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Discussion Starter #1 (Edited)
So my culvert/dirt bridge over my creek has washed out 3 times this summer. We had 3 major floods, and each time the water completely covered the bridge, clogged the 2 18" culverts and then removed most of the dirt and one of the culverts this last time.

I'm finally going to build a real bridge, so as to not wash away. My family owns a metal shop, so I'm getting 3 I-beams for the span from them, 16' long each. They should according to my calculations handle 8000 lbs of single point weight in the middle of the span, with acceptable deflection (< 0.75"). I have a 2038r which is 2500#, but by the time you add ballast, loader, me and max loader load is ~6500#, and I wanted some extra margin above that. Extra capacity would be needed if I get stuck on the far side again and need to call my brother to pull me out with his 4066r or H1 Hummer. I plan to have each of the 3 beams get a ~2-3' long pipe welded to each end. Then I'll dig a hole for each in the bank and pour concrete to make sure it doesn't move. Then I was thinking of using pressure treated lumber for decking boards that I attach to the beams with U-bolts. Any advice on what size boards I should use for the decking? I was thinking of making it 8' wide as much lumber comes in 8' or 16' increments, but at 8' that would be the exact width of the H1 and pretty tight for the 4066r (wide tire setting, and 4" spacers) so maybe I need to do 10'. But that would also mean that the tires on most of these wouldn't be right above the beams anymore, so I'd need to make sure the decking could handle that weight. We know metal & the math to make sure we get it strong enough, but I'm far less sure on the wood side. Also is there any type of wood I should favor over another? While it does flood potently a handful of times per year, the majority of the time it will be 3-4' above the water level. The actual creek width is 10-11' where I would be spanning it.
 

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Someone in Richmond must sell this type thing,,,

Box Culvert - Permatile Concrete Products Company

Drop the tractor or H1 into the creek, the box culvert will look cheap,,,

They just installed the Permatile culvert under a local road,, a VERY nice product,,, :good2:
 

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From your post, I cant see how you intend to lay out the bridge itself.
Materials and loads are fairly simple to calculate, but what you absolutely must take into account, and Ive learned this from experience, having several small bridges wash completely away, is the stress the water puts on it.
The best thing you can do with regard to this is to make sure the beams dont hang down into the water. What I mean, and its hard to describe without pictures, is that you want the lowest portion of the beam to be above the highest level of the land. This means your bridge will have an approach and departure angle.
We tried for a VERY long time at my grandfathers to avoid this. It meant we replaced bridge decks several times, and even tried abandoning the old concrete piers that were poured and making new ones in a different spot. It didnt work.
In the end, the small stream had such power when flooded, even without breaching the bank, that it would erode the earth behind the concrete.

The final solution included very little concrete. Only enough for three 3' deep holes on each side to anchor the main cross beams. The creek flooded several times in the 6-7 years before the property was sold, and never weakened in the least, unlike previous attempts.
The reason was the deck was elevated so that when the water breached the bank, only then would it be able to push on the bridge, and because the water had somewhere else to go, without increasing pressure, it never damaged the bridge.

I hate to add another dimension (figuratively and literally) to your plans, but Id certainly think about it, since you dont want to be doing this again anytime soon.
 

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If your bank width is 10' to 11', it becomes obvious that the 2 18" culverts were WAY undersized, which is why they can't hold up. I would speak with a local engineering firm to have them do a hydrological survey to determine the proper culvert size to be able to pass the expected water flow. It may be easier than trying to design and build a bridge that may be too narrow to be practical. You could end up with 3 - 36" culverts, but that would be an engineered design, with a design storm of 25 to 50 years.

I also would raise the road elevation in the area of the culvert so that any overtopping doesn't occur in the area of the culverts.

Dave
 

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You're local NRCS office can tell you what size pipe is needed. Whatever size they say I'd use and then use rip-rap on the above and below stream sides of the structure. Including the creek floor 10- 20 feet down stream.

