So my culvert/dirt bridge over my creek has washed out 3 times this summer. We had 3 major floods, and each time the water completely covered the bridge, clogged the 2 18" culverts and then removed most of the dirt and one of the culverts this last time.
I'm finally going to build a real bridge, so as to not wash away. My family owns a metal shop, so I'm getting 3 I-beams for the span from them, 16' long each. They should according to my calculations handle 8000 lbs of single point weight in the middle of the span, with acceptable deflection (< 0.75"). I have a 2038r which is 2500#, but by the time you add ballast, loader, me and max loader load is ~6500#, and I wanted some extra margin above that. Extra capacity would be needed if I get stuck on the far side again and need to call my brother to pull me out with his 4066r or H1 Hummer. I plan to have each of the 3 beams get a ~2-3' long pipe welded to each end. Then I'll dig a hole for each in the bank and pour concrete to make sure it doesn't move. Then I was thinking of using pressure treated lumber for decking boards that I attach to the beams with U-bolts. Any advice on what size boards I should use for the decking? I was thinking of making it 8' wide as much lumber comes in 8' or 16' increments, but at 8' that would be the exact width of the H1 and pretty tight for the 4066r (wide tire setting, and 4" spacers) so maybe I need to do 10'. But that would also mean that the tires on most of these wouldn't be right above the beams anymore, so I'd need to make sure the decking could handle that weight. We know metal & the math to make sure we get it strong enough, but I'm far less sure on the wood side. Also is there any type of wood I should favor over another? While it does flood potently a handful of times per year, the majority of the time it will be 3-4' above the water level. The actual creek width is 10-11' where I would be spanning it.