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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

L. Wakefield

QuoteDoes anyone have plans for mortice & tenon foot bridges, using curved logs???
 Ed
Now this sounds really Japanese- is that what you meant?  lw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

Jim_Rogers

Ed_K:
I could draw you one, if you want me to. I'd need to get a list of details off what you want.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Ed_K

 Jim, I'd be building the bridges diferent lengths. Depending on the length of tree and curve. As I'm logging I find trees marked to cut, that are to curved to sell as sawlogs, usually they are put into firewood. I am always looking for value added. My biggest default is not knowing how to join the bridge together, for strongest results.
 Thanks if you have some ideas. I'd like to try one to cross a small brook, 2' , to cross to my sugarhouse. Guess it would be 3' x 6'.
Ed
Ed K

Jim_Rogers

Ed_K:
I'll start thinking of a design and see what I can do with my cad program.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Don P

I think that's called a moon bridge, I worked for a guy that had 2 on his property that he'd built. He's kinda far out I'll try to make a reason to go by sometime soon and get a pic.

On the beam engineering, I did talk to a pretty knowledgeable oldtimer last night...this guy specced his first I beams at age 11 :o. He followed a verbal description of the beam calc and cautioned me about dynamic loading, which gave me an opening to ask about bridge design. I asked about a 4 ton rolling load, he said the rule of thumb is to double the load...the 2 point, point load. He said he would call it 9 tons to add a safety margin.  My present calc is for uniform load so it doesn't work for that...yet. Jim's program does have provision for that and I do have the formulas and a short cut to make the next calc.

Ed_K

 I like the moon bridge theory. If I can build them, thats what I'm going to sell them as  8).
 Thanks Jim and Don, I'll keep an eye here in hopes you can come up with something.
 New dumb ??? would eastern hemlock work for main beams?
 Ed
Ed K

Jim_Rogers

Ed_K:
Are you thinking about something like this?:


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

Ed_K

 Jim,
 Thats what I'm thinking of. Would like an upright in the center to tie railings to.
Ed K

Jim_Rogers

Ed_K
What is the diameter of the arc logs for your "Half Moon" bridge?
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Ed_K

Jim,
 Minium 6" on the tip end. Anything smaller will stay in the woods for fertilizer. I have a buyer for 5" tip 10', but they have to be dead straight. I see a lot of curved logs in a months time  :D.
Ed
Ed K

Jim_Rogers

Ed_K:
Now in Timber Framing if you want to make a pair of braces that will go somewhere in a frame opposite each other, you take one curved log and cut it down the middle or so, to make two "book matched" pieces of wood. That way you can have a brace on the right and a matching one on the left.
Ed, if you used this system with a little larger log so that each half was 6" across then you could have the stringers for the bridge.
If I was making a bridge I'd do it this way. I'd first cut the round log flat on one side as it laid on my sawmill table. With a little planning and a few blocks you could cut it just right to take a heavy slab cut off the butt end. And just skim a little of the tip of the log. Then flip it 180° and cut the other side flat, but as you are doing this plan for the total thickness so that you can easily divide what's left in two.
Then you'll have two arcs for the stringers.
I might before the two are separated turn the curve up so that both ends are up in the air and clamp it with a cut face against my log uprights. Then make one cut to flatten the two ends on the same plane.
If you did this and then cut the log in half you'd have two arcs with flat bottoms.
I'd attach a piece of pressure treated lumber, like a 2x8 or something like that to the flatten ends like this:



Now that you understand the principal of how you could cut two matching arc logs for stringers, here's what I came up with for a foot bridge.
Now you've got to understand that I didn't spend a lot of time making the arc logs in the cad program, I just made a straight one but you can see the idea:



So you have to envision that the ends of the side logs are on the green pressure treated lumber and that the railings and the logs are curved like you want them. The x's in the middle of the railing will have to be stretched to make up for the curve.
What do you think of my idea?
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

