Building a Bridge?

[TomSeller]

Years ago I built two bridges of that size with old creosote timbers from a dismantled train trestle. The larger vertical dimension is an advantage in strength when it comes to supports. It could be that a 6x6 is not going to carry near the weight of a 12x2, without looking it up I am not positive.

 

[rd_macgregor]

I like the idea of using an old trailer frame. I tried tracking down a flat bed shipping container (just like all other shipping containers, but without the top, sides and ends), but they are pretty rare here. Maybe there is a source of shipping containers in Houston? If you have a cutting torch, you could even cut down a regular container and end up with a 20' steel bridge with 38,000 lb. capacity; I don't think it would float away in high water, either.
BOB

 

[Bigkrank]

Why can't you just put a pipe in? I got a 5 ft dia pipe dug out of an interstate highway project cheap years ago. Got some dug out from an abandonded railroad a few years back.

 

[LD1]

Dont use 6x6 beams. Waste of money and material.

3 2x10's laminated together is almost double the strenght. And 3 2x12's is about 2.5 times stronger. And either would only be a little more in cost.

Either way, for a bridge I like steel. Its more predictable and it certainly wont float.

For the decking, if you only use 2 beams, you want more than 2x lumber. A tractor will crush right through it unless you keep it perfectly over the beams.

Another option....and its wood and dont cost much if avaliable.....

Contact your local power company. Mine gives away broken and free poles. My bridge in the woods is nothing but electric poles laid down and butted up tight to each other. Like a raft. And then decked with 2x lumber just to keep them from rolling appart. You would have to find a way to anchor it down though...

 

[schmism]

look for an old semi flatbed on CL. sometimes you'll find a contrainter trailer frame. either one are great for useing as bridges as they are built to hold significant weight and can span 20-40' depending on lenght

 

[MotorSeven]

5-6' deep and 8' wide is a perfect candidate for culverts. Here it is common to place several in a row, then pour concrete over them & level it out. That way when it floods out of the bank & over the culverts it does not wash them away.....works perfect.