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Need to make a log bridge.

Started by Viking, November 25, 2003, 09:37:18 AM

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Viking

it only has to be about 10-15ft long and about 3ft high. About 3-4tons max load. I have pine"every type" birch, poplar and cedar. which would be most suitable for the job ? all tress are 16"+

Scott

Don't use poplar or birch. They rot way too fast.

Jim_Rogers

What type of bridge is it?
A logging trail bridge for a skidder?
A trail bridge for snowmobiles?
A bridge for cars and pickups to use in a driveway?
Are you going to use the logs in the round or are you going to have them milled into timbers?
We'd need some more information in order to give you some help.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Viking

it will be used for a 4x4 3/4 ton or 1 ton pickup truck to drive over, and the logs will be round, but i can shape them with a chainsaw.

the bottom of the creek "in the area im putting the bridge" is cap rock, so i can put supports directly in the middle. i just dont want to not use a bridge and dammage the two edges of the creek.

Jim_Rogers

Are you going to lay the logs across the water and then put a deck on it for the 4x4's and pickup?
How wide will this bridge be?
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Viking

8ft wide should be more than enough since it wont be for a dully. im to sure about the other part yet.

woodmills1

I have a NH or federal publication on making bridges using 2x stock laid on end.  I can try to find it if you want.  Always intested me to build bridges but never did one yet.
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

Viking


L. Wakefield

QuoteI have a NH or federal publication on making bridges using 2x stock laid on end.  I can try to find it if you want.  Always intested me to build bridges but never did one yet.

   I wouldn't mind seeing that one either. I wonder if they have it on line?  lw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

woodmills1

It is called User Friendly Guide to Timber Bridges.  Put out by the university of NH cooperative extension.
http://ceinfo.unh.edu/fgen1043.pdf
James Mills,Lovely wife,collect old tools,vacuuming fool,36 bdft/hr,oak paper cutter,ebonic yooper rapper nauga seller, Blue Ox? its not fast, 2 cat family, LT70,edger, 375 bd ft/hr, we like Bob,free heat,no oil 12 years,big splitter, baked stuffed lobster, still cuttin the logs dere IAM

OneWithWood

Hey, thanks Woodmills!
I too am interested in bridging some of the streams on my property.  I had not seen this pub before.  It will make for some good reading  :P
One With Wood
LT40HDG25, Woodmizer DH4000 Kiln

Viking


L. Wakefield

   Totally excellent! Thank you for the reference. I have saved it and will print it out as time and paper allows. I had not realized that historically they had made arched timber bridges, having only seen the steel ones.  lw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

Jim_Rogers

I've been thinking about your idea about making a log bridge.
I drew up an idea I had about how to do it.
First I did some math and figured out how strong or how big the logs needed to be in order to support the weight of 8000 lbs. And came up with 16" logs 16' long cut flat on the top by 2" for the decking. These stringers, as they should be called, are 16' long and are supported mid span with a stack of three logs that are 8' long and flattened on two side, the top and bottom.
Place the three 8' logs in the middle of the span and put the (5)16' logs over them. Then attach the decking which should be 4"x10"x8' or wider than 10" if you can but not any narrower.
Add side rails if you choose.
 
Here are some drawings of my idea:







You can see that the stack in the middle holding up the long ones might need some 2x4 or something to hold them straight up and down, ( I didn't draw them in).

And you'll have to find some very long and strong nails to nail the decking down to the logs.
If choose to build something like this you could leave the bottom of the long stringer logs round, and flatten only where they meet the supporting 8' logs, but don't make them any thinner than 12" and it should carry the weight of 8000 lbs.

What do you think of this design?

Jim Rogers

Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Kevin

I made one of those --Photos MUST be in the Forestry Forum gallery!!!!!--.com/photo/13012199/14138748NVHXEuTUrM]Bridge Link[/url]

Viking

Jim_Rogers, wow, thats pretty nice, can i ask which program you used to make the drawing ? and may I use your idea / its great and it dosent really restrict the water flow.

Jim_Rogers

I made that drawing with my timber framing cad program.
After reviewing my figures, I think you need to make the center support only two logs high and then the third log, which will make the bottom of the deck 3' off the floor of the stream bed.
Also the stringers need to be 14" from cut face to cut face not 12". But as mentioned the cut face only has to be where the stringers rest on the support logs.
I'm concerned about the support logs shifting as you drive over the bridge so I'd nail some 2x stock vertically to the sides of them to make the stay stacked up and be sure to secure them to the stringers so that when you drive onto the bridge the bridge won't shift and push the stringers sideways away from the vehicle.
You might need to put in some diagonal braces between the stringers and the support logs.
And you can use the design if you choose.
Make sure you use straight and strong logs.
The math I did was for eastern white pine, in all the pieces.
I spaced the logs so that there is one in the middle and the one either side is 2' on center. The outside logs are flush with the ends of the 8' support logs. This way they are directly under where the wheels of the pickup truck will be rolling over the deck, giving it the most support.
If you can use wider support deck boards it would be better, but a full 4" x 10" should support one quarter of the weight of a 8000 lbs load at that span.
Good luck with your project and take some photo of the finished bridge when you've got it done.
Jim
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

