building a bridge.

[gayler]

I'm thinking of replacing an aging bridge over my backyard pond. The one I have now is wood and I would like to build one with a metal frame. Its twelve feet long and three feet wide. Its only a foot bridge and will support maybe three adults at max. It will have a slight arch to it. I'm thinking of using two inch square tubing for it. I need ideas on how to bend it. The top beam will be arched and the bottom will be straight with bracing between the two.

 

[larry_g]

I built a garden arch this year and when I ordered the material I had them bend it to the radius I specified. So talk to your metal supplier.

 

[ilovevocs]

You can bump it or roll it. Both take the right tools. I would call a small fab shop and see what they would charge you. Unless you want to invest in the tooling. Swag makes a ton of accessories for the HF roller.

 

[Toofast28]

I wouldn't use tubing, traps moisture, it'll rust from the inside out. Use a 4 inch channel for the bottom. I believe 2" tubing is too light for the bottom, you'll have a lot of bounce in it regardless of wall thickness. As mentioned above your steel supplier should be able to roll that. If not you can get a fab shop to make it. Personally (because I don't have tooling to roll/bend 4" channel) I'd cut the channel every 6" or 12" (but not the top flange) take a small/thin triangle out, bend it, weld it back together, diamond plate the inside of the weld. I assume it'll get a wooden deck, you can manipulate the wood to get a perfect radius if you were going for a full round look.

Do you plan to build in place? Or build and set in place?

 

[gayler]

I wouldn't use tubing, traps moisture, it'll rust from the inside out. Use a 4 inch channel for the bottom. I believe 2" tubing is too light for the bottom, you'll have a lot of bounce in it regardless of wall thickness. As mentioned above your steel supplier should be able to roll that. If not you can get a fab shop to make it. Personally (because I don't have tooling to roll/bend 4" channel) I'd cut the channel every 6" or 12" (but not the top flange) take a small/thin triangle out, bend it, weld it back together, diamond plate the inside of the weld. I assume it'll get a wooden deck, you can manipulate the wood to get a perfect radius if you were going for a full round look.

Do you plan to build in place? Or build and set in place?

I plan to build and set in place. The old one was all wood and I had to move it and set in place A couple of two wheeled carts made it easy to move.

 

[BLUE72CAMARO]

Definitely not arched like you are looking for but this a bridge I built for a drainage ditch on my property and can be done fairly cheap if you find a couple bar trusses leftover on a job somewhere.

Scroll to the bottom to see the bridge a lot of debate on the first page and a half about how much weight these two trusses would hold.
http://www.garagejournal.com/forum/showthread.php?t=260849&page=2

 

[gayler]

Definitely not arched like you are looking for but this a bridge I built for a drainage ditch on my property and can be done fairly cheap if you find a couple bar trusses leftover on a job somewhere.

Scroll to the bottom to see the bridge a lot of debate on the first page and a half about how much weight these two trusses would hold.
http://www.garagejournal.com/forum/showthread.php?t=260849&page=2

That is cool! I never thought about doing a bridge that way! Even better than what I was going to do! Where do you find these?

 

[BLUE72CAMARO]

My dad got those off of a jobsite at a strip mall. They are used under all flat roof structures like that. They order spares when they buy them and these were headed to the scrap yard had he not got them. With that said you may call your local scrap yards and see if they have anything like that laying around.

 

[Farmall 1066]

Overkill for what your doing, but a neighboring town has a footbridge through the middle of a park made from an old dragline boom.
Always admired that repurposing!

 

[NUTTSGT]

My step-dad's parents had an orchard across the creek from their house. IIRC, the bridge was built using rail road rails with native cut 2x4s (creosoted) for the bridge decking. I remember as a kid them rebuilding it and the deck being off of it. Knowing what I know now, I'd guess the rails came out of the stone quarry where my step-grandfather was an electrician.


EDIT: I guess seeing that as a kid, has always made me want to build a bridge over a creek. Nothing huge but just so I could say I built it.

 

[laser3kw]

:Edit:

whoops wrong "Rockford"
I was thinking Rockford Illinois

 

[Bondo]

Definitely not arched like you are looking for but this a bridge I built for a drainage ditch on my property and can be done fairly cheap if you find a couple bar trusses leftover on a job somewhere.

Ayuh,.... Bar joists are Great ain't they,.....

I built a twin finger docks, 'n water front patio outa 5, ole 2'x 30' bar joists,....

Built a yard wagon for my houseboat outa a pair of 18"x 24' bar joists,....
couple a house trailer axles, 'n a pile of ole steel,...

 

[BD1]

Try craigs list maybe under , '' Material '' or '' General'' even the '' FREE ''

 

[tractordude]

Overkill, but a friend used a 53' ft semi trailer frame.
You can drive almost anything over it within reason

 

[Sureshot]

I built one that size using 2" square tubing and didn't use a bottom, just the arch. I tacked the two lengths together side by side and cut them part way through so I could bend them. I didn't cut enough slits the first time so I just cut more until I got the arc I wanted. I added angle iron to the inside to screw the boards on from the bottom and four 2" crossmembers to run railing supports off of. For the railing supports I bent 3/4 rod and welded them to the cross pieces. The top of the rails had 3/4 inch cedar over the top screwed from the bottom through flat plates on top of the 3/4 bar. A stip of ceda screwed to the bottom edge of that hid the fasteners.

 

[Sureshot]

Here is the only pic I could find. The ex-wife walked a horse across it for some unknown reason and it held so multiple people would be fine. It would have looked much better had she maintained it.

 

[jimgood]

Bending tube by hand:

It's only an 1 3/4" but makes 2" seem doable.

 

[PugetDude]

Here are a few ideas; might as well make it look interesting as well as functional.
Inverted Bowstring Truss bridge:

https://www.google.com/search?q=inv...qYTKAhUT8mMKHQIyB8EQ_AUIBygB&biw=1600&bih=706

 

[BUGTHUG]

You might look for old metal buildings that they tear down, some of them have a round truss system. There are usually some listed on CL. In fact you might look in Missouri (after the water goes down), usually they have big turkey buildings they part out all the time.