sanity check my bridge design

LouNY · Sep 7, 2018

If you are concerned about the load capacity of sistered planks I would seriously consider sandwiching a custom angle or t steel in wood a 4 " topped 8" strap making a 4x8 T sandwiched with 2x10's and topped by a 2x6 would make a very solid beam.

newbury · Sep 7, 2018

Can you find a used flatbed trailer frame to park across the span? Then just "sister" some beams on the side.

Rustyiron · Sep 7, 2018

tractchores said:
I’d like to, but I think it uses creosote soaked railroad ties (12x12) with just 2 stringers. Can’t get those anymore that I know of. I like the idea of putting a wood wrap on a steel beam though it’s probably not realistic. Fines are unlikely, but large!

A lot of Hemlock (un treated) is used here in N.E. for forestry bridges, I suspect very similar to yours. We're not far from each other and I can buy hemlock for .50c a board ft. That's $6 a foot for a 12 x 12. If you have the luxury of a little time, (and no inquisitive inspector) you could "paint" them with old motor oil for a little added protection. I am leery of today's common treated lumber. There is a grade of treatment that is used for wharf's & such that is only available in timber sizes and not your retail outlet type material. I'm not sure where you'd source them from but with all the shoreline around here, it shouldn't be too hard to find.

tractchores · Sep 8, 2018

Rustyiron said:
A lot of Hemlock (un treated) is used here in N.E. for forestry bridges, I suspect very similar to yours. We're not far from each other and I can buy hemlock for .50c a board ft. That's $6 a foot for a 12 x 12. If you have the luxury of a little time, (and no inquisitive inspector) you could "paint" them with old motor oil for a little added protection. I am leery of today's common treated lumber. There is a grade of treatment that is used for wharf's & such that is only available in timber sizes and not your retail outlet type material. I'm not sure where you'd source them from but with all the shoreline around here, it shouldn't be too hard to find.

Thanks. Property is in northern Maine so I’ll have to ask around to see where I might get something like that. The snowmobile and atv guys make bridges the same way so they may have a supplier.

tractchores · Oct 10, 2018

Finally did my project. After talking to some locals I found out my stream is man made (naturalized drainage ditch dug 50 years ago). The good news is that made a culvert legal. After pricing both options I did a 24" diameter culvert 16' long. It came out good, we'll see how it holds up in spring. I put rocks on each end and backfilled with bank run gravel mixed with dirt (only thing available in that area). A little cheaper than the bridge and should last longer.