Schroeder and RobA,

Here's a few tidbits on bridge building:

Short bridges... say less than 15', do not need to be especially strong or require huge, heavy beams.

Load capacity of up to 10,000# is easy to build with a great safety margin. Even a 3:1 safety margin will still not require large beams.

You can look at a 20' 7500 GVW flatbed trailer and be amazed at how skimpy it is. Yet, you can block up the ends (wheels up) and drive a 5000# tractor across it without it sagging much.

Treated 2x12's beams and 2x6 decking work just great for short 10 foot spans.

Above 10' but less than 15', a cental post and braces are in order... either straight shoring or suspension are easy to build and work great.

Small bridges rarely fail catastrophically. Most home-made bridges are not high enough to make failure serious if you use your ROPS correctly.

Be warned, there is a huge difference in a 10' and a 15' bridge! 15' and above requires huge beams and/or big steel!

Shrimp