The traffic area of the top use a heavy clay gravel. Several I've down before I rip-rap the entire structure and in the traffic portion I fill the gaps with crushed stone.

I'd use #50 rip-rap and have it laid with a track hoe around 1.5 to 2 feet thick. You are only covering the structure so it won't take a lot to cover it. A track hoe can lay that rock tight so it can be driven over even if the top material for smoothness is moved from scour.

The overtopping will be short duration for the most part but it's designed to be overtopped.

Bridges will last awhile but will eventually need heavy maintenance.
 

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Discussion Starter #6
From your post, I cant see how you intend to lay out the bridge itself.
Materials and loads are fairly simple to calculate, but what you absolutely must take into account, and Ive learned this from experience, having several small bridges wash completely away, is the stress the water puts on it.
The best thing you can do with regard to this is to make sure the beams dont hang down into the water. What I mean, and its hard to describe without pictures, is that you want the lowest portion of the beam to be above the highest level of the land. This means your bridge will have an approach and departure angle.
We tried for a VERY long time at my grandfathers to avoid this. It meant we replaced bridge decks several times, and even tried abandoning the old concrete piers that were poured and making new ones in a different spot. It didnt work.
In the end, the small stream had such power when flooded, even without breaching the bank, that it would erode the earth behind the concrete.

The final solution included very little concrete. Only enough for three 3' deep holes on each side to anchor the main cross beams. The creek flooded several times in the 6-7 years before the property was sold, and never weakened in the least, unlike previous attempts.
The reason was the deck was elevated so that when the water breached the bank, only then would it be able to push on the bridge, and because the water had somewhere else to go, without increasing pressure, it never damaged the bridge.

I hate to add another dimension (figuratively and literally) to your plans, but Id certainly think about it, since you dont want to be doing this again anytime soon.
My plan is to cut the beams on a 45 angle on each end so I can lay the first/last plank on an angle to make a brief on/off ramp. I was going to lay the 3 beams on top of the existing bank and pour a 2-3’ deep hole of concrete for each beam end (with metal running perpendicular to them beam into the concrete) to keep it from washing away. What I was picturing sounds pretty similar to what you were describing.




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Discussion Starter #7
If your bank width is 10' to 11', it becomes obvious that the 2 18" culverts were WAY undersized, which is why they can't hold up. I would speak with a local engineering firm to have them do a hydrological survey to determine the proper culvert size to be able to pass the expected water flow. It may be easier than trying to design and build a bridge that may be too narrow to be practical. You could end up with 3 - 36" culverts, but that would be an engineered design, with a design storm of 25 to 50 years.

I also would raise the road elevation in the area of the culvert so that any overtopping doesn't occur in the area of the culverts.

Dave
The bank width is 10-11’ at the top, but only around 5’ at normal water level. I don’t have a backhoe so digging out that wide of area by hand isn’t realistic to put significantly larger culverts.

After observing the flooding this year I would have to raise the road bed by probably 4’ over a 100-150’ long span to get it above the water at the peak flood level I’ve observed. and then I’d have the entire length of the road that would need culverts all along it to not wash out.


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So my culvert/dirt bridge over my creek has washed out 3 times this summer. We had 3 major floods, and each time the water completely covered the bridge, clogged the 2 18" culverts and then removed most of the dirt and one of the culverts this last time.

