How strong is my wooden bridge?

[farmer2009]

If you want an opinion on culverts I will give you mine. I have 2 culverts side by side, about 30 inches or so each. They are a pain in the "rear" to keep them from stopping up with sticks, then leaves, then mud, etc. and the water backs up , and I have seen it 12 foot deep, and runs over the road and erodes the other side. I had to buy a bunch more fill to go on the downhill side when I neglected to keep the sticks and muck cleaned out. It is at least a yearly job if not more depending on how much rain we have. I would much rather have one single larger culvert than the twin culverts, as the problem always start with a single stick across the inside edges where they are tangent and goes badly as the stick captures more sticks, then leaves etc. Not to mention the children s floating toys from the housing development upstream. I had no say in the culvert placing, they were there when I came, but I learned the hard way about the cleaning needed. For me it would be one large culvert.

I would go one step further. I would rather have a clear span bridge than even a single culvert much less a double culvert.

 

[k0ua]

I would go one step further. I would rather have a clear span bridge than even a single culvert much less a double culvert.

Yes, that would be ideal.

 

[daugen]

well said Jim, thank you. I think really I'm going to need to tend to it yearly no matter what
At least I won't have rolling rocks get in there, it's pretty sandy here but there are pockets of clay, and a mix of that is
the area underneath the bridge. Actually fairly clean down there thank goodness.
And no hissing sounds...

 

[k0ua]

well said Jim, thank you. I think really I'm going to need to tend to it yearly no matter what
At least I won't have rolling rocks get in there, it's pretty sandy here but there are pockets of clay, and a mix of that is
the area underneath the bridge. Actually fairly clean down there thank goodness.
And no hissing sounds...

Thats good, and keep in mind I live in the woods, so sticks and leaves are par for the course.. You may not have as much problem as your drainage might be better...

 

[daugen]

one thing that has to be attended to sooner vs later is the attachment to that tree. Did they not understand that trees grow upward?...it's pulled the railing up several inches and I sure wouldn't want to lean on it. Pretty rickety actually.

Is there such a thing as pre-made bridges? And I don't mean from Amazon...hah, I'm a Prime member, send me my bridge with free freight please...

 

[MossRoad]

If you want an opinion on culverts I will give you mine. I have 2 culverts side by side, about 30 inches or so each. They are a pain in the "rear" to keep them from stopping up with sticks, then leaves, then mud, etc. and the water backs up , and I have seen it 12 foot deep, and runs over the road and erodes the other side. I had to buy a bunch more fill to go on the downhill side when I neglected to keep the sticks and muck cleaned out. It is at least a yearly job if not more depending on how much rain we have.

I would much rather have one single larger culvert than the twin culverts, as the problem always start with a single stick across the inside edges where they are tangent and goes badly as the stick captures more sticks, then leaves etc. Not to mention the children s floating toys from the housing development upstream.

I had no say in the culvert placing, they were there when I came, but I learned the hard way about the cleaning needed. For me it would be one large culvert.

The pictures in the OPs post show a depth of maybe 4', not 12'. Its a very different situation than yours, which sounds like very undersized culverts for such a potentially high dam if they get plugged. Sounds scary.

 

[daugen]

Newbury, finally read through part of that bridge manual. Wow...even found a section on how to splice a beam
using a fish plate. I wonder how many folk know what a fish plate is. Might have a newer name...
that manual is enormous.

I think the ditch depth down stream of the bridge is five feet and upstream six feet. I'm guessing by the size of the trees it's been at least twenty years since this ditch was done professionally. Now it looks like an earth science lesson. Lot of erosion.

 

[MossRoad]

Refer to page 79 of this BLM document...
http://www.blm.gov/bmp/low volume engineering/J_Ch8_Culvert_Use_Installation_&_Sizing.pdf

 

[buckeyefarmer]

I've helped build wooden bridges on twp roads (many yrs ago). We used rough cut 2x12 oak as joists, double or triple under the main tire track area. Then nail oak 2x? across them for the decking. These were for small bridges the size of yours. We would drive nails with sledge hammers, sometimes drilling holes first for the nails. I know we took dump trucks across these wooden bridges. We also built them with steel I beams under the track area, then nail pt 2x4s on end across for decking, using metal clips that clip on the edge of the Ibeam, nailed to the wood.
I've got a small creek that I'd like to put a bridge across, but since I have a county road next to me, I just drive out on the road, cross their culvert across the creek, then enter my land again. Not worth it to build my own bridge. This little creek is always got running water, fed from "7 springs farm" on the other side of the road. my neighbor on the other side put a culvert across the creek, probably 24 or 30", and it has held up well with some heavy rains. Back on dad's farm we have a few farm roads thru creeks. Course we also have public roads thru creeks, here's one on a public twp road I went thru last year, water was almost a foot deep.

 

[k0ua]

The pictures in the OPs post show a depth of maybe 4', not 12'. Its a very different situation than yours, which sounds like very undersized culverts for such a potentially high dam if they get plugged. Sounds scary.

It can be. it has the potential to wash the whole road out if you let it go..It takes a big long sustained rain to get to that point, but if you don't clean them out at least once a year, it can happen.

