re: OB Engineers: Steel Beams to Make a Bridge

I’d drive some sheet piles to stabilize the bridge. We’ve had same problems at a couple places I hunted. The one in Port Gibson we dropped in some large OD pipe and spanned across it. It took one major rain, and a little debris in front of culverts and it washed out around them overnight. That sandy soil is terrible.

Bad choice there. Offspec concrete spans will be terrible.

Rail car bridge is likely cheapest metal span one can find.

I priced a bailey bridge, pioneer, and another brand for work at like a 80ft span and it was a pain. They did not like going over the 50-60ft range. The bridge alone was over $100k for cheapest option, that didn’t count the ringer barge crane that set it.

If you can put a few pile groupings in the creek and shorten the spans to like 25 ft you can build entirely out of wood or use your steel beams and put a deck on it. That’s more work than the rail cars.

You will need one hell of a foundation for the railcar, maybe even pile supported foundation to make it last.

no way a 12" beam will span that distance. i know highway work is designed for a lot more weight but a span that long your talking at least several 36" steel beams for that span. I know the rail car seems expensive but it probably your cheapest and best option.

if you want an erector set look up Acrow bridge ( acrow). This is what they used on the interstate after Kartina but i think they were are typically +/- 60' spans. They have some used ones for sale here ( eifel trading) sometimes. or they do have used trestles for sale per pound but again the span in not going to be more than 60' at max.

Technically, you could span 75' with W12 "beams" but not just 2. You would need more, spaced closer together. I don't think you're gonna be able to compete with the flat car idea unless you have a connection to get several more "beams" at a very cheap price.

If you could install a support in the middle, it would help a lot, but that would require driving a couple piles, which will take the price back up.

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

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Not really, but if you happen to know a structural engineer, or may even a 3rd or 4th year student, you could probably get the calcs done for maybe some beer money. You're gonna need to somehow tie those deck timbers down also.

75 feet is a long damn way! Good luck, but I just don’t see a homemade bridge being way to go. 12 foot is a long way to fall

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Got to my steel manual, with 2 stringers you would need W36x853 (853lb/ft) or 3 stringers, W36x529 (529 lb/ft).

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Yikes.

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drive some pilings down and then build a wooden bridge

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You will be very limited in span length due to the length of timber stringers readily available. You would probably be looking at 4 spans.

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I am thinking about buying four of the 50 footers. And joining two of them together with some sort of fabricated jointing plate?

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Not an engineer, but this does not seem like a solid plan.

check a local fabrication shop, especially if they do industrial work.