Another Bridge Project

[meadowlarkponds]

I need to build a bridge to cross a wet-weather creek that most of the year is at best a trickle but can on occasions be a raging torrent of water.

The bridge will be used by my tractors and a small Case 450 dozer.

The county recently re-built a bridge on my county road leaving the old bridge materials for the taking...and I helped myself, along with a neighbor who is also building a bridge.

My inventory of "free" lumber is the following: eight 10 inch by 10 inch by 16 feet treated bridge timbers, about twenty roughly 3 inch by 10 inch by 12 feet treated boards, and four very large diameter short poles, like telephone poles. All the lumber, especially the large timbers, appears to be in great shape.

I'm looking for advice on how to anchor the bridge and if the timbers are adequate to support my equipment?

The creek span can be easily accomodated by the 16 foot timbers and the chosen location of the bridge is at a very shallow flat part of the creek.

My thinking is to set the large poles in concrete on the downstream side of the bridge to help hold it in place during the "100 year" rains which we get about twice a year.

Any suggestions for anchoring this bridge and any thoughts on the ability to support my equipment would be much appreciated. Thanks in advance for your thoughts.

 

[MarkV]

Would it be possible the mount two poles in the stream bed with a beam on top to cut the span of the timbers in half? I would think that the 10 x 10’s could hold a pretty good load. Just as a reference I cross a similar stream bed with a 7500 lbs. tractor on ramps that were originally for an automotive lift.

What does the dozer weigh?

MarkV

 

[meadowlarkponds]

MarkV,

I think the dozer is about 6 tons. It would be difficult to set poles in the stream bed, but I guess I could do that if it is necessary. The drop to the bed from the bridge isn''t much in this particular location...I'm going to guess only about two feet. I was hoping that those 10 inch timbers would be enough to hold the weight of the small dozer. I'll go out and measure the actual span, in terms of length which the timbers would be unsuppported, but I'm guessing its about 8 feet.

In addition to the span concern, I'm also worried about the bridge getting washed away in our typical huge rainstorms. Appreciate any thoughts on that.

 

[MarkV]

I have heard of people chaining their bridges to large trees or anchor points so if high water were to move them it would not be to far. I would guess the best way would be concrete footings of size that the bridge could be bolted to but remote bridges can be hard to get a concrete truck to.

Good luck,
MarkV

 

[meadowlarkponds]

My guess was right...its an 8 foot span in which the timbers would not be supported.

There are a couple of trees that would be good candidates for anchoring the bridge..since the trees survived a 12 inch rain in one 8 hour period earlier this year in which the creek became a huge raging river, they would probably be pretty good anchors...I've got some heavy steel cable which should work well for that.

Will eight 10 inch square timbers with heavy lumber tieing them together support 6 tons accross an 8 foot unsupported span?

 

[bx24]

I don't know how well either of these suggestions would work, but how about an old POS tractor trailer flatbed?

My other suggestion would be to buy a couple of loads of large softball size rip wrap and simply have the water flow over the top of the rock

Good luck

 

[Western]

My brothers FIL had the same issue in the 80's. Full time creek 30 foot across, banks about 5-6' occassional flooding over bank during spring rains.
Being a truck driver he located a flat bed trailor I think it is 42', cut the wheels off and drug it over with neighbors backhoe and drove it back accross.
he put 2 steel pipe on up stream side and welded about 1 foot of heavy chain to keep in place, I have driven over it a 100 times. My brother was up there last week hauling hay over it with a big tractor. doesnt seem very wide but it opened up 200 acres to access. doesnt even flex when you drive that big ole case (140hp 2290) over it. been there almost 20 yrs.

 

[Western]

Forgot...he welded steel plate over the top about 10 yrs ago..

 

[EddieWalker]

Meadowlark,

I'm not qualified to tell you what will or wont work, but I'll offer a few thoughts and suggestions that you might look into to see if it's possible.

I don't remember if you ever bought a trackhoe or not, or if you have access to a backhoe. If you can get one, I'd dig out some nice deep footings on either side of the creek that went at least three feet below the bottom of the creek bed. I'd also be sure to have a trench going back into the bank away from the creek on either side to anchor the footings into solid material.

I wouldn't set any posts into concrete, but would rest them on the concrete with ties that are set into the footings. Simpson has all sorts of ties that would work good for this. The idea is to have gravity do all the work and the ties to just hold the beams in place.

The beams will be the weekest at the middle. I'd strengthen the middle by setting a post at the base of the footing that angles out to wards the one third point from the anchor point of the beam for both sides.

Not knowing how strong those beams are, I'd put two close to each other so they support the tracks of the dozer on either side. Four beams at a minimum with a fifth one in the middle should be pretty good. Maybe. hahaha

Decking should be OK with PT 2x lumber perpindicular to the beams. To get more strength, you could put it diagnally 45 degrees. Then put another layer of decking right over the beams for the tracks to tear up when you cross the bridge with the dozer.

How much concrete you'll need is probably the biggest mystery after what the beams will hold. It sounds like a fun project, so if you do it, please post some pics.

Eddie

PS, are you gonna make it to the get together in October?

 

[meadowlarkponds]

Eddie,

Thanks for your ideas...I was hoping you would chime in. I have a back-hoe, but the area for the bridge is kind of difficult for any equipment maneuvering. I will try to clean and smooth things out with the dozer first and then maybe I can get the back-hoe in there to dig out the trench as you suggested.

I've got 8 large timbers, all in very good shape. My plan was to put three together on each side of the bridge to suport the dozer tracks and then use the remaining two spaced pretty much in the middle. I'm thinking about 10 feet total width with the track supporting beams covering three feet in on each side.

The decking lumber, courtesy of Polk County, will be rough cut treated lumber which is something like 3 inches thick and about 8 inches wide and 12 feet long. I've got plenty of that to cover the 10 foot width of the bridge all the way across the 16 foot length of the timbers.

I'm not sure I understand your comment on how to tie the timbers into the footings?? Simpsons?? Sorry to show my inexperience, but I just haven't done any of this before...and of course I'd like for it to last.

I'll take some pictures....but I don't expect to start work until the stream nearly dries up or significantly reduces the flow. We are finally getting some dry conditions so maybe in another two or three weeks I'll start construction.

October visit sounds like a great idea. I would love to see your lake spillway full and also see what other accomplishmnets you have engineered since my last visit. Thanks again for yours and everyones comments.

p.s. my dozer is currently in the shop getting a track job...man, a dozer is an expensive piece of equipment, but you know that very well.