Building a bridge to cross stream

[spo307]

I need to build a bridge to span a stream 34', tractor with back hoe weights #7500, so I figure 10k lb bridge, the deck i would probably use 3' x 10' subway grating either steel or galvanized. the easiest thing to do would be get a 40' flat bed trailer ( full rails front to back ) take the axles off and 5th wheel, drop into place with the 200 excavator and be done. i have seen flat beds for 3K, the i thought 2-12" I beams, with the decking on it, or 3 8" beams, anyone know span and loads for I beams, i am a welder just don't know the tech stuff, I know there's a table for calculating it on the web but again, i took a small bus to school. thanks Dennis

 

[Cami]

Engineers are cheaper than failed bridges.

It doesn't matter what bus you took to school, or what you know, because specialist help is just a phone call away. When I run into something I'm not sure I can do properly, you can bet that I call somebody who can; whether it's for advice or for them to actually do it for me.

Is a bridge the only option? Can you make a ford or install a culvert? Is this permanant or just for the duration of a job? Can you rent/buy a Bailey Bridge?

I've made a couple bridges, if you can call them bridges, by making a pair of ramps from two logs lashed together with wire rope. ....but if you're not sure, you need an engineer to tell you how big/what species of a log to use! It's not for the faint of heart but can work in a pinch.

 

[LD1]

There is more to it than just a 8 or 12 inch beam. There are many 8" beams and many 12's and there is a big strength difference.

The beams are designated like W12 x 35 whereas W means wide flange, 12 is the depth and 35 is 35lbs per ft.

A W12 x 22 would not be nearly as stout as a W12 x 35 but they are both 12" beams.

A good program to use is Beamboy. You can google it and it's a free download. I cannot get it to work on my computer for some reason but you may have more luck. All you have to do is choose the beam size from the list, and it knows the modulus of elasticity, section modulus, and all that other engineering stuff.

You select the beam, select the length, and select the load. Then hit calculate and it will tell you the how much the beam will deflect and the how much it is being stressed in ksi and also the maximum bending moment.

When I did the beams for the loft in my shop, @ a 30' span with 100lbs per ft distributed load and 1500lb point load in the center (for occasional motor yank) the minimum I could use using L/360 deflection limits was a W10 x 19. I ended up going w12 x 26 cause I found them at the right price.

Given your 34' span, using two beams with a point load of 5000lbs centered @ 17', just start picking beams in that program that will give you about 1.13" or less of deflection.

 

[inmaestro]

All good suggestions. I suppose if you know the rating of the 40' trailer, and build adequate concrete abutments at each end, your idea could work. Be advised, as others mention, once in place, you own it, and if somebody comes along with a 10 ton load...well, you get the picture.

Best bet, sketch something up and have a local Civil Engineer size the beams for you. A 34' span is pretty long, so you may end up with some pretty deep beams. Like the others state, depth is only one consideration. Weight is just as critical. Don't forget the design of the abutment. Even the best steel W beam turns to spaghetti when its on its side. I suspect you might need a little X bracing, too.

Let us know how it turns out. I got a 7500lb tractor and a little stream I want to get over, too. Best of luck.

 

[CurlyDave]

While I have seen trailer bridges and I know they work, the maximum width is only about 8'. This seems very narrow, especially for a relatively long bridge.

I am old enough to remember Teddy Kennedy and Mary Jo...

 

[ray66v]

Dennis, if your engineering skills have not let you down so far, I say build the bridge yourself.

If you have not done well in the engineering department, or have limited skills, that would be different.

A bridge is the last thing on my, "Things I have built" bucket list. I sure would love to do one.

 

[rambler]

Dad built 2 bridges, they had to be 12 feet wide, 8 feet high for the ditch flow. He made them 12 feet wide, he always regreted that, said it shoulda been 16.

Anyhow, he started with 7 I beams and a couple truckloads of concrete. Put 3x8 home sawn white oak lumber across it.

He built it for his 4500 lb tractors and 2 row pull type combine, and 110 bu barge wagons.

Fortunately he overdesigns such stuff.

Now I use it with big wagons, bigger combine, and a couple years ago the fertilizer applicator misunderstood me & took his big loaded applicator over one. Well, I guess if it holds that.... I think we are talking 12 ton on an axle there....

Anyhow, 30+ feet is a good span. And you are talking a good load. A trailer has wheels not quite to the ends - be sure the span matches the loads you want to put on it. Sounds like a good plan, but - be sure. Overbuild. What happens when you find a good deal on the next size up machine, too good to pass up? Be sure you overbuild.

--->Paul

 

[spo307]

thanks to all for the info.

 

[jayste]

If you do a search on here for bridges I'm sure you'll get more than enough information on builds and engineering technical information. Be prepared for a BUNCH of technical information. I've been impressed by the builds as well as the engineering (and I don't mean train driving) information.

 

[Low Bucket]

Here's 2 bridges built by the same person, and they are well built and nice.

