Deck weight capacity

[rd_macgregor]

I'm not sure is this is the right place to ask this, but here goes...
I have been looking for a truck or trailer deck (or "flat rack" container) to use to replace an old wooded bridge.
I recently saw an 8' X 18' truck flatbed for sale that might do if I first cut off the cab protection (vertical) part of the deck.
My question is, how do I tell if this is structurally strong enough for my use, if I support it near the ends with, say, a 16' span? I want to be able to drive my tractor, with implements across it, maybe a loaded log trailer, dump truck or other heavy equipment. I figure I'd need maybe a 20,000 lb capacity, more or less, just to be on the safe side.
Any suggestions?
Thanks,
BOB

 

[rus_geek]

Measure the main frame members of the bed and you can calculate their bearing capabilities, assuming you can also properly guess the type of steel used.

 

[Diamondpilot]

I would not think a truck flatbed would be strong enough. I had a 25,000# GN trailer and it had 10" I beams or maybe 12", I can not remember. You would need something this strong atleast.

For only 16' I would get some rough saw white oak or even some used I beams and place them on concrete peers and go from there.

Chris

 

[RedRock]

Not a bad idea if it holds the load over time, a pre-built bridge ... since it doesn't matter how bad the tires or axles are, I'd think you could come out for less $$. I'm interested to see what you end up with as I have lots of ravines and will need to span a few areas myself in the future.

 

[rd_macgregor]

I haven't actually looked at this yet or taken any measurements, but I should have included this link (note that the hay cart underneath isn't part of the truck bed:
18ft flatbed - Charlottetown Farming Equipment For Sale - Kijiji Charlottetown Canada.

I did a lot of research on shipping containers and determined that what I really wanted for my replacement bridge was a "flat rack" container. These have the same strength as a regular container but lack the superstructure (they just have vertical ends (sometimes collapsible). Sadly, they are not as readily available (I found a couple of 40-footers in New Brunswick for $3k apiece, but didn't want/need 40' and couldn't figure out how to get them shipped here... plus, I didn't want to pay that much!
That's why I started looking for alternative, prefab options, like truck/trailer decks.
If I find one that is strong enough, my plan was to have a local contractor pile-drive pairs of I-beam columns on each side of the stream crossing and weld the bridge to I-beams welded across these supports (an inverted "U" under each end of the bridge).
For all this trouble, you'd think a big culvert would do the job a lot easier. The problem is that the local environment dept. folks get a lot more heavily involved if you start mucking around in the stream bed.
BOB

 

[BruceWard]

Here is the picture

Based on the ratio of outside channel height to tire height I believe the outside channel or tubing is 8" and the inner support members are 12".

It looks plenty strong to me.