Wooden bridge for 2000# tractor to cross creek

[bkibler]

I've built a few bridges on my property, mostly from felled trees. But my latest is a 24' span drawbridge built from Werner aluminum staging planks. They're rated for 750 lbs load each, yet only weigh about 100 lbs per span, so easy enough to raise by hand. I added a temporary support mid-span to a large rock in the creek bed that cuts the span to 12', which should double the load capacity to 3,000 lbs total.

This creek drains many square miles, so when ice starts melting in the spring, the drawbridge gets raised to let the water and debris through, and I pluck out the center support with a loader. The bridge is strong enough for my Kubota B7610 w/loader, but mostly sees ATV, log trailer, and snowmobile traffic. (on the left in the photo is an older pedestrian drawbridge, in the raised position)

If you find a painter going out of business, you can get staging for a bargain. It's not nearly as strong as a flatbed trailer or shipping container, but much easier to work with and remove for the inevitable floods.

If you want to see 15,000+ lbs of tractor and camper going over a different bridge made entirely from multiple layers of criss-crossed saplings, check out this video
To be fair...it was a temporary construction span over a marshy swale, not a deep running creek. The 100 or so saplings flexed down about 6 inches from the weight of the trailer, but even if some cracked, the overall structure had enough redundancy to hold the load.

 

[CoyPatton]

That may be appropriate for a roof or floor, but a tractor has a different footprint.

Before building I would double check myself, but memory serves that is for s snow load for a roof. (I believe a 40 psf rating, again I would double check before construction). Also that is a min spec, I seldom build anything to min standards, unless it is temporary and often not then.
Not sure I would trust that ratio for a walking bridge, much less an equipment bridge.

 

[CoyPatton]

I've built a few bridges on my property, mostly from felled trees. But my latest is a 24' span drawbridge built from Werner aluminum staging planks. They're rated for 750 lbs load each, yet only weigh about 100 lbs per span, so easy enough to raise by hand. I added a temporary support mid-span to a large rock in the creek bed that cuts the span to 12', which should double the load capacity to 3,000 lbs total.

This creek drains many square miles, so when ice starts melting in the spring, the drawbridge gets raised to let the water and debris through, and I pluck out the center support with a loader. The bridge is strong enough for my Kubota B7610 w/loader, but mostly sees ATV, log trailer, and snowmobile traffic. (on the left in the photo is an older pedestrian drawbridge, in the raised position)

If you find a painter going out of business, you can get staging for a bargain. It's not nearly as strong as a flatbed trailer or shipping container, but much easier to work with and remove for the inevitable floods.

View attachment 702671

If you want to see 15,000+ lbs of tractor and camper going over a different bridge made entirely from multiple layers of criss-crossed saplings, check out this video
To be fair...it was a temporary construction span over a marshy swale, not a deep running creek. The 100 or so saplings flexed down about 6 inches from the weight of the trailer, but even if some cracked, the overall structure had enough redundancy to hold the load.

I have not watched the video, but having been raised in an area that was reclaimed swamp land, your description is of a log road. In gone-by years, these were common construction through wet lands.
Log roads are still common in logging operations in wet areas, but as a temporary solution for the logging, not usually left. I have also know some folks that have done these in muddy areas of their own property, but usually for ATV trails for hunting.

 

[Everhard]

I made my bridge 8 years ago, took a couple large trembling aspen trees to make the 2 main logs (maybe 12-14 foot span, can't remember) chainsawed the tops flat, laid 2x6 across them and then laid another 2 lines perpendicular to those. (basically where the tractor tires go) heavily coated the logs to help keep them from rotting, lumber on top is pressure treated. My tractor with loaded tires and backhoe on has to be well over 3,000lbs - probably close to 3,500lbs or more.
Key is the logs are almost directly under wheels so they take the weight not the 2x6's. There is no flex at all in the bridge to this day. I do inspect it because my choice of logs is crap! Lol But they are free on the property and when the day comes that I suspect they are no longer going to hold up I'll replace them.
I do have one trailer that I've occasionally taken across loaded that has a wider axle then the tractor and the wheels aren't directly over the logs, even that with easily 2,000lbs in it the 2x6's held up. They did flex, I wasn't keen on doing that... I've since got another trailer that matches the width of the tractor so no more worries...
Long-winded answer - but basically if your tractor will be driving directly over the your 6x12's or even partially over them then I'd feel good about 2x6's - especially if you do as I did and lay a couple rows of 2x6's in the direction of travel where the tires will be. If you're going with thicker than 2x material then I'd be less inclined to worry about a second layer like I did. Otherwise having that second perpendicular layer helps spread the load nicely.

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[kevininor]

Can you add an additional 6x12 in between the other 2? This would add a lot of stiffnesss and capacity.

Thanks kinda what I'm thinking will ultimately solve my questions.

 

[kevininor]

The OP asked for information/opinion.....now he (and you) don't like the result?
I assume this site to be fact based.
In my world, warm and fuzzys are for politicians.

For clarity, I am the OP and I'm grateful all the information and opinions provided...

 

[kevininor]

Thank you all for the responses. Lots of good information to ponder. I am currently driving over the existing bridge with my little JD X330. Including me, that weighs about 800 lbs. I am able to aim for one of the stringers minimizing impact and the 2x6s are flexing a bit.

I'm planning to add a Johnny bucket to it thus am likely to see the total weight go up to around 1200 lbs when fully loaded.

Based on my research and the feedback here, I think I'm going to pursue adding a third timber to reduce the gap between them down to about 30". That, coupled with new 2x6s should get me the 2000 lbs I'm looking for. While I've got the deck off, I'll inspect the existing timbers and make a call.

 

[Grumpycat]

Can you add an additional 6x12 in between the other 2? This would add a lot of stiffnesss and capacity.

Won't help unless the existing two are spaced a good bit wider than the track of the vehicles crossing. If two are spaced approximately the same distance apart as the wheels then a center beam won’t carry anything.

 

[kevininor]

The width of my current tractor is about 40 inches.