Friday, 4 March 2016

Weekly Wrap UP--Truss bridges 3/4/16

MarioFan and I are continuing to explore and build the many different types of bridges found around the world.  So far we have looked at beam, arch, and suspension bridges. This week we are looking at Truss Bridges and understanding which shapes are stronger and why.

A simple experiment is to use popsicle sticks and binder clips, and make a square and triangle.  I then ask MarioFan which shape was the sturdiest.  While MarioFan was able to (without removing the clips) change the square into a diamond shape easily he was unable to change the shape of the triangle.  This happens because of  what engineers call the degrees of freedom.  The square truss has one degree of Freedom, which means it can move or rotate in one direction, the only way to stop this is to have very, very strong joints.  The triangle on the other hand has zero degrees of freedom, which means the joints can not rotate even when held with simpler joints.  We discuss why engineers would want to use which shape and how it effects building and weight of bridges.
Next we got to work building several different types of truss bridges using various supplies.
First we built a bridge using toothpicks and marshmallows

We used graham crackers for the road.  We tried to place a toy car on the bridge but it wouldn't support it.  Then MarioFan ate it:) always the fun part of any school project

Next we got to work on making a popsicle truss bridge --

There are many patterns that can be found on the web, some very complicated and others very simple.  We came up with our own patterns after looking at many many patterns

He enjoyed driving his Mario car over the bridge.   This bridge did much better supporting the toy car 

Next we got out our bridge modeling kit and built another Truss bridge 

and added it to our bridgemodel stand

Then we got out our K'nex kit MarioFan decided to build a K-truss bridge after looking at the many different types of Truss bridges.  

First we built the beam bridge and tested its strength.  He noticed how easily it bent in the middle

We added the Truss beams 

and tried to bend the middle and this time it didn't budge.

Can you see the K's in the beams

Lastly we decided to turn our popsicle truss bridge into a covered bridge after looking at some truss bridges on the web.

MarioFan decided to paint it red.

We had a lot of fun learning about Truss Bridges and understanding why Triangles are a stronger shape and why engineers prefer to use then on bridges.

I just got word that we will be meeting up with a real bridge engineer in the next few weeks and looking at a local historic bridge.  Both of us are excited about this opportunity and looking forward to learning even more about bridges from an expert!


  1. I love this! The models are wonderful and this post reminds me why I love truss bridges so much.

  2. How exciting to put what you're learning together with real life; that's awesome! I must admit that after my son's unit on bridges we spent a fun afternoon in the city finding all the different kinds!