Need to build a 25' tractor bridge across creek

[deanfitz]

New to this website. My project is a 25-30' bridge across a creek in the woods on our property. I have a 1/2 mile of property, I can't get to with my tractor. I have access to a D5 dozer next door where their digging a gravel pit and dump trucks can/will haul dirt over to the bridge location. The location is on the Bogue Chitto River in La. and it floods in winter usually. I know the highest water line and its about 3' above the access road to the bridge location. The bridge WILL go under during these periods( unless I build it high up), only access is by boat then. The current during high water levels is moderate, and has washed out a couple of "Rinky Dink" bridges before. One being made of concrete and buckled in the center. The pieces are still at the location. Also, We made temporary bridge next to the site with a culvert and dirt, the dozer can cross this bridge. I've contacted a local power company where they are replacing many(1,000's) of light poles after hurricane Katrina and many are in near new condition. They will sell for 10ct a foot.
I planned on using about 6 poles with a abutment footer on each side of the creek 12'Wx6'thick & 8' deep and standing poles up inside the cemented abutment and cut flush with the poles lying on top of the cement footer.
MY QUESTION IS: Is that too long of a span for these poles?
Does anyone think I should use Some sort of /\ joists to help support the center. I was hoping not to, so the debris would not build up so bad.

Any/all ideas welcome. I have included some "rough draft" (not to scale) pictures to show my plans.
I have a 45hp Mahindra w/loader and 1/2 pickups that want to cross bridge to where I'm building a camp (at a future date)

BE SURE TO USE THE ZOOM TOOL WHEN VIEWING PICS.
http://s785.photobucket.com/albums/yy139/deanfitz/

Thx, Capt Dean

 

[CurlyDave]

I think you need to talk to a professional engineer.

My gut tells me that the poles are not really up to this task, but I have been wrong on that kind of thing before.

 

[deanfitz]

Thanks, Curly
Did I mention that the draft I'm using is a replica of one that has been there for 28 yrs. It is about 14 miles down river, I have seen it but have no pics. They cross it with everything, even a mobile home.
Thx, Dean

 

[scoutcub]

Dean;

I'm looking to something like this in the future, but was planning on 10 or 12 poles/trees across...then plank across the top. Even that I'm not to eager to ease my 10 ton dozer over, not the mention the 15 ton trackhoe. A center support would cut your needed capacity in half, and if the tracks could span the end abutment and middle saddle, you'd be set. Figure a D-5 depending on model, is anywhere from 22K to 30K lbs...... might be time to sit down with a structural engineer!

 

[MikeD74T]

deanfitz, Keep in mind that wood bridges can become rafts in high water. You might be better to spend on steel than have your wood bridge float away. Our snowmobile club has pole bridges of similar span that carry heavy trail groomers without issue. MikeD74T

 

[deanfitz]

We are planning to wrap the poles with cable and anchor to the concrete footers. Plus, the cross 4x12" planks with be lag bolted to the poles standing in the concrete footers. This bridge is only going to need to support 1/2ton pickups and a 45hp tractor sometimes. I'm thinking 5,000 lb max.

 

[scoutcub]

Oops, sorry I thought you were wanting to get across with the D-5.....it sounds a whole lot better now!

 

[LD1]

I am thinking that utility poles would not be up to 5000lb loads.If you are using 6, then each one will need to be able to support the planking, as well as 1000-1500lbs right in the middle. A 8-10" round wood pole that is probabally southern yellow pine, is not a safe bet IMO.

When I was sizing beams to support an upstairs in my pole parn, which needed to span 30ft and be capable of the 1000-1500 lb load in the middle(to yank engines and such), and just light storage above, A w10 x 19 I beam was minimum. Price for two was ~$900. I started looking to go the wood beam route. That would have required a 4 x 16 on edge minimum. And I dont think a utility pole is near as strong as that. Since you are talking similar loads and an even steeper penalty for failure, I'd go with beams. I ended up using w12 x 35, as I got them used a a great deal.

And since you are already talking roughly $5k Just in your concrete footers, why skimp on the rest?

 

[RickB]

The live loading is one thing, but withstanding flooding forces will be the real engineering challenge. Perfectly good telephone poles snap off from straight line wind loading all the time.

Free advise is worth exactly what you pay for it.
Folks that are willing to spend thousands of dollars and countless hours on a project without spending a few hundred on professional advise simply amaze me.

 

[Transit]

If your creek has that much of a flow under server conditions then I would expect that the underling structure will clog with debris and you will be in effect building a dam. I would be talking with an engineer and be mindful of any waterway, EPA regulations before you turn a spade of dirt.