How strong is my wooden bridge?

[daugen]

Directly through the mid section of my property is a large ditch used for water drainage of course, which heads off down somewhat endlessly in one direction along a farmer's field. Over that ditch is a small wooden bridge used originally for the prior owner's kids to ride their horses over to get to the neighboring fields. So not built for machinery at all I believe.

I of course want to get my Kubota across this thing, say about 5000 pounds worth, since on the other side are twelve acres with a pond hidden in the middle I want to clear. So I need to get my tractor over that ditch.
And the obvious answer to my thread question is not very strong after I saw the flash pics of the rotting beam
underneath. Yikes. Decent new top put on, covering lots of rot underneath. Lovely. Fine for the UTV but obviously not fine for a tractor.

So let's assume the rotting pieces are fixed...then what. How strong is this construction?
I was thinking, like an Army Engineer Corps guy, how to strengthen this bridge temporarily.
There isn't any support underneath so this is a single span.
I was thinking of getting oversized lumber, 5/4?, not sure of term, and laying boards down on top of the existing bridge, but extending at least a foot further out. Then what, a couple of house jacks underneath supporting a lateral six by six on top and the same underneath in the ditch bottom? Otherwise it's going to bow in the middle with a mighty crack I believe...

I'd appreciate any and all comments about how to fix this thing properly; (yeah, get it off the silly tree...)
and how strong a wooden bridge has to be to take a three ton tractor over. I'm thinking of the wood decking on a trailer and that sure doesn't seem very strong, but of course it's all about support underneath. Of which I seem to have none...
I'm really not interested in sinking concrete piers at the moment, nor building a new bridge.

Can I repair it and then overlay or is that just a waste of money, which should be put towards rebuilding it to support serious weight?

 

[Scrambler82]

From a novice view point... based on the condition of the beams, the wetness of the beams, the growth of the cut down trees and the one growing into the bridge, also the end supports and the weight to be transported, I would replace it.

If you added supports in the middle, it might work for a while but to me you are on a time bomb.

IMHO, that's all folks.

 

[k0ua]

Drew, did you carry a screwdriver under with you and jamb it into the supports at several places to test for durability of the support wood? That is what I would do. And just how big are those beams?

 

[rswyan]

The beams (obviously) need to be replaced ... don't know what the spacing is on them now, but ideally when you put the new ones, they will match the track (width) of your tire/wheel spacing.

Even more ideal might be to add two more (for a total of four) ... at the outside edges.

 

[murphy1244]

Drew, If I had your size machine I wouldn't even use that bridge. Just go around it.:thumbsup:

 

[daugen]

ok, I can't go around; ditches on all sides; think a moat around your castle and you have to get across...
use of screwdriver an excellent idea; will go poke around tomorrow but it looked pretty visually nasty.
And I sure looked up and down that creek bed for things that slither. Nice and dry at the moment...

 

[daugen]

The beams (obviously) need to be replaced ... don't know what the spacing is on them now, but ideally when you put the new ones, they will match the track (width) of your tire/wheel spacing.

Even more ideal might be to add two more (for a total of four) ... at the outside edges.

truly the more the merrier...I like the idea of spacing where the tire tracks are, thanks

 

[Scrambler82]

The beams (obviously) need to be replaced ... don't know what the spacing is on them now, but ideally when you put the new ones, they will match the track (width) of your tire/wheel spacing.

Even more ideal might be to add two more (for a total of four) ... at the outside edges.

Great idea but it leads in with the idea that the bridge needs to be replaced.

 

[bcp]

You can get some good bridge ideas from old wood railroad flatcar plans, like this one. This is about a 20 foot span, rated for 15 tons. Scale it down a bit on lumber size, use fewer lengthways beams, use one crossbeam and two truss rods, etc.



Treated 6x6 pole barn posts are usually readily available. I would use them for all my beams.

Bruce

 

[amaxwell]

I would replace with a new bridge. What is the total span of the bridge? Any chance of getting some steel beams at a reasonable price? Someone near me used an old flat railroad car as a bridge. For me the risk of my life or the risk my tractor would make me replace rather than take the risk.