Bridges Part 3: The Pratt Truss / Ponts a Treillis Pratt

The bridge I'm going to show this time is a Pratt truss which is very similar to the Howe as far as the Polydron pieces are concerned.

In the kit, it looks like this:

My Frameworks version looks like this:

If you happen to have solid square pieces, it's nice to use them for the deck as I have in the above picture, but it's not absolutely necessary. However if you have only Frameworks pieces, you might want to add a piece of stiff cardboard on top of the deck in order for the children to drive their toy cars on the bridge.

 

For this bridge you need:

2 plinths (see previous post here)

      20 equilateral triangles

      8 squares

Bridge

      20 right angle triangles

      12 squares or 6 frameworks squares and 6 full squares

 

Here's the flat layout of the above bridge:

 

 

Here's the flat layout using only Frameworks pieces:

 

 

 

In the Polydron Bridges kit they add rectangles at each end of the bridge for stability because without them the bridge will lean.

 

Because my plinth construction is slightly different, you can't use rectangles, so I've added squares instead:

Pictures of real bridges:

In Iowa

In North Dakota

 

Links:

Truss bridges on Wikipedia

Pratt trusses on Garrett's Bridges

 

En Francais:

Ponts a treillis sur Wikipedia

Ponts a treillis sur Gramme