There are 3 basic bridge types
BEAM ARCH SUSPENSION
A beam is simply a horizontal
structure supported at each end
You're in the middle of a forest and you have to cross a stream.
can you do? Cut down a tree so that it falls across the stream.
A couple of #6 blocks form this beam bridge
Adding some #2 blocks and now we have a deck for our bridge
Here's another beam bridge. More complex than the others, but still just a beam bridge.
But look what happens if we push on the end of the bridge.
Now if we add a pair of #4 blocks diagonally, the bridge will stand.
We've built a truss bridge.
A truss is a type of beam, made of lots of smaller
pieces (called members) arranged
so that some of them form triangles.
The Sellwood Bridge was a deck truss. (The deck was on top of the truss).
The Hawthorne Bridge is a through truss- ( the deck, and the cars, go through the truss).