Need simple, durable bridge ideas

[jeepcj7]

I need a bridge to cross a dry creek that has water in it maybe 2 months out of the year. We had a lot of rain this year and due to the lay of the land I realized a culvert is not an option. Was looking for simple ideas to build a bridge to span a 10 ft gap so I can drive my tractor across in wet season. Was thinking of using an old flat trailer off a semi or something along those lines, any ideas?

 

[BTDT]

Maybe an old tandem axle trailer (like you would haul your tractor on) would work.

 

[RonMar]

How deep does the water get, how much waterflow can be expected? how much vertical distance is involved. If it is low and flat, perhaps a series of smaller culverts buried in gravel...

 

[svcguy]

One thought is to try and find a heavily damaged sea-can. Shipping containers are about $3000 for a good 40 ft unit up in British Columbia, but when heavily damaged, you can get them for about $500 - $1000. If you made arrangements to cut the sides and roof off and take only the deck, you might get it really cheap. (On a damaged unit, you are really in competition with the scrap guys at about .25 a pound). If you could find a 20 foot can and get just the deck, it would be very affordable.

Another possibility is to find a steel scrap yard or recycler and try to pick up a couple of nice, deep used I beams and deck them.

 

[GaryM]

One thought is to try and find a heavily damaged sea-can. Shipping containers are about $3000 for a good 40 ft unit up in British Columbia, but when heavily damaged, you can get them for about $500 - $1000. If you made arrangements to cut the sides and roof off and take only the deck, you might get it really cheap.

I'm not a structural engineer, but those containers are built so the sides and top add most of the rigidity to the unit. I think if you tried using only the deck it would fold like a cheap umbrella in the wind under any kind of a load.

Now if you cut down the sides to maybe 24-30 inches and added a horizintal steel plate about 8" wide welded to the cut down sides, you'd almost have a girder style bridge. I think it would take a much higher load in that configuration.

 

[tuolumne]

Do you have timber on your property? Cheap and simple sounds like two tree trunks dropped over the creek at the wheel spacing of your machine and deck them over. I assumed a 12' span with a 7000 lb concentrated load at the center. Using allowable loads for doug fir, you would need a pair of 12" diameter trees. I am sure you could create some sort of crushed stone area to bear the trees on and minimize rot. I agree with the above poster that a cut down container will have insufficient strength.

 

[kwolfe]

I am no engineer, however a 3 or 4 6x6x16 pieces of pressure treated lumber with 2x8 decking should easily support the weight of your tractor or a truck if you want to take it over as well.

 

[tuolumne]

I am no engineer, however a 3 or 4 6x6x16 pieces of pressure treated lumber with 2x8 decking should easily support the weight of your tractor or a truck if you want to take it over as well.

As a structural engineer, I would be nervous about such a setup...however, ignorance is bliss . Strictly by the numbers, 4 6x6 members would be insufficient for the load I mentioned. 7000 lbs is not an unreasonable axle load for a CUT with a bucket of gravel. Wood is very forgiving, and could perhaps perform OK for this transient loading, so this setup may work even though the calculations do not. Also, with the 6x6 option, there would be little load sharing to the inner members, and the members beneath the load would be severely overstressed. A safer solution would be to put the members in pairs below the wheels. Better yet, use something deeper.

 

[Knotbored]

The beams under modular homes (trailer houses set up permanently) look pretty sturdy, and several of those burn down every year. I would guess they are sold as scrap metal, perhaps an insurance investigator could give a hint where you could bid on one to get the beams.

Remember if you build an access over a stream then some day a curious tourist will sure as heck try to pull a 5th wheel over it and get stuck or swamped then blame you. I would invest as much in warning signs as in the bridge!

 

[SkunkWerX]

I really think we would need to know several things before suggesting anything. As Tuolumne has alluded to, we would need some of the following:

-Horizontal distance (across the creekbed)
-Vertical distance from assumed bridge surface to creek bed.
-Maximum load anticipated (Then apply at least a 2:1 Safety factor)
-Maximum width of load.
-Soil conditions at either side and in the creekbed for possible vertical supports.

Need more specifics.

 

[oldhippy]

Down here in the south old tractor trailer floor frames are used in quite a few places. The hardest part is getting the frame across the opening. If they are for something other than 4 wheelers then usually the ends are set on some sort of concrete piers. You can find these frames where they are scraping out trailers for the alum. from them. big dan

 

[kwolfe]

Another vary important questions is what kind of tractor are we talking about. 700lbs is a lot of tractor for most of the folks here. Some of the 30hp CUTs people have here only weight around 3000lbs with the FEL. Add weight for ballast and full bucket, and you may still only be talking about 5000lbs.

