How strong is my wooden bridge?

[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.