Bridge Ideas for multiple creek crossings

[Gordon Gould]

What is the weight and how does it get moved?

In my case I plan on two 8' panels to span 6'. Each panel will have 6 - 6X6 and 7 - 2X4 to make up about 4' wide. It will be eastern hemlock or southern yellow pine and weigh less than 1000 lbs - probably around 800 with green lumber less with dry. I will place it like this.

gg

 

[WinterDeere]

I was on a farm that bridged irrigation ditches with concrete slabs about 8 feet square, 4-6 inches thick. No idea what was inside the slab. Ditches were 4-5 feet wide.

Bruce

Most likely, a lot of steel. Either rebar grid in 3 dimensions, or even I-beams. Concrete is impressively weak, in this configuration, but it does a good job at protecting the steel and providing a drivable surface.

 

[2manyrocks]

Thanks for all of the quick replies and good advice. rather than quote everyone I will do my best to answer the questions all at once.


The choice of materials was mostly based on what I have on hand right now, I have an endless supply of free 2-7/8 pipe, I can get oak boards for the decking done for just the cost of having them cut up as we loose oak trees every year.

4 of the 5 crossings are just 18" deep, 1 is about 3' deep. I would prefer a bridge to a low water rock crossing so I can cross at anytime.

The issue I have with culverts is we do a lot of controlled burns here so that would make me install galvanized culverts, also with all of these crossings being in timber areas pine straw, oak leaves and branches will clog the culverts like they do at all of the road crossings. after every hard rain I have to clean all of them out and with a bridge most of that will flow underneath.

at another property we have we have several bridges that are 4 telephone poles, two per side and then decked with shaker screen from a rock quarry and they have been holding up for 20+ years, however this is just for UTV traffic not truck or tractor traffic.

most of these crossings will look very similar to the youtube video posted by bmaverick except lots of trees all around.

I will try and get a few pictures this weekend of what I am looking at.

the stream is not very fast even during a hard rain, there is about 10' of elevation change over the course of 500 yds straight line distance but the creek winds the whole way so it moves slowly.

One of the issues with bridge construction is building abutments with footers that won't wash out. I wonder whether some of the new bridges being built on soil in youtube videos will still be there after a few good rains.

 

[2manyrocks]

In my case I plan on two 8' panels to span 6'. Each panel will have 6 - 6X6 and 7 - 2X4 to make up about 4' wide. It will be eastern hemlock or southern yellow pine and weigh less than 1000 lbs - probably around 800 with green lumber less with dry. I will place it like this.

View attachment 1938174


View attachment 1938175

gg

In this picture, you've got that V plate under the grill guard to hold the log in place, but how do you plan to anchor a 4' wide panel?

 

[Gordon Gould]

In this picture, you've got that V plate under the grill guard to hold the log in place, but how do you plan to anchor a 4' wide panel?

You mean on the abutment ??

 

[2manyrocks]

Sorry, no, I mean how will you anchor the 4' wide panel when you lift it with your FEL so it can't swing back into your radiator, etc?

 

[Gordon Gould]

In this picture, you've got that V plate under the grill guard to hold the log in place, but how do you plan to anchor a 4' wide panel?

Id you mean anchor the panel to the tractor ? Maybe the V will work. If not I'll take it off and there are 2 shackle lugs right there that I can use. I'm sure I can make something work.

gg

 

[2manyrocks]

Side to side movement of the panel during transport could rip a tire sidewall.

 

[Gordon Gould]

Yes sir it could.

gg

 

[Renze]

Beam stiffness changes by the cube of the change. So a beam twice as tall is 8 times stiffer.
Eric

A factor two, squared (2x2) was four, last time i calculated a bridge

52°28'38.8"N 6°12'29.8"E

maps.app.goo.gl

Switch to satellite view to see the bridge

I calculated this home made bridge for my mate, spanning 12 meters between the abutments.

The waterway council had a say in it, and because i am not a civil engineer i calculated a bit rich for the building permit.

