How are bridges built on rivers?
18th December 2017
Why do we build a bridge ? A bridge is built to cross an obstacle, that a car or a person cannot pass easily.
Have you ever built a bridge? Maybe a pretend bridge with pillows from 1 couch to another. Or ran across a bridge in the playground !
It takes a lot of work to build a bridge ! One of the simplest bridges ever made was to cut a tree and fell it across a river to cross it. Bridges have come a long way since then.
First the planners have to go and check out the location and get answers to important qeustions.
What kind of area it is, is it rocky or wet or sandy etc.
How much weight will the bridge have to bear ? Will only people walk across it or cars, buses or even heavier- trains!
Does it have to be a long bridge or a short bridge ?
Then the architects and engineers design the bridge on paper and make models of it.
Most bridges have a foundation build inside the bed i.e the bottom of the river under the water, over which they will run.
But how is the foundation built under water ?
A small wall is built around part of the river where the foundation needs to go. Water is pumped out of it and the foundation is built.
Water does not have to pumped out of the whole river! Nor do workers have to work underwater! Only water inside the small part inside the wall is pumped out and engineers can dig on the ground under the river to build the foundation.
Once that is ready pillars are built on it and the bridge is built on top of the pillars.
The 3 most common types of bridges are:
Arch bridge: This kind of a bridge was usually built in olden times. The bridge is rests over large stone arches.
Beam bridge: A simple straight horizontal beam supported by pillars.
Suspension bridge: Long cables are used to suspend the bridge from pillars. This is the best bridge if you need to cover long distances. It can be built from 2000 to 7000 feet long!
Activity: Join the dots in sequence to build the bridge.
How are bridges built ?
- Try your hand at building a bridge from Pre-k pages.
- Read this answer from Quora to get more details on how bridges are built.
- Watch this very informative video to see how bridges are made.
- Read some of the below books to learn more about bridges.