Bridge#1
http://www.tractorbynet.com/forums/projects/146006-building-bridge.html

Bridge#2
http://www.tractorbynet.com/forums/projects/147205-bridge-2-a.html

 

[spo307]

thought you knew me for a minute, i was a locomotive engineer, any how i stopped by the steel place, gave him my Ideas, he came up with a w16x 58, he is going to call me on the price of the beams, and the subway grating, It is looking more like a flatbed trailer, some of them are rated for 80k, so at 7500 to 10000lbs is a breeze.

 

[LD1]

I strongly reccomend you download beamboy. The beam he is going to quote you (which is probabally a W16 x 57) is WAAAY overkill and will cost $$$$. The last thing I would do is to take the advice of the person selling the material, it's just more money in his pocket if he can convince you to go twice as big as you need.

On a side note, about the technical info, I got pleanty comming as I finally got beam boy working, so bear with me.

Some background, Beams are rated for load in two ways,
1. Bending stress in KSI. Most beams are A36, which is 36ksi steel, and you are allowed a bending stress of no more than 24ksi, which has a good saftey factor built right in.
2. Deflection. L/360, which is the length in inches/360. In your case, you are allowed a deflection of up to 1.13"

I plugged some #'s into beamboy and this is what I came up with
Beam............Deflection...........Bending stress..........Max capacity
W12 x 30..........(.991)...................13.2ksi....................5700lbs
W14 x 26...........(.963)..................14.5ksi....................5800lbs
W16 x 26..........(.783)...................13.3ksi....................7200lbs
S12 x 31.8.........(1.08)...................14ksi......................5200lbs

I used a 5000 lbs point load @ 17ft (exact center). Using two beams that would give you a 10000lb bridge. Given that steel is priced by weight, I'd probabally opt for the w16 x 26, as it will be one of the cheaper ones listed and the strongest.

The beam he is quoting you will look like this
W16 x 57.........(.311)..............5.5ksi.......................18,200lbs
His beam would give you a 18 ton bridge.

And if you really want a 13 ton saftey factor, consider the W18 x 50 or the W21 x 44. Both would be a little stronger but save some $$$ due to less weight.

 

[DaveOmak]

Knew a guy who built a bridge using a railroad flatcar. worked well.

 

[spo307]

Ld1 thanks for the info, i could not get beam boy to work on my computer, I called the guy back for a price on w16x26, he said your paying for a 35 foot beam anyway so i would cut it to size at the site. depending on price a flat bed trailer might come out cheaper?? thanks again to all

 

[LD1]

Depending on local prices in your area, usually beams cost about 75 cents per pound.

That would put two of them @ about $1300-$1400, and they would weigh about 900lbs each. Which is something to keep in mind when you are thinking about using a flatbed trailer. A couple of 900lb beams dont require near as large of equipment as a flatbed trailer that probabally weighs close to 10k

 

[spo307]

2-w16x26 beams 35' delivered $1,480.00, steel grating ( for deck ) 3'x24' @$400.00 ea x 4, 8' lenghts $1600.00 + bags of concrete, what ever route i go I will post pictures

 

[spo307]

neighbor across the street has these beams, from a rail road bridge 33' x 20" I would use the 2 best, clean and paint, he wants $500 for 2 beams

 

[RedDirt]

A number of years ago I built two bridges from flatbed rail cars. I believe they were 10' wide and 40+ft long. The rail cars were about $3000 delivered about 70 miles. One we picked with a juice boom (crane) and one was skidded with two D-6 Cats, one shoving and the other winching from the opposite bank. One had poured concrete abutments and on the other I used discarded/surplus highway center barriers the county was selling cheap, bedded on compacted road base then backfilled to within a foot of the top. One bridge used 4x12 pressure treated plank and on the other I used 5" thick concrete running plank (not full width because of weight).

The bottom line for the bridges were in the range of $6000 each about 20 years ago. We put loaded concrete trucks and loaded logging trucks across these bridges. The rail cars are very stout (and extremely heavy...to move and place).

I may be able to find a picture and there is a slim chance I still have sketches and calculations squirreled away somewhere. I'll look if you are interested.

 

[rambler]

neighbor across the street has these beams, from a rail road bridge 33' x 20" I would use the 2 best, clean and paint, he wants $500 for 2 beams

Yea - those 2 bridges dad built across our ditch - has 7 of those type beams for the spans.

Dad liked to be cheap, but he built heavy.

--->Paul

 

[JustGary]

The beam he is quoting you will look like this
W16 x 57.........(.311)..............5.5ksi.......................18,200lbs
His beam would give you a 18 ton bridge.

18,000 lbs is only an 18 ton bridge if he's using two of those beams, which wasn't clear if you just glance at that line. Otherwise, very useful info on beams.

I strongly recommend that you go with a number above 15,000 lbs. for your bridge. Your 7500 lb tractor will not just sit in the middle of the bridge. You'll drive it across fast enough to get some wheel bounce and other dynamics. In other words, the static load on the bridge is only 7500 lbs, but the dynamic load on the bridge is much higher since the load is moving. Stand on your bathroom scale and move your arms up and down to see what I mean.

Factor in the eventual rust, etc. and you can see why you want to start with at least a 2:1 "safety" margin. The cost of overbuilding it now is nominal compared to the cost of a failure later.

Of course, you may have found just the ticket with the railroad beams. More capacity than you can ever use at a price even I could afford!

Regards,

- Just Gary