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-   -   Building a bridge across a small ravine... (http://www.diychatroom.com/f19/building-bridge-across-small-ravine-100268/)

timrec 04-01-2011 06:50 PM

Building a bridge across a small ravine...
 
I am building a bridge to span across a small ravine on my property. I am using 12' long logs (6"x8")that were left over from my log home. They are D logs - flat on one side and semi round on the other. I am placing 5 logs across the ravine. I am making the bridge 6' wide to accomodate my sons 2 seat go kart which weights about 500 lbs. I am going to install 5/4" thick x 6" wide deck boards perpendicular to the logs.
I started notching out one side of the ravine and I put down a bed of gravel and then used a tool to compact the gravel into the soil. I then plan to lay 4" thick x 16" long cement blocks on the gravel. I will lay the logs on top of the cement blocks.
My concern is whether this foundation will be ok. If any one log sinks, then it will throw off the structure. I could use some advice here.
Thanks.

BigD9 04-01-2011 07:50 PM

Wow, sounds like you will have some structure there. Hope you post pictures of what you are doing. I for one would love to see them.

My experience says with all the logs tied together using 5/4 boards this will insure all logs will settle together. If one log wants to go down for some reason, the load will be transfered to the other logs. Any reason for using 5/4 lumber and not 2x6 lumber? What kind of screws/bolts are you using?

As for the foundation, what is your bed of gravel resting on? Is there water flowing in this ravine? Where the logs will be sitting on the concrete blocks, at that point will there be a 2:1 or flatter slope to the bottom of the ravine? How stable are the ravine sides? Going have any kind of handrail or guardrail along the sides of the bridge?

Good luck and I'm looking forward to pictures.

Willie T 04-01-2011 08:31 PM

I wouldn't use blocks for the foundation ends, but rather solid lintel beams.. they already have rebar cast inside them and they are designed to carry these kinds of loads. Throw an 8' lintel across each end.

timrec 04-01-2011 08:44 PM

pictures so far..
 
4 Attachment(s)
Here are some pictures. The foundation is gravel on compacted soil. I then put a block on the gravel base. I am thinking about pouring some concrete instead of the gravel and then putting the concrete blocks on the concrete base...

Attachment 31511

Attachment 31512

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Attachment 31514

Ron6519 04-01-2011 11:43 PM

I'd dig 2 sonotubes(on each side) below the frostline and use Willie T's lintels to span them. I'd isolate the wood from the concrete using ice and water shield.
It won't last as long as pressure treated wood, though.
Ron

timrec 04-02-2011 06:33 AM

Quote:

Originally Posted by Willie T (Post 621540)
I wouldn't use blocks for the foundation ends, but rather solid lintel beams.. they already have rebar cast inside them and they are designed to carry these kinds of loads. Throw an 8' lintel across each end.


What is a lintel? Could you provide a picture or web link? I have never heard of a lintel beam.

thanks.

Ron6519 04-02-2011 08:05 AM

Quote:

Originally Posted by timrec (Post 621674)
What is a lintel? Could you provide a picture or web link? I have never heard of a lintel beam.

thanks.

Think of a concrete 6x6 with rebar in the middle.
Ron

dtsman 04-02-2011 10:46 AM

I would agree with digging 2 footers on both sides, and fill with concrete. Then pour a concrete header (lintel) from footer to footer, or use a wood beam from footer to footer, to lay the post on.

My reason, is not the frost line issue, but the vibration of the motor vehicles will cause the ends to settle faster than you will anticipate. Don't rely on the edge of the ravine for any support.

Your way will work, but will require maintence and regular inspection to keep them kids safe.


Bo

Remember,
If the women don't find you handsome,
they should at least find you handy.
(Red Green)


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