 

[doxford jim]

There are gratings made that fit over the ends of culverts to reduce build up of rubbish and other material that floats down with water. Don't know what they cost or anything about them other than I have seen several on road culverts around my area.

 

[pmsmechanic]

one thing that has to be attended to sooner vs later is the attachment to that tree. Did they not understand that trees grow upward?...it's pulled the railing up several inches and I sure wouldn't want to lean on it. Pretty rickety actually.

Lets correct something here. Yes trees grow upwards but if you put a nail in a tree say 4' above the ground it will for the life of the tree stay at 4' above the ground. It's the tips of the branches that grow up not the trunk. The railing is crooked because the bridge has sagged. Not because the tree has grown upwards.

 

[MossRoad]

Lets correct something here. Yes trees grow upwards but if you put a nail in a tree say 4' above the ground it will for the life of the tree stay at 4' above the ground. It's the tips of the branches that grow up not the trunk. The railing is crooked because the bridge has sagged. Not because the tree has grown upwards.

You are correct, mostly. However, trees do shift and do go up a little bit over their life. They gain diameter, and the roots will lift the tree up some, too. That's why sidewalks get lifted by trees. Its only a few inches over the life of the tree, but its enough to cause problems.

 

[MossRoad]

There are gratings made that fit over the ends of culverts to reduce build up of rubbish and other material that floats down with water. Don't know what they cost or anything about them other than I have seen several on road culverts around my area.

They're called trash racks...
Refer to page 83 of this BLM document...

http://www.blm.gov/bmp/low%20volume%20engineering/J_Ch8_Culvert_Use_Installation_&_Sizing.pdf

 

[newbury]

Newbury, finally read through part of that bridge manual. Wow...even found a section on how to splice a beam
using a fish plate. I wonder how many folk know what a fish plate is. Might have a newer name...
that manual is enormous.

I think the ditch depth down stream of the bridge is five feet and upstream six feet. I'm guessing by the size of the trees it's been at least twenty years since this ditch was done professionally. Now it looks like an earth science lesson. Lot of erosion.

And unless you are in some rare microclimate area of North Carolina be aware of dramatic flooding occasionally.

 

[daugen]

Ok, I won't be so hasty about tree growth statements but they really do go up a little; I know from carving my initials in many, many trees in our woods growing up.
Buckeye, I read your post several times, very interesting. So you built your own beam by building up with oak planks. If I ever were to build a new bridge, a real bridge and not a culvert, I'd sure overbuild it. You know, a nice used M Kubota I want for banging around in the woods will sure weigh more than my L. Or a mini excavator. I would probably build it to carry seven to ten tons; a good safety margin. It's just a pond back there, never going to take a vehicle over the bridge.
He said now...

which begs the question, how strong are metal culvert pipes? How many feet of dirt would you need to pile on top to take, for example, a small bulldozer over, a nice D3. Like most guys, always wanted a bulldozer. Not very practical on my place but it sure would clear a trail nicely. So will a chainsaw and a pull chain. Now obviously culvert pipes are infinitely strong if built "properly", but if I dropped a five foot diameter pipe in a six foot ditch, with stone underneath, how much dirt has to go on top? I'm guessing that gravel goes on top first. Not an excavator guys, sorry if questions are stupid.

I'm really thinking that fixing this bridge up cosmetically and building something much stronger next to it or nearby makes the most sense. The bridge should last decades with just light use, say under a thousand pounds.

 

[zing]

The decking looks like it was replaced much more recently than the timbers, so why not just reuse what is good and redo it? All you would need is 4 solid timbers, plus some 2x12 to upgrade the strength for your tractor and some gravel.

Take the decking off and save it. Remove the timbers. Put some gravel down to solidify the beds and allow drainage from the new timbers. Lay across 4 new timbers, under the tires and at the outside edge. Put the decking back down, and then run 2x12's over the decking under where the tires of the tractor go to improve the strength. No more work or expense then a cluvert, when you take all of the silt removal and solidifying the banks to make the crossing fordable. A lot less upkeep over the years too, than a culvert.

If you want to be able to get that tractor safely across the stream you need to put some work in, why not choose the option that will be less maintenance over the long haul?

 

[GPintheMitten]

I agree with zing. You may be able to use some timbers from your property. You may benefit by upgrading the abutments.

I built a bridge. It's very rewarding.

I've installed a few culverts too but there's nothing romantic about laying tube in a ditch.

 

[farmer2009]

Drew, when replacing to timbers. Turn them 90* from their current position. This will make them a lot stronger.

 

[Egon]

( which begs the question, how strong are metal culvert pipes? How many feet of dirt would you need to pile on top to take, for example, a small bulldozer over, a nice D3. Like most guys, always wanted a bulldozer. Not very practical on my place but it sure would clear a trail nicely. So will a chainsaw and a pull chain. Now obviously culvert pipes are infinitely strong if built "properly", but if I dropped a five foot diameter pipe in a six foot ditch, with stone underneath, how much dirt has to go on top? I'm guessing that gravel goes on top first. Not an excavator guys, sorry if questions are stupid.

I'm really thinking that fixing this bridge up cosmetically and building something much stronger next to it or nearby makes the most sense. The bridge should last decades with just light use, say under a thousand pounds. )

Culverts come in different gauges thus different cover requirements.