How Do Forces Act on Members in a Pratt Truss Bridge Design?

[giacomh]

Homework Statement

I'm designing a pratt bridge for class that looks like this:
http://www.garrettsbridges.com/photos/pratt-truss-bridge/attachment/pratt-truss-bridge-2/

I have a two dimensional drawing of one side of the bridge.

2. Homework Equations / 3. The Attempt at a Solution

All of my horizontal members on the top are in compression and the bottom are in tension. All of my vertical members except the first one one each side are in compression. My diagonal members vary between tension and compression depending where the weight is placed. Is this possible?

 

[pongo38]

Yes, but it depends on the loading. The end diagonals joining the supports would be in compression. Otherwise I would expect tension in the vertical plane diagonals. Perhaps you need to reword the question or provide evidence for your belief.