Would like to build a concrete cattle guard frame.
8'x15' bottom, 3' sides
I plan on using I-beams running across the 8ft portion and lay pipe running across these I-beams for the 15ft width. I would like for the I-beams to rest on a lip within the sides. In other words, the sides would be stair stepped and I would place the I-beam on the step instead of the floor. My problem is I can't figure out how to build this step/lip. I am assuming that the floor would be poured first by itself. How do I form this stair step/lip for the I beam to rest on? Thanks very much in advance.

The ledge for the cattle guard is the same as a brick ledge. The trick is to create a 6: thick stemwall with a ledge on the inside face that will support the grate. This can be easily done with a 2x4. The web site below shows how it is done using a cardboard form designed for this purpose. By the way, I have seen cattle refuse to cross striped pavement done with paint lines (kind of freaks them out). I prefer using gates with horses because of the injury potential with cattle guards.

For the figure in the link below, focus on the profile schematic in the upper left corner. If using wood, oil it so it releases, and drive screws from the outside of the forms. If you don't get it, post back.

http://www.surevoid.com/surevoid_web/product/brickledge_w.html