The Beam Bridge

Beam Bridge - a simple sketch

simple sketch of a beam bridge
simple sketch of a beam bridge

A Beam Bridge is the simplest design for crossing a distance.

It consists of a horizontal beam supported at each end by piers. The weight of the beam pushes straight down on the piers. The farther apart its piers, the weaker the beam becomes. This is why beam bridges rarely span more than 250 feet.

Modern Beam Bridges

Qiantang River Bridge
Qiantang River Bridge
Feiyun River  Bridge, Zhejiang Province
Feiyun River Bridge, Zhejiang Province

Load and Thrust

load and thrust
load and thrust

Load and Thrust

 Load is a consequence of gravity and always acts vertically.

The ground exerts an equal and opposite force upwards on the weight. This force is called thrust.

a weight on a beam
a weight on a beam

 When a weight is placed on a beam it exerts a load. However, the weight is not directly in contact with the ground.

Hence the load reaches the ground by passing along the beam and the down the piers as shown in the diagram opposite.

Advantages of a Beam Bridge:

  1. easy to construct
  2. relatively cheap


  1. cannot span great distances

If the deck is supported by a number of beams instead of just one then it would be easier to erect and easier to fix.

beam with a load
beam with a load

As a bridge is loaded, the beam bends in a downward direction - sag. When the beam bends, new forces are imposed along the length of the beam:

The top of the beam is compressed (shortened)

The bottom of the beam is tensioned (pulled apart).

As you can see from the diagram, the lines mark equal distance on the beam and the angle of these lines converge at a point above the beam.

Testing to destruction

 General rule: material breaks far more readily when it is under tension the when it is compressed.

Elastic Substances: materials that deform under a load and then returns to its original shape when the load is removed. Steel is slightly elastic

Advantages of Elastic Substances:

  1. when exposed to a massive load they will deform before collapsing entirely
  2. they give warning (visual inspections can determine if buckling has occurred)

The Bridge Challenge

Comments 67 comments

Waren E profile image

Waren E 7 years ago from HAS LEFT THE BUILDING............

Hi nice hub on architecture ,have you started using CAD programs yet? If so which one ,"auto cad" perhaps!

lydia_rae profile image

lydia_rae 7 years ago Author

no I haven't I have no idea how to get it but I deffinately need to start. thnx for the comments :)

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Hi all Beam Bridge

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How is Kylee going to get killed? And why?

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wow you kids on here are kinda sad...

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me and my primary friend commented on this along time ago, he moved somewhere else :D


Bob 3 years ago



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abdu m 2 years ago

it is so short

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