4 foot concrete bridge

[MELOC]

i have a seasonal / flood run that i need to bridge. it is about 4 feet wide. i thought of pouring a concrete top. how well do i need to reinforce the concrete and how thick to span 4 feet. i will be driving over it with a truck hauling firewood.

[ericjeeper]

If you are having concrete delivered you will likely have atleast a 3 yard minumum. or are you planning on mixing the concrete by hand?
Four feet is not a very large span. Are you sure this will be far enough back onto the banks to be clear of future erosion? I am guessing you will be building this bridge atleast 9-10 feet wide? If it was me, I would build it eight inches thick with a nicely laid out mat of #5 bar six inches on center each way,making sure to keep the matt about two inches up off the bottom of the form using concrete bricks or "chairs" , Even at 4'x10'x8" you are still only using one cubic yard of concrete.
Back in my younger days I built bridges for a living, but was never the engineer.But most of the pour in place bridges we built were eight inches thick,and spanned 12-16 feet between bents. I would be certain to build some sort of pier-end section that ties it down into the soil or rock if available. just to keep your investment in place

[MELOC]

my plan was to line the run with rock and mortor on the sides. or more simply to build some crude bearing walls and put a concrete span on them. i had planned on some sort of reinforcement but was uncertain about the thickness of the slab. the slab will probably be six feet (4 foot span and 1 foot each wall) by 8 feet wide.

i thought of just putting in pipe and filling with gravel but i have no big culvert pipe. i would be afraid if we got a real flood it would wash out.

[rambler]

8' wide looks _real_ narrow when coming up to it with a vehicle..........

--->Paul