Bridge Building 101

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I’d never built a bridge before, but I sure needed one to get my tractor to the other side of the creek.  I thought this would be a huge project, but I ended up knocking it out in a couple weeks working a couple hours in the evenings.  Here are some pictures showing the build.

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Took awhile to find a good spot to put the bridge.  Tried to find an existing trail that the tractor could take down the ridge that met up with a flat area at the stream.  The stream is about 5′ wide and feeds the pond about 100 yards down.  Since I have control over the water level in the pond, I don’t really have to worry about it flooding and taking the bridge away.  Here ar esome deer I saw sleeping at an burn pile area on the drive down.

 

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This is the path I ended up finding that goes all the way down to the stream.  The grass is all about 6′ high here, so it was a little hairy getting down there without driving into a hidden ditch.

 

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Assembled the basic frame up at the barn (where I have power).  It’s about 5.5′ wide and 12′ long.  The side beams are 4x6s, and the entire frame will sit on 2 additional 4x6s which sit on anchored concrete blocks.  I ran some numbers based on the weight I want it to carry (2 tons of tractor) vs the load strength of doug fir, hence the doubling up.  Since all the weight will be right over the main beams, there wasn’t much need to put huge supports through the middle or across it.  That is all just basic decking joists.  You might notice my SBR sitting off on the side there.  My neighbor was complaining about raccoons around, so I kept it nearby in case they showed up.

 

These pictures show the process of digging out some of the dirt and placing the frame/getting it leveled.  Not much magic here, just a lot of digging and moving.

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Once the frame was anchored down, i threw some decking on using boring old 2×6 doug fir PT and outdoor screws.  It ain’t gonna be pretty, but I’m not spending 3x for actual decking screws and lumber.  At this point in the project, Charlie began running full speed across the bridge, until she slipped and flew into the creek.

Once the bridge was done, I came up with this way to join it to the earth so I could actually drive up on it, without dirt touching the wood.  This ended up working way better than I thought it would.  I also put those handy rails on the side, so my tractor wouldn’t fly off.  The bridge is only 2″ wider than the wheelbase, so some safety was required.

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Tah-dah.  The first drive across it was a little terrifying.  It’s since survived quite a few drives and hasn’t cracked/buckled/shifted.  It’ll be interesting to see how it survives the next few years.

 

If I were to do this over, I’d make it 16′ long, keep the concrete supports where they are now (spaced 12′), and add additional supports at 0 and 16′.  Even though the creek was only about 5′ wide, it would be nice to have the ends safely away from any possible erosion or settling.

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Bridge Building 101

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