etat

Jim, I really like your idea.  Especially the input on how to get two pieces out of the same curved log so they match.  I need a bridge, for the upstairs of my house.  Seriously, it will connect two rooms and will be over the stairway.  It needs to be appx. 8 to 9 feet long and needs a rise in the middle of almost a foot.  It would be a problem for me to come up with such a log that would be suitable.  I feel that I could probably make what you describe if I did have suitable timber.  I am pretty determined, and usually accomplish what I set out to do.  With enough work, I feel that I could split such a timber with a ripping chain on a chainsaw.  I have already asked a few questions about such a chain on the chainsaw forum and I think this could be done.  Then everything could be neatened up and shaped with ax, hatchet, chisels, until the desired results were achieved.  This bridge would need to be safe for people, and occasionally the heavy object that would be toted across it.  What size would you recommend for the initial log, before being split and whittled down.  More importantly could a curved tree limb such as white or red or post oak.  I know of some trees with pretty big limbs but I've never heard of anybody milling a tree limb so I don't know if it would be structurally sound enough for the application.  The only other option I can think of would be to try to bend timbers to suit the application.  How about, say some 6/6 timbers, heavily supported on both sides with heavy weight in the middle covered with a tin frame with LOTs and LOTs of steam coming in.  My easiest option I can think of would be, either making a steel framed arched bridge, which I am perfectly capable of but don't want, or cutting and laminating enough plywood together and covering the edges with veneer, again, not my favorite idea.  I would really like to be able to accomplish this with solid timbers.I would really appreciate you taking the time to give me your thoughts on this subject.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Jim_Rogers

My first thoughts are "what is your building inspector going to want to see?"
Do you have one in your area?
You'll need to make it to satisfy him. If he needs blueprints for this 'bridge' you'll have to have a timber framing designer make one for you, and then have these drawing checked by a timber framing engineer.
I'm sure you don't want to hear all this stuff, but if you're going to make it you need to make it strong and right.
At the points of your house where these ends will attach, is this location strong enough to support for the new bridge?
If you build it without your building inspector getting involved and it fails your home owners insurance may not pay any medical bills for those who are injured.
It need to be build right for you, and the people who will own your house after you're gone (by selling and moving away) not by leaving this earth, but that too.
There is a lot to consider before you start the chain saw up.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

etat

Jim, those are VERY good questions, and I appreciate you asking before giving an off the wall answer.  I will try to answer your questions, and maybe give you more information than you want to know.  In  the county I live in there is no inspector, no permits required.  I don't always think this is a good thing because there is a fair amount of shoddy construction that goes on.  I am a roofer by trade, and my papa was a carpenter.  I wanted to build a house that will still be standing in a hundred years, without any noticeable sags or sways. Square, plumb, strong. The house is on a conventional foundation, 4 blocks high filled with concrete. Everything is bolted down.  All the work thus far has been done by myself, my wife, my kids, and guys who work for me.  The house sits on hard dirt.  The perimeter foundation is almost 3 feet deep, and two feet wide.  There are piers, dug the same depth underneath the house every 10 feet.  The floor joists are 2/12, 16 inches on center, and doubled in key stress points.  Sub floor is 3/4 plywood steady floor, glued and screwed.  The living room is 21 by 19 with a vaulted  ceiling, up, two beams, and flat up the center.  The beams are 10 inch I beams, with 2/10's bolted on each side of them, (there are two) and the framing fastened to that.  I used 3/4 oak cabinet plywood on the ceiling, lap cut and grooved to make it look more like boards, by hand.  This is fastened to laths, glued and screwed to the joists for the vaulted ceiling.  This plywood is fastened from the TOP side of the laths with screws, and glue.  All walls in the house are 2/4's doubled, or tripled, and sometimes even more in ALL key support areas.  l also made sure there were piers underneath all supporting walls.  All headers are 2/10's, with 2/4 nailed on top and bottom, and plywood sandwiched between the 2/10's.  The siding on the house is full 2/8 popular, that I cut lap joints into with a table saw and ran horizontally.  The outside walls consist of osb, house wrap, vertical 1/4's fastened to each stud, and then the siding fastened with 3 1/2 treated deck screws.  The outside windows and doors are all properly flashed, and trimmed out with pressure treated pine.  The poplar has been treated for rot, and waterproofed, front and back.  I have spent a TON, on extra lumber in framing, but was able to do so since We are doing the work our selfs.  The roof line is multi pitch, part is 17/12, that is over the upstairs rooms, part is 10/12, over about half the house, there is one false gable on the front. There is a full front porch, and half back porch these are 4/12, Only slightly less deep foundation,   The porch floor is pressure treated, floor board, and joists. Each joist is stripped across the top with strips of tar paper, before decking.  The house consists of appx. 22 hundred square feet heated.The ceiling on the porches is tongue and groove.  The area for the bridge, I am confident that I could run railroad iron across, and stack a pallet of shingles on it.  I could easily tie the bridge in to the joists, through the floor.  I want this bridge to be strong.  NO deflection, NO chance of ever collapsing.  At least for the next hundred years. I would rather use square timbers for the arch rather