I'm finally going to build a real bridge, so as to not wash away. My family owns a metal shop, so I'm getting 3 I-beams for the span from them, 16' long each. They should according to my calculations handle 8000 lbs of single point weight in the middle of the span, with acceptable deflection (< 0.75"). I have a 2038r which is 2500#, but by the time you add ballast, loader, me and max loader load is ~6500#, and I wanted some extra margin above that. Extra capacity would be needed if I get stuck on the far side again and need to call my brother to pull me out with his 4066r or H1 Hummer. I plan to have each of the 3 beams get a ~2-3' long pipe welded to each end. Then I'll dig a hole for each in the bank and pour concrete to make sure it doesn't move. Then I was thinking of using pressure treated lumber for decking boards that I attach to the beams with U-bolts. Any advice on what size boards I should use for the decking? I was thinking of making it 8' wide as much lumber comes in 8' or 16' increments, but at 8' that would be the exact width of the H1 and pretty tight for the 4066r (wide tire setting, and 4" spacers) so maybe I need to do 10'. But that would also mean that the tires on most of these wouldn't be right above the beams anymore, so I'd need to make sure the decking could handle that weight. We know metal & the math to make sure we get it strong enough, but I'm far less sure on the wood side. Also is there any type of wood I should favor over another? While it does flood potently a handful of times per year, the majority of the time it will be 3-4' above the water level. The actual creek width is 10-11' where I would be spanning it.
Sounds good. 4x6 PT should be good. I think it's pretty much what they use on small roadway wooden crossings.
 

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I would lay out the iron so that it rests under your tires. No reason you can't have the wood overhand the outside beams, but your point loads are going to be where your tires are. Then you could weld on some 1/4" steel supports if you felt like it was necessary to support the wood planks at the ends.
 

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Discussion Starter #10
I would lay out the iron so that it rests under your tires. No reason you can't have the wood overhand the outside beams, but your point loads are going to be where your tires are. Then you could weld on some 1/4" steel supports if you felt like it was necessary to support the wood planks at the ends.
Yeah this is the plan. But I’m going to align the beams with my brother’s heavier 4066r’s tires. My 2038r will be fine a foot or two inside them. The beams arrived, just waiting for my brother’s company to cut them and weld the vertical parts that get secured in concrete. He is taking forever but you can’t rush free.


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Box culvert supplier

Someone in Richmond must sell this type thing,,,

Box Culvert - Permatile Concrete Products Company

Drop the tractor or H1 into the creek, the box culvert will look cheap,,,

They just installed the Permatile culvert under a local road,, a VERY nice product,,, :good2:
Concrete Pipe Products in Ashland, Va has that type product. There may be other suppliers in the Richmond area as well but this one isn't far from you.

Concrete Pipe & Precast: Trench Drains

Treefarmer
 

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Well...

I'll get to my take on the wood question part of your post, but you gotta put up with my bridge story first. Glad to know you've got the steel part down, and it seems to me you're on the right track - See this... https://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=nrcseprd1337676&ext=pdf
I found good, practicable information in that guide as I considered my own situation – you may find useful info in it that you can apply to your circumstance and situation.

I recently moved up from a vintage garden tractor to a 1025R. I used a 36" tiller on the garden tractor, and occasionally pulled a small utility trailer filled with broken concrete, so those were the heaviest loads (with me on the seat) that ran across my bridge, which was built with that tractor in mind. I suspect that my largest load on the bridge was about 1200lbs total. The 1025R is a whole ‘nother matter, because by my WAG I could see the far side of 2.5 times that load on the bridge, and I figured it's not stout enough. A structural engineer, of course, agreed when I had him look at potential loads. To compound the issue, I’m not really certain what I have with the current bridge… more on that below.

What I found in forum conversations didn't provide much in the way of practical, solid experience or advice to the folks posing such questions, and they often quickly morphed into comments I’ll summarize as “it's gonna take years and cost 10's of thousands of dollars”. I already have a bridge I was tempted (ok, after a beer, but even then not really) to run my 1025R over! I just wanna be safe doing it, and want some idea of what I need to do it reasonably safely. The pdf above gave me the best, grounded info to be found on the 'net, and based on reading it I have both a temporary solution I've been using already, and a better plan for next spring.

If you're still reading, this is what I have: 33' clear span, 60" wide using two 12” deep 35' long beams that were salvaged from an old trailer frame. The beams are ~38" on center, decked with 2x8 redwood (which needs replacement). Ends are set on large salvaged, treated bridge timbers for footings which are roughly 12x14x5', and there's no concrete anywhere. I'm not thrilled with the current bracing between the beams, but it is braced with steel. The old tractor has gone back and forth across it hundreds of times over the years. My gut (and the engineer, too) told me that there'd be enough deflection with the 1025R that I'd not want to cross without some improvement. Finally, yeah, it's been in place for 30+ years (I can't really recall except to within +/- 2 years) and, no, I don't know any more about the beams. To add to the story, one of the beams has a gusset and appears, maybe, to have been spliced! I know who built it, a farmer who knew it’s intended use, and it was built with a mind toward practical and reasonable use.

