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+-- Thread: A bridge for my tractor - will it support it? (/showthread.php?tid=7146122)
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A bridge for my tractor - will it support it? - comfun1 - 11-18-2015
I have a small stream in my back yard that I need to cross mostly for mowing with my RZT 50 but occasionally I need to get my Kubota B7100 across. The Kubota has a front end loader and the heaviest rear attachment would be my tiller. I'm guessing the total weight would be around 2,000 lbs. My bridge will be six feet wide and twelve feet across. To span this twelve feet I am thinking of treated 2x10's spaced 12" on center with 2x6 decking. Does this sound adequate to support the tractor and implements? Thanks
Re: A bridge for my tractor - will it support it? - Phil Thien - 11-18-2015
I'm not an engineer but I'm going to say "no."
Your load from the tractor is not evenly distributed, there is more load concentrated over the wheels. Some load will transfer to the interior joists but the outside joists neat the wheels are going to take the brunt of it.
I'm guessing some engineer type will be along shortly but I think you're going to need something more robust.
Re: A bridge for my tractor - will it support it? - jteneyck - 11-18-2015
This calculator says that should be OK. Your live load is only 28 psf and your design should handle 50 with no problem.
John
Re: A bridge for my tractor - will it support it? - brianwelch - 11-18-2015
Without running calculations, I would definitely double (at least) up joists at the wheelpaths and make sure you use a good bridging method to tie the assembly together... You might want to allow for a full loader bucket in your weight calculations, along with the largest combination of driver/passenger(s)...
Re: A bridge for my tractor - will it support it? - Estrogen Hostage - 11-18-2015
No, this is a very bad idea.
Were it me, I would use an old semi trailer set on concrete piers with railroad ties on top for the decking.
Re: A bridge for my tractor - will it support it? - comfun1 - 11-18-2015
brianwelch said:
Without running calculations, I would definitely double (at least) up joists at the wheelpaths and make sure you use a good bridging method to tie the assembly together... You might want to allow for a full loader bucket in your weight calculations, along with the largest combination of driver/passenger(s)...
Good idea, doubling joists under wheels and I never thought about the weight of the load in the bucket.
Re: A bridge for my tractor - will it support it? - meackerman - 11-18-2015
don't let the EPA know you're building a bridge over a stream.
And if you're in a stupid state like Cali, don't let any government agency local, state or federal know.
Re: A bridge for my tractor - will it support it? - CLETUS - 11-18-2015
We used telephone poles under the wheel path and decked it with 2" WO from the Amish saw mill. The tractor is 2,500lbs base weight.
The load calculations were me driving the tractor across the bridge.
Re: A bridge for my tractor - will it support it? - TDKPE - 11-18-2015
I don't design in wood, but if it were me, and I were doing my own design, I'd assume the full loaded weight at the center of the span, in two locations, one for each wheel. Essentially two point loads. Plus half the dead load of the bridge structure, of course. For bending stress on the beams, that is.
For the foundation loads, assume the same two point loads directly on each bearing point, plus the dead load of half the bridge structure, of course.
That's overdesigned, but it's a) out in the weather, and b) not likely to be expensive anyway, and if you have to double or triple up the beams under the wheel path, that's just another couple of boards.
Assuming PT framing lumber is even acceptable for this. As I said, I don't design in wood, and really don't have much feel for how much load you can put on framing lumber of a give size and span. But that's what span tables are for, I guess. But that will yield a very conservative design, as you're not taking into account the spread of the axles, which can greatly reduce the actual bending moments on the beams on such a short span bridge.
Re: A bridge for my tractor - will it support it? - Splinter Puller - 11-18-2015
all you need are two planks.
https://www.youtube.com/watch?v=HBw7-XQHdAA