Truss Bridges Lesson for Kids: Facts & Design

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  • 0:04 Strong Triangles
  • 0:43 What Do Truss Bridges…
  • 2:09 Why Use a Truss Bridge?
  • 2:36 Pitfalls of Truss Bridges
  • 3:32 Lesson Summary
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Lesson Transcript
Instructor: Mary Beth Burns

Mary Beth has taught 1st, 4th and 5th grade and has a specialist degree in Educational Leadership. She is currently an assistant principal.

When it comes to building bridges, there are many types to choose from. Truss bridges have been a top choice for hundreds of years. Come and learn about what these bridges are like, their pros and cons, and examples in the real world.

Strong Triangles

What shape do you think is the strongest? Believe it or not, the triangle is actually the strongest shape. Think about it like this: imagine that you have a square, a circle and a triangle in front of you. When you push down on the top of each one, what will happen?

Well, the top of the square will bend and will ultimately snap if you push hard enough. The circle will squish into an oval type shape. What will happen to the triangle? Nothing! This is because the angles of a triangle keep it from collapsing.

This idea is the basis of the truss bridge, which is made of connected triangles.

What Do Truss Bridges Look Like?

Okay, so the truss bridge is actually more complicated than just being made of connected triangles. Many different smaller parts make up the bridge. Here are the basic components of a truss bridge:

Parts of a truss

There are floor beams that make up the bottom of the bridge, also known as the bottom chord. Perpendicular to the floor beams are the stringers, which are long beams that provide significant support to the bottom of the bridge. Laying across the beams and the stringers is the deck, which the road or tracks will lay on top of.

Along each side of the bridge are the vertical members, which are poles going up and down. They make squares of space, also known as panels. There are also diagonal members that slice the panels in half diagonally, so what shape is made? Triangles! This part of the bridge is very important because it allows the truss bridges to withstand compression forces (squeezing together, like when a heavy car drives across) and tension forces (stretching apart, like when extreme weather takes place).

On the top of the bridge is the upper chord made of struts, which are vertical beams that hold together the top of the bridge. Triangle shapes are formed here by adding additional bracing at the top. This additional bracing keeps the bridge from swaying when the wind blows.

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