How are bridges built over water? Hi, welcome to Curious Kids Everyday. I'm Josh. How are you doing today? It's so good to hear from you. Hey, has your family ever driven over a really long bridge? Did that bridge go over the water? I've been on a really long bridge before. There's this city in Florida. At the top of the state. It's called Pensacola. They have a bridge there called the Three Mile Bridge. I'll give you one guess why it's called the Three Mile Bridge. Yep, it's over three miles long. Have you ever been on a bridge that was three miles long? Every time I go over that bridge, I think about how crazy it is that people actually built this thing. That just seems impossible. Have you ever stood under a huge bridge? It's just amazing, isn't it? Can you imagine a bridge being built on water? How do they do it? Well, if you want to know how they build bridges over water, we're going to have to learn a little engineering. Let's do it. Building a bridge over water seems impossible to me. I mean, the water is always moving. The ground under the water is very hard to reach. Workers can't just stand in the middle of a bay or a river the way that they can stand on a bridge. They can't just stand in the middle of a bay or a river. They can't just stand in the middle of a bay or a river the way that they can stand on dry land. So, how do they do it? Do they park their boats under where they want the bridge to be and just start building? No, that doesn't make sense. Engineers start by very carefully studying the place where the bridge is going to go. Engineers are people who figure out how to build things safely. That means they have to keep a lot of things in mind when building a bridge over water. They need to know how deep the water is, what the bottom is made of, how strong the wind can get there, how do the waves move there, and they have to determine how heavy the bridge is going to be. They also need to think about things like hurricanes and earthquakes depending on where the bridge is. Now, one of the most important parts of a bridge is the foundation. The foundation of a structure is what supports everything above it. For a bridge over water, that means building giant supports called piers. You know those big long things coming out of the water that go all the way up to the top of the bridge? Yep, those are called the piers. A pier is a big upright support that holds up the bridge deck. Oh, do you know what a bridge deck is? That's the part of the bridge that the cars drive on. Anytime you drive over a bridge, you're on the bridge deck. The bridge is a bridge that goes all the way up to the top of the bridge. The bridge is a bridge that goes all the way up to the top of the bridge. Okay, but how do workers build a pier in the water? Well, this is where things get crazy. Sometimes they use something called a cofferdam. A cofferdam is a big temporary enclosure built in the water around the place where people need to work. After the walls are in place, workers pump the water out from inside of it. So it's kind of like building a big fence in the water and then sucking all of the water out of the fenced in area. That gives the workers a dry place to dig and build, even though water is still all around them. They've just pumped it all out of this one specific spot. And once they have all that dry space, they can create the foundation they need for the pier. That's where piles come in. Do you know what a pile is? A pile is a long, strong post made of steel or concrete. Special machines hammer or drill them deep into the mud or the sand or the rock below. The piles reach down to stronger ground and help hold up the heavy structure above. But they can't always use cofferdams. Sometimes the water is too deep or the area is too large and it would just be too difficult to block the water out. And when that happens, workers build right in the water instead. They can drive piles down from big machines on boats, pour special concrete that hardens underwater, and even send divers down to help guide things into place. Sometimes they even build large pieces somewhere else and then float them into position and carefully lower them. Once the foundation and pier are ready, crews begin adding the parts above the water. They may bring in enormous concrete sections or steel beams by barge. Do you know what a barge is? A barge is a big, flat boat used to carry heavy things, like steel beams. And then cranes are used to lift the pieces into place. Then the bridge deck is built across the supports. Do you remember what we said the bridge deck is? Yep, it's the part you drive on. And after the bridge deck is built, then all the usual road stuff is added, like guardrails and pavement and lights and all those things. Bridges over water have to be extra strong because they have a lot of forces acting upon them. Wind pushes on them and saltwater can wear materials down over time. Boats may pass underneath, and also heavy vehicles are on the surface of it all day every day. That's why engineers use strong materials like steel and reinforced concrete. Reinforced concrete is just concrete with steel inside of it to make it stronger. And that is how bridges are built over water. Okay, let's have a quick quiz. What is the flat part of the bridge called that cars drive on? It's called the bridge deck. And what do engineers call the strong upright supports that hold up a bridge? They're called piers. And what is the temporary wall built in water so workers can pump the water out and work in a dry space? It's called a cofferdam. And what are long, strong posts driven deep into the ground under the water to help hold the bridge in place? Those are called piles. Let's play true or false. True or false. Engineers study the water and the ground before building a bridge. That is true. True or false. Workers usually build water bridges by floating the whole finished bridge on top of the water and leaving it there. No, that's false. That would be pretty impressive if they could do that. That would be a very big barge. True or false. A barge is a kind of boat used to carry the bridge. True or false. A barge is a kind of boat used to carry heavy materials. That is true. Would you rather build a bridge or build a building? Well, now that I've learned so much about building bridges, I would love to build a bridge. I'd love to go down to a lake near me and just build a bridge to one of the islands that is out in the distance. It'd be fun if we didn't even have to use a boat to get to those islands. We could just build a bridge to the island. Alright, I've got a round of what am I? What am I? I am only there while workers are building. I keep water out of a work area. And my name kind of sounds like this. What am I? It's a cofferdam. A cofferdam. And speaking of cofferdams, aren't those things so cool? Think about it. You're basically building a temporary dam in the water just so you can build a foundation in a dry space. And big bridges, long bridges, they need lots of foundations. But thankfully, even if a cofferdam isn't possible, engineers have other ways to build those foundations to make the bridge deck safe for you to drive over. Bridges are an engineering marvel, and bridges over water are even more so. Now that I've learned how they're built, I'll be thinking about it every time I drive over a bridge. Pretty amazing. What kind of question do you think we'll ask tomorrow on Curious Kids every day? I can't wait to find out, so until then, keep asking questions and stay curious kids. And we've got a few birthdays today. Today is Sterling's birthday. Sterling is from Texas, and Sterling is turning seven. Happy birthday, Sterling. Corey Jude is from Georgia, and Corey Jude is turning six. Happy birthday, Corey Jude. Mia is from New York, and Mia is turning six. Happy birthday, Mia. River is from Nebraska, and River is turning seven. Happy birthday, River. And Zonviev is from Illinois, and Zonviev is turning nine. Happy birthday, Zonviev. To all the grown-ups listening, if you're a Curious Kid once their birthday mentioned on the show, please visit supportcuriouskids.com and join the Curious Kids Club. That's supportcuriouskids.com. See you tomorrow!