Found the minimum average foundation to soil contact pressure for our sool type, didnt know about the rules for pier washout so we put the piers at the same level as the canal bottom, just to make washout precautions unnecessary.

We ordered some prefab inverted T shape retaining walls, i converted the manufacturers rated side load to a bending moment, converted that to a maximum vertical load. It surpassed actual loads by a factor of 7 to 10, both in surface load as well as bend moment where the T joins.

For deck i calculated 4 beams IPE 500 were enough to carry 60 ton with a safety margin of two. The seller only wanted to sell all 9 at once so we ended up welding flat strips between all 9 of them, to create a 4 meter wide bridge with a fail point of 300 ton.

Dressed up with links to data used, both generic foundation load as well as retaining wall element manufacturers specs, they just stamped it for approval and gave us the green light

The water council payed him a temporary log bridge beside the old bridge, which took a contractor longer to build than it took us to build the permanent bridge in the location of the old bridge. I bet ours was a fraction of the cost too.
I assume at the waterway councils office, a civil engineer had a big grin on his face while shaking his head when he stamped the approval sign on the plans

The old bridge was built in the 60s when gramps and uncle bought the land across the canal and wasnt used with the slurry tank for the last two years because 50 years took its toll on the tiny I beams, but we expect this bridge has so much reserve that it will take 150 years of decay before you must stop using it with 60 ton combinations.

Cost: 6000 euro for the used beams, 500 euro a piece for the retaining wall elements used as abutments, maybe 500 euro for the flat strips, and a bunch of welding wire.

Another mate worked as a crane operator and hoisted the stuff in place on a saturday, and the local contractor came with a 15 ton digger to dig the abutments.

We chose to dig in the wet, so the hole wouldnt collapse from water seeping in (theres no chance to pump the dug pit dry with infiltration pipes, so close to the canal, without damming the entire canal)

Had it been done by a civil contractor, it would have cost 120.000 euro and had a quarter of the technical reserve.

 

[pmsmechanic]

Around here people use 3 ton or school bus frames for pivot bridges. Two of them set side by side would be adequate for vehicle use if covered with 3 by xx wood that is bolted down. I would make sure the frames are centered with the vehicle tracks.

I would also just make one bridge that is suitable for vehicles/tractors and the others can be lighter for quad/pedestrian use only.

A concrete footing poured either in place or transported during the dry season would make sure the bridges lasted a long time.

Just my thoughts.

 

[WinterDeere]

There have been some great ideas posted here, for 20 and 40 foot spans. But I think everyone is forgetting that the OP's crossings are just 3 to 7 feet. I could've had the culvert pipes delivered, installed and buried, in half the time this thread has played out!

Go concrete, if money is no object. Otherwise, get yourself some corrugated culvert pipes of diameter equal to the crossing width, excavate, drop them in, pour some gravel to top of pipe to lock them in, and then top all that with dirt and grass to keep the gravel in place. If you really want to go the extra mile, stack bagged concrete around each end, as headwalls, they actually look like stacked rock after the bags deteriorate and wash away. You could have several done in one day, esp. if you know anyone handy with a mini-excavator.

 

[Gordon Gould]

I replaced a failed logging bridge at the outlet of a swamp with a culvert. It was doable but not that easy.

Pull out old bridge and dig a culvert trough in the muck.

Set Culvert

Cover and cushion with 3/4" gravel.

Bring gravel one bucket at a time 1/4 mile down skidder road from closest landing.

Beef up culvert covering and trail with 3-1/2" road base.

gg

 

[etpm]

A factor two, squared (2x2) was four, last time i calculated a bridge

I said cubed, not squared, so 2x2x2, which is 8. It is not intuitive. Twice as tall is 8 times stiffer. Not twice as stiff.
Eric

 

[Renze]

I said cubed, not squared, so 2x2x2, which is 8. It is not intuitive. Twice as tall is 8 times stiffer. Not twice as stiff.
Eric

Then you said it wrong: lets do the math:

Bend resistance is 1/12 times breadth times width cubed, divided by the exterior fiber distance. In case of square beams, exterior fiber distance is half height.