 

[MikesTractor]

A friend of mine had a small year round creek that he wanted to put a bridge across. From bank to bank he had to span 28 to 30 feet. He found some 12" x 24", approximately 1" thick and 64 feet long I-beams that the local public works had removed from a bridge that had been replaced. He bought 2 of these beams at scrap metal prices. I helped him move the beams. We cut them in half and hauled them on a semi-truck with a 40" flat bed. We were able to handle the beams with a large trackhoe.

You might check your local public works department and see if they have anything. He told me that he had less than $2500 in these beams. That price included charges for the semi truck and track hoe rental (Public Works loaded them for us after we got them cut).

I don't know what the beams are rated at, but loaded concrete trucks have crossed his bridge several times.

MIke

 

[workinallthetime]

redneck engineer here,lol.
I once built a bridge for a massy 175 that had a FEL and BB on it (alot more weight then a CUT). The span of the bridge was about 20 feet over a creek that was always flowing. The bridge was about 5 feet in the air and i used large rocks for my piers on each bank and a 24" concrete culvert in the middle. I dont know the technical term for what each piece of the bridge is called but the pieces that span the 20' length were 4 telephone line poles cut to length, I used cabels to bind them together, I then used new 2 x 10's to go across the top of the poles. The poles were not the little ones, they were from where a main line went above the property holding multiple lines to and from a sub station i guess.
I did have the insight to build a dead man and chain the bridge to it, when we had a large flood come through it picked the bridge up and set it down on the bank. After all that work i tore the thing down and built a dock on the pond out of it.
I think i had about 200.00 in the entire project, poles were free and so were the cabels and clamps. scavangers some time make some cool stuff!!
I now drive my b3030 over a small bridge, about 8 feet that is made from bridge timbers and 2 x 10's. cost 0.00

 

[sandman2234]

A flatbed tractor trailer with the wheels removed after you get it in place would work. A drybox or reefer would also work if you just removed the doors and cut the front out. Might want to brace the sides so the wind doesn't do it in, since the front and doors offer some strength in that area. Cutting it down isn't my idea of fun, and the higher sides offer more strength, whereas the roof will give you somewhere to run to when your caught outside in the weather.
David from jax

 

[dillo99]

I built a wooden bridge that spans about 12 feet. Used 2x12x14's (4 of them) and then used 2x10s for decking. It is very sturdy. My cut with backhoe weights about 3,000lbs.

 

[EddieWalker]

Since you mentioned cheap, then logs from your land are about as good as anything else. I'd use Oak or a hardwood if I had them. Probably use four of them as over kill and put two side by side where the tires will put all the weight. I'd also cut them so you had allot of overhang on either side. At least ten feet. With a 12 foot span, I'd want the logs 32 feet long.

Then I'd deck them with PT 2x6's or bigger. I've never done the math, but I'd check to see what the price is per square inch of PT 2x8's, 10's and 12's.

The problem with the trailers and other metal existing contraptions is the amount of fabrication that will have to be done. As soon as you start removing material from it, you loose allot of strength. The only trailer you should consider is a flatbed. Finding one will be a challenge because so many people are looking for them. It could easily cost many thousands of dollars for a used, beat up one.

How steep are the banks? Pouring concrete across the bottom and letting the water run over it is a very common method for crossing creeks. If the water it too high, you can't cross it, but if it's just a few inches, you can still drive through it on top of the concrete.

Eddie

 

[MarkV]

My cheap solution for crossing a 10’ stream with a 7500 lbs tractor are the ramps from an auto garage car lift. Found a pair for $200 and they work great. Maybe an ad in the paper would come up with some.

MarkV

 

[crbr]

I use a screed screen from an old rock crusher found at a quarry going out of biZ. Most excellent.

 

[crbr]

My cheap solution for crossing a 10’ stream with a 7500 lbs tractor are the ramps from an auto garage car lift. Found a pair for $200 and they work great. Maybe an ad in the paper would come up with some.

MarkV

I know a guy that found a set and placed them over the edge of an embankment (that he dug out). Access from the lower side of the embankment gave him access to under a vehicle, where the vehicle drives onto the ramps from the top side. That was his answer to a lift.