Question
I need to build a foot bridge to connect two properties. The clear span has to be 20 feet. Do you where can I find the information I need to build this bridge ?
Thank you very much.

Answer
Here i a guide for a site-built wooden foot bridge that may work:  http://www.ronhazelton.com/howto/footbridge_over_creek.htm  Increase the beam size the longer the span.  Be sure and install the railing, for pedestrian traffic.

IF you need to drive a car or truck across it or it gets longer than about 25 feet, I have used refurbished rail flat-cars - an old rancher's trick.  Here is an outfit located in Central Texas, but if you look around in your area, you may be able to find a closer source.  (they have neat pictures!!)

http://www.flatcarbridge.com/

You'll need concrete abutments to make sure it doesn't go anywhere, but the cost is moedt, compared to an all-new steel structure.

Hope it helps.  ~Marc