Load capacity of railroad ties

[RobA]

Eddie,
I see your point. I guess the design you were talking about would look like a railroad track. The support beams reaching across the creek are sort of like railroad tracks and the bridge deck goes across them sort of like railroad ties.

There is a culvert in the creek right now. However, it is washed out as I believe it was installed incorrectly by the previous owner. The culvert is only 9 feet long. If I reinstall it i don't think it would be wide enough for my tractor after taking into account the sloping side of the dirt covering it.

I have posted here about this before and have had myself convinced that a culvert would work, then that a bridge was doable, then a low water crossing .........

I guess they all have their drawbacks.

What if I were to use pressure treated posts instead?

 

[EddieWalker]

The basic obsticles your going to have wtih a bridge are twofold.

First, creating a foundation to support it along a creekbed where moisture and movement are factors. The varialbles are unique to every location. Depending on you soil and weather conditions, will determine how deep and how wide your footings will have to be for you load.

The Second obsticle is the amount of span you wish to cross. A short span requires little engineering. A few feet and the stregth of some thick wood is plenty. Ten feet and you need to use some geometry based on the load it will handle and the material you'll be using.

If you really want a bridge, get something that is way over engineered for it like a railroad car or semi trailer.

To cross the creek on a regular basis for the cheapest, simplest and safest method, buy a longer culvert, or join the one you have with another, or use two side by side.

For a short culvert, there are all sorts of ways to build up the sides to hold fill material. TxDon has metal plates bolted to a short culvert to create a really nice bridge. Welding and pounding rebar to the ends and putting sacks of concrete through the rebar is another method I've seen used quite often.

Good luck,
Eddie

 

[TN75Jason]

Rob,

The design that you describe is very similar to a bridge that I use across a creek in my hayfields all the time. The railroad ties are laid side by side perpendicular to the creek forming a structural deck with a total span equal to the length of the ties - approx. 10 - 12 feet. I drive my NH TN75 with loader and all four tires full of water pulling a round baler (complete with 1000 lb bale) across it all the time - total weight approx. 12000 lbs. Of course, the total tractor and baler are not entirely on the bridge at the same time.

Jason

 

[RobA]

Jason,
Any chance of posting a pitcure of your bridge?

Rob

 

[have_blue]

Jason,

That's a testament to the strength of cross ties! Your wheels are on only 1 or 2 ties at any given time. Do you see very much sag as you roll across?

Have you thought of laying treated 2x6's across them to distribute the load? They wouldn't even need to be attached with HD fastners... just nailed down to keep them from moving. Leave a 1/8" crack between them to let the water drain.

 

[rambler]

Rob, I understand your design plan, but I've never ever heard mention of the most important measure - what is the span of your bridge? How long across? It must be 10 feet or less, or you couldn't use regular RR ties?

You are going to use a lot of ties, and are asking 3 of them to support the weight.

A better design is to make your foundation on each side. Instead of planting rr ties that rot out in 15-20 years, use concrete - you can use one rr tie as a sill along the top. For pilings for wooden tressles, a different wood & treatment was used, a good newish rr tie lasts 15 years or so planted in the ground.

Then lay a solid layer of rr ties across the span, side by side. This will give you what, 15 or more rr ties crossing the water? You can deck over the rr ties with 2x pressure treated, and it will be much stronger with all those rr ties supporting your load. The cross decking will spread the wheel track to most of the beams, making a very strong bridge.

In your plan, you have only 3 beams supporting the load, with the weight of 15 or so 200 lb rr ties already on the span! Not so good.

The danger with only 3 beams of wood, is when one rots or splits or has a defect you didn't notice..... Not good.

I'd prefer concrete ends & I beams across the water & then the rr ties for decking. We have 2 such bridges on my small farm across the ditch, perhaps a 16 foot span, I forget. Taking a loaded combine across, nothing has moved or cracked. The I beams are pretty close.... That's 20-25,000 lbs with a cornhead & full grain tank pretty much balanced on one axle...... My point is, when dad built these in late 60's and early 70 he planned on using only his Oliver 88 & a 100 bu wagon to use them - 6-8,000 lbs on them at any time. Do _not_ skimp or build a bridge with anything at all near the maximum load in mind. You will be doubling or tripling what you drive across it in 3 years. Trust me on that. You will.

Never build a bridge too light, it is more dangerous than the other thing we all do - build a shed too small. /forums/images/graemlins/smile.gif

Wood & dirt & water just never lasts long, and 15 years flies by. For the work involved, do it right, or do the water crossing.....

--->Paul

 

[RobA]

Rambler, the span would be about 12 feet. The guy who is selling the ties has them from 8 to 14 feet. The 14 footers must be switch ties. I guess I have been trying to take the easier route by not pouring concrete. I have a post hole digger so I could do an all railroad tie construction pretty easily by myself and with minimal materials.

Your bridge design sounds ideal. I like the idea of concrete footers but it would not be easy to get a truck to the site. I could rent a gas powered cement mixer but I am not sure where to get I-beams or how to attach the decking to it.

Any chance of a picture of either of your bridges?

Rob

 

[Slamfire]

Have you thought about using railroad track as the beams across the span? My granddad had a couple of pieces of 120 lb rail covered with 3" oak planks that he drove across with 2 shires and whatever they were pullin'. My dad used the same bridge for his 8N and whatever it was pullin'. Come a flood we'd have to go down stream and recover the planks, but the track stayed put.

 

[rambler]

</font><font color="blue" class="small">( Have you thought about using railroad track as the beams across the span? My granddad had a couple of pieces of 120 lb rail covered with 3" oak planks that he drove across with 2 shires and whatever they were pullin'. My dad used the same bridge for his 8N and whatever it was pullin'. Come a flood we'd have to go down stream and recover the planks, but the track stayed put. )</font>

If he has to buy, good old used I beam would be much better, rr track is designed to be supported every foot or so & bends under load, I beam is engineered to use for spans. The I beam will hold a lot more weight, lb for lb. Now if he has 4 pieces of track laying in the grove, well then, you use what you have. /forums/images/graemlins/smile.gif

--->Paul

 

[TN75Jason]

RobA,

Sorry about not answering your question - I have been out of town for a few days. Yes, I can take a picture and measure the size of the crossties. I may need some help in how to post a picture on the website, though.

And I agree with Bob (have blue) - it is not an ideal set up to have the entire wheel load on only a couple of ties. As a civil engineer, I would have built the bridges differently using the same materials, but my neighbor built them and I have just been using them. The relatively short span and the flexural stiffness of the ties make it work - I do not notice any deflection as I cross.