The temporary solution to getting the new tractor across has been to set at the center of the span a single jack post like this: https://www.homedepot.com/p/Tiger-Brand-Super-S-7-ft-9-in-Jack-Post-J-S-93/100540359?MERCH=REC-_-PIPHorizontal2_rr-_-100041510-_-100540359-_-N
I’ve had the 1025R with a moderate load in the FEL and either the ballast box or 260B backhoe across this ‘temporary’ solutions many times already, and while I know there’s some deflection, I can’t detect it while I’m on the tractor… feels very stable. The present unsupported span from that jackstand to the end supports is about 16 ½ feet. It’s useful, it feels stable and safe for my tractor, and I’ll be happier still after I get the ‘permanent’ solution in place. It’s hard to see the jack post, but it’s there and is within an inch or two of center, both lateral and span.

Bridge Photo.jpg

The permanent solution is going to be to re-construct the bridge by adding two W12-19 beams to the bridge and improve the cross bracing. I'm going to put the new beams under the 1025R’s inner tread centers and move/re-use the current beams ~10-12 inches outboard (whatever gives my welding buddy room to work), and re-deck with new 2x8 redwood or cedar (rot-resistant, and I prefer those to avoid the possibility of leaching from treated lumber into the stream). I may reset the current timber 'footing' on a concrete footing, but may not... still pondering that part of the plan, with a mind toward how authority figures would look at excavation and placement of such a footing. I figure that I’ll be able to get it done for about $1800; I’ve already accepted the idea that, by the time I’m done, it’ll take twice that amount.

My words on the wood question, finally: Because in my case the beams are generally under the tread of the tractor, I don’t worry so much about the thickness of the decking because the load is going to be for all practical purposes straight down to the beams. It works that way now, and I think a thicker 3 or 4” decking timber adds to the static bridge load where I’d rather use that for the load of the tractor. With different spacing, I’d think differently, and if you're gonna put a hummer or bigger tractor over it, thicker decking is probably appropriate. At 10 feet wide, will somebody, someday try to put a cement truck or school bus over it?

I’ve read a huge number of forum conversations about bridges like this: Mine is for foot use and for my 1205R, only. It’s on private property, and it’s neither wide enough or nor approachable for use by fire trucks, cement trucks, school busses or even the neighbor kids’ Ford Ranger. If the next owner wants to try when I’m dead, that’s on them because it’ll be sold just like the house: Without warranty of any sort.

T
 

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Another alternative

If you haven't gotten started on your bridge, you might look at this: Metal Culvert - farm garden - by owner - sale

A 48" culvert will handle a lot more water than 2 18" culverts. The cross sectional area of the 48 culvert is roughly 1800 square inches and the two 18s combined are just over 500 sq inches. Add in less turbulence, less chance of debris getting stuck and the larger culvert is a lot more efficient at getting water from one side to the other.

Treefarmer
 

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Discussion Starter #14
If you haven't gotten started on your bridge, you might look at this: Metal Culvert - farm garden - by owner - sale

A 48" culvert will handle a lot more water than 2 18" culverts. The cross sectional area of the 48 culvert is roughly 1800 square inches and the two 18s combined are just over 500 sq inches. Add in less turbulence, less chance of debris getting stuck and the larger culvert is a lot more efficient at getting water from one side to the other.

Treefarmer
That would have the top of the culvert at or above ground level so I wouldn’t have room for dirt above it. Even if I just mounded dirt above it I now know that dirt will wash away when the water rises above the culvert which it will do.

I’ve ordered all the materials, so...


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