etat

I've helped my grandpa, my dad, and one of my uncles build bridges before.  They never really had a plan I could see, just tried to cut some white oak logs, big as they and the horses could snake across, streched two on each side under the wheels, and then two or three spaced out down the middle.  Then floored em with rough cut 2/  white oak.  They just always seemed to know when they had it good enough.  I remember startin the spikes with a regular hammer, and then havin to drive em on down with a heavy blacksmith type hammer.  Havn't been in them woods where the bridges was in years.  Now I'm a wondering if there's anything left of them.  I know horses shore didn't like walkin across them wood bridges!  Had one jump off one one time into some ICY cold water  with me on him.  Best I remember I was about 16.  There was a corn field across the bottom and somebody cranked up a corn picker.  I like to froze before I got back to the house.  Wasn't the horses fault, scared me too so I never held it against him.Oh, and they tried to nail the nails where the tires on a tractor or truck wouldn't run right over them, because them nails WILL back up occasionally.  
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

etat

Also, don't put supports in the middle, if the creek floods those supports will catch every tree limb that comes by.  Then if it builds up enough pressure, it'll take your bridge down stream.  You do want to anchor good to each side of the bank also.  Even if it doesn't flood those supports will soon catch enough stuff to dam water.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

etat

I know you're probably gettin tired of me but I thought of one more thing.  After the sideways planks are laid on the bridge lay some planks 'lengthways' where the tires are goin to be runnin on the.  This will help distribute the weight of the vehicle across the whole bridge.  We sunk our pilins on each side of the bank, diggin it out with post hole diggers.  The ends of the lengthwise logs spanning the creek started up on the bank, dug in so as to level off, and then crossed the pilins which had a sideways log mounted on top of them.  Everything was dug and chopped out by hand, other than the top floorboards.  Best I remember it would take appx. 3 people and a couple of horses about a week per bridge, not a small undertaking, but a lot of fun.  Yall done brought back some good memories for me and sorry if I'm speaking out of turn here.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Jim_Rogers

cktate:
Your comments are always welcome. Experience is the best teacher.
Viking will have to address the center support section as to whether or not there is a chance for wash out or collecting debris.
Viking: I've been cautioned that a moving load puts more stress on a structure than a stationary load, so my sizes my be way off. You should have someone with more engineering experience check the design you choose for your intended loads.
Good luck.
Jim Rogers

ps. I agree with the double planking idea, spreads out the weight over more timbers.
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Viking

ok i know someone who builds bridges in CAD software also, ill just get him to go over the numbers too, i just asked here cause sometimes he isnt so easy to get a hold of.

etat

Thanks, Jim, I was afraid my post jest didn't sound right, jumpin in and all like that. I've got a couple of cattle gaps over creeks, and I usually have to check them after each rain.  If they catch a log, more trash and debri will start catching behind it.  You wouldn't believe the brush and debri that caught on them tires.  Was a bugger to untangle and clean up.  I don't know if there is water flowin in the ditch for the bridge or not.  But not only will a support in the middle of it tend to catch stuff, or if it is dry let grass and weeds grown up around and if it does rain  it could make the water start swerving around it, and thus start deteorating the bank. On another note, and this is a true story.  A friend of mine had a big cornfield and about 15 years ago somebody started comin in at night and stealing his corn.  Now his old pole bridge was gettin pretty ratty.  One evening we went out to that bridge and hooked a couple of log chains to it.  A couple nights later he told me he heard em come in and he slipped in there with his four wheel drive and jerked that ole bridge off of that creek.  Now this was a man who would have given anybody a mess of corn, but he didn't like stealing.  Not a big bridge, just about 10 or 12 feet across, and not that deep.  When those varmits come out, they run the front of their truck of in that little creek.  Might a been because he slipped in behind them on the other side and fired a warnin shot or two in the air. He then went out with a tractor and pulled them embaressed kids out, and gave em the corn they had stole. Wouldn't let em give it back  But not without lettin them listen to an hour or two of his preachin!  I recon after that they never come back.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Ed_K

 Does anyone have plans for mortice & tenon foot bridges, using curved logs???
 Ed
Ed K

L. Wakefield

   I saw this as a picture at the beginning of the forum and thought it was a REALLY WEIRD table. It all makes sense now!   lw

QuoteI've been thinking about your idea about making a log bridge.
I drew up an idea I had about how to do it.
First I did some math and figured out how strong or how big the logs needed to be in order to support the weight of 8000 lbs. And came up with 16" logs 16' long cut flat on the top by 2" for the decking. These stringers, as they should be called, are 16' long and are supported mid span with a stack of three logs that are 8' long and flattened on two side, the top and bottom.
Place the three 8' logs in the middle of the span and put the (5)16' logs over them. Then attach the decking which should be 4"x10"x8' or wider than 10" if you can but not any narrower.
Add side rails if you choose.
 
Here are some drawings of my idea:







You can see that the stack in the middle holding up the long ones might need some 2x4 or something to hold them straight up and down, ( I didn't draw them in).

And you'll have to find some very long and strong nails to nail the decking down to the logs.
If choose to build something like this you could leave the bottom of the long stringer logs round, and flatten only where they meet the supporting 8' logs, but don't make them any thinner than 12" and it should carry the weight of 8000 lbs.

What do you think of this design?

Jim Rogers

L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

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