):
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
(13:03):
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
(13:23):
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
(13:46):
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,
(14:07):
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,
(14:31):
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
(14:54):
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.
(15:16):
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.
(15:36):
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
(15:57):
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
(16:18):
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,
(16:40):
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
(17:02):
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
(17:23):
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
(17:45):
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
(18:07):
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
(18:27):
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,
(19:00):
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
(19:22):
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,
(19:43):
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
(20:06):
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,
(20:27):
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
(20:49):
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,
(21:14):
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
(21:35):
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
(21:57):
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
(22:21):
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
(22:42):
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
(23:04):
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.
(23:26):
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
(23:47):
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
(24:10):
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,
(24:32):
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
(24:53):
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
(25:13):
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.
(25:37):
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
(25:59):
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
(26:21):
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,
(26:46):
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,
(27:09):
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.
(27:34):
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
(27:54):
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,
(28:16):
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
(28:40):
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
(29:03):
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
(29:24):
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
(29:44):
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
(30:06):
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.
(30:27):
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
(30:49):
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,
(31:12):
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
(31:34):
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
(31:54):
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
(32:15):
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,
(32:57):
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
(33:19):
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
(33:40):
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
(34:01):
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,
(34:23):
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
(34:43):
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.
(35:06):
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
(35:26):
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,
(35:47):
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,
(36:11):
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
(36:33):
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
(36:53):
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,
(37:16):
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
(37:37):
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,
(38:00):
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
(38:22):
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
(38:44):
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,
(39:05):
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,
(39:27):
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
(39:50):
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.
(40:13):
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
(40:34):
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.
(40:59):
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
(41:19):
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?
(41:43):
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
(42:05):
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
(42:27):
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.
(42:49):
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
(43:12):
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.
(43:34):
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
(43:57):
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
(44:21):
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
(44:44):
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
(45:06):
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
(45:29):
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,
(45:50):
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
(46:11):
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
(46:35):
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
(46:56):
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
(47:17):
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
(47:38):
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
(48:00):
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
(48:22):
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
(48:42):
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
(49:05):
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
(49:29):
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,
(49:50):
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,
(50:12):
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
(50:34):
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
(50:55):
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
(51:17):
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
(51:38):
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
(51:59):
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
(52:22):
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.
(52:43):
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
(53:05):
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
(53:25):
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
(53:46):
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
(54:11):
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.
(54:33):
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
(54:53):
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
(55:15):
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
(55:38):
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,
(56:00):
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
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to stuff Podcast at how Stuff Works dot com and
(56:22):
has always joined us at our home on the web,
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