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OB Engineers: Steel Beams to Make a Bridge
We have a steep, nasty creek at our farm that basically cuts off 1/4 of our place. We have a low water crossing that worked well for years. But lately has begun to be a problem. A combination of high MS Rivers and silt, and a moving bank. Basically it's time for a bridge.

From bank to bank it is about 75 feet across (and about 12-15 feet deep). I had a guy come out and quote me an 89 foot railcar bridge, installed, for $26,000.

I am looking for cheaper options. I was looking at used steel beam prices. And basically they are pretty reasonable in the 50 foot range. Any longer than this and they go way up in price, plus they become expensive to haul. I found some 50 footers for about $650 each. (12 inches and 55 pounds per foot if I remember correctly).

I am thinking about buying four of the 50 footers. And joining two of them together with some sort of fabricated jointing plate? That would give me two 100 foot beams. Dig some footings and pour some concrete to anchor them with about 10-15 feet of overhang on either side.

I would place them about 7 feet apart (about the width of tractor or pickup truck stance). And then deck the bridge with some 10 foot 3"x10" pine (treated) timbers that I would have custom cut.

I'm only looking to support pickups and ATVs. With the occasional tractor hauling a fertilizer buggy (tractor, buggy, and payload would weigh max of 20,000). So maybe something rated to 25,000 to 30,000. I do not need to support log trucks or heavy equipment.

Two basic questions:

1) will this idea work?

2) how do I make the calculations for how large of a beam I need? Is there a simple formula for this?


bbvdd
Alabama Fan
Memphis, TN
Member since Jun 2009
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re: OB Engineers: Steel Beams to Make a Bridge
I’ve seen people use a house trailer frame but you’d need to be careful about what you drove over that with. Also, not sure if that would get you to 75 feet or not.


civiltiger07
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re: OB Engineers: Steel Beams to Make a Bridge
I looked at doing the same for a guy a few months ago. Spanning that with a single beam is hard to do with not other intermediate supports.

A truss is a much more efficient member to span that in one span, but that involves some series fabrication.


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jimbeam
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re: OB Engineers: Steel Beams to Make a Bridge
quote:

OB Engineers

Hey
quote:

Make a Bridge


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490
Ruxins Rascals
LSU Fan
Middle of Da Bayou
Member since Nov 2018
325 posts

re: OB Engineers: Steel Beams to Make a Bridge
@ 75 ft it would be nearly impossible to span with a wide flange. You will have to use a truss at that span.
This post was edited on 2/10 at 7:33 pm


junkfunky
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re: OB Engineers: Steel Beams to Make a Bridge
Not gonna happen. You're talking about an expensive splice connection and the beams are gonna deflect a lot just under self weight. You need depth for your beams, not weight.

Like someone said above, truss will require less material but more fabrication.

Any way to drive some timber piles for intermediate supports?


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re: OB Engineers: Steel Beams to Make a Bridge
quote:

You will have to use a truss at that span


Ok. I think I know what a truss is. But I'm not entirely sure what a truss is....

Even if I could find trusses 100 feet long (like where they're tearing down a building or something) how would I haul them?

And, old railcars are 89 feet long. And they just drag them into place and they're rated for 180,000. Aren't they just steel beams?

I'm trying to support basically just pickups and tractors. 20,000 pounds total weight. Not log trucks.


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Ole Miss Fan
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re: OB Engineers: Steel Beams to Make a Bridge
quote:


Any way to drive some timber piles for intermediate supports?

Sure. But that would pretty much defeat my budget I would guess.

quote:

truss will require less material but more fabrication.


So, can I get two trusses and fabricate them together?


Ruxins Rascals
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Member since Nov 2018
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re: OB Engineers: Steel Beams to Make a Bridge
Trying to keep the budget in mind, I don't see a way that you will be able to span 75 clear feet for less than the price you were quoted. With that being said i would also be hesitant to trust an old rail car with supporting 10 tons at that span, but that may just be the conservative engineer in me. Perhaps another OBer will chime in with some more insight into other options. If no answers come by the morning I will take a look when I get to my steel manual tomorrow.


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Ole Miss Fan
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re: OB Engineers: Steel Beams to Make a Bridge
quote:

would also be hesitant to trust an old rail car with supporting 10 tons at that span

Those railcar bridges are the tits. They are rated for 180,000 pounds. I have run hundreds of fully loaded log trucks over them. Even tri axel drop decks hauling D7 Dozers overweight. No problem.

quote:

take a look when I get to my steel manual tomorrow.


Many thanks


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Hermit Crab
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re: OB Engineers: Steel Beams to Make a Bridge
Could you dig a ramp down from ground level to creek level so the span is shorter?


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civiltiger07
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re: OB Engineers: Steel Beams to Make a Bridge
Are you sure these rail car bridges that support 180,000#’s are spanning 75’? From what I have found a standard railcar is around 50’ long.


TheDrunkenTigah
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re: OB Engineers: Steel Beams to Make a Bridge
I’m the wrong kind of engineer but I’m wondering if you couldn’t lay down shipping containers and then cut holes in either side


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re: OB Engineers: Steel Beams to Make a Bridge


civiltiger07
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re: OB Engineers: Steel Beams to Make a Bridge
That is what the railcar can carry on rails. You are talking about doing something completely different with it.


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re: OB Engineers: Steel Beams to Make a Bridge
quote:

You are talking about doing something completely different with it.

I understand. These are the standard bridges used by the major timber companies to access timber on their land. I used to be in that business and I can tell you that Weyerhaeuser and Plum Creek and International Paper had hundreds of these on their property. And they have collectively run hundreds of thousands of fully loaded trucks weighing close to 100,000 pounds.

I am trying to install something that will support 20,000 pounds. So, basically, I am looking for something lighter and hopefully cheaper. I totally understand if you wouldn't be comfortable driving over it.


civiltiger07
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Member since Dec 2011
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re: OB Engineers: Steel Beams to Make a Bridge
I have no doubt they do run trucks over bridges like that. I just bet they aren’t 75’ spans.

Sounds to me like you need to talk to the guys you worked with in that industry. I’m sure they have some go bys for spans and allowable loads.
This post was edited on 2/10 at 8:14 pm


AUCE05
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Member since Dec 2009
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re: OB Engineers: Steel Beams to Make a Bridge
Post me a photo of the crossing baw.


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No Colors
Ole Miss Fan
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re: OB Engineers: Steel Beams to Make a Bridge
LINK
Here's an article published by the Iowa Dept of Transportation about how they are using 89 foot railcars on public roads as a low cost substitute for concrete bridges.

I didn't read it to see how long of a span they were crossing. But if they can use them for public roads, then they're overkill for me.


White Bear
USA Fan
NWLA
Member since Jul 2014
5213 posts

re: OB Engineers: Steel Beams to Make a Bridge
How will you keep the bank from eroding from beneath the bridge? A retaining wall? Tank car culverts are too small/the ravine is too deep?


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