2 by 4 is 1/12 x2x4x4x4 divided by two is 5.33
2 by 8 is 1/12 x2x8x8x8 divided by four is 21.3

21.33 divided by 5.33 is four, not eight.

You are confusing the moment of inertia (cubed) with the bend resistance (squared because bend resistance is moment of inertia divided by the most exterior fiber distance.

 

[BackRoad]

Hold on while I get a bag of popcorn to watch this drama...

 

[Sportsman762]

4 of the 5 crossings are just 18" deep, 1 is about 3' deep. I would prefer a bridge to a low water rock crossing so I can cross at anytime. Also with all of these crossings being in timber areas pine straw, oak leaves and branches will clog the culverts like they do at all of the road crossings

With a bridge this low it will be impossible to clean under it. Atleast with an 18' culvert you can fabricate something to drag through it. an 18" clearance under the bridge is a recipe for trouble. Every example shown of bridges posted so far has 3 feet or more clearance to bottom of stream.

I replaced a failed logging bridge at the outlet of a swamp with a culvert. It was doable but not that easy.

Pull out old bridge and dig a culvert trough in the muck.
View attachment 1944098

@Gordon Gould photo shows what happens with low clearance bridges and their lack of viability.

Putting a trash guard or beaver cone will reduce some of the clogging issues, as does digging a settling hole in front of the culvert inlet. I have a 8" culvert 100' long that gets full of leaves and sticks and putting a settling hole in front mostly cured the clogging issue.

I can get oak boards for the decking done for just the cost of having them cut up as we loose oak trees every year.

The issue I have with culverts is we do a lot of controlled burns here so that would make me install galvanized culverts,

If plastic pipe is a problem with controlled burns how is wood decking going to work? On the levees I did we would bury make sure the pipe was completely covered on the top with dirt to reduce the embers landing on them. Then before the controlled burn we would disc around them so the fire could not reach them. A wood decked bridge would be very susceptible to catching on fire during or shortly after a controlled burn even with a firebreak around it as embers would land between the decking and beams potentially starting a fire long after the burn was done.

I know it seems as if I am pushing a culvert and ignoring the bridge option but I do not see how it is viable for this situation. @WinterDeere sums it up well.

There have been some great ideas posted here, for 20 and 40 foot spans. But I think everyone is forgetting that the OP's crossings are just 3 to 7 feet. I could've had the culvert pipes delivered, installed and buried, in half the time this thread has played out!

@Renze That sounds like an impressive bridge. Any photos of it?

 

[RayIN]

Bridges want to fail. It's just a matter of when that happens. The more wood that you use in your bridge, the sooner something will fail. If you are dead set on building a bridge, the next question you need to ask is how long do you plan on using it? Are you young and expect to use this bridge 50 years from now? Are you retired with a decade or so of time left that you'll be needing it?

From what you have said in your original post, it does not sound like you have a lot of experience in framing. Your choices of materials listed to build the bridge are not what I would use. Even more important then what you use to build the bridge is what you use to support it. That needs to be the first question.

Culverts are simple, affordable, and if sized big enough, will last for a century. If they fail, it's easy enough to fix it and use it again.

Even easier is to just dump a lot of large rock in the bottom of the crossing.

A long time ago a man I knew had one large creek to cross when building his house. He found scrap semi-oil tanker trailer. Had it towed to his place, removed the tank from the frame and cut-off the ends, then had a man that build ponds/lakes prepare the creek-site and put the tank in place. Then he flattened the tank to fit with the track-hoe bucket.
Once the back-fill was completed, it became part of the crushed stone driveway.

 

[Renze]

.@Renze That sounds like an impressive bridge. Any photos of it?

Sorry, was at my mate this afternoon in the shop, but didnt think of making a photo.

 

[2manyrocks]

Sorry, was at my mate this afternoon in the shop, but didnt think of making a photo.

I would also like to see a photo of your work. Satellite view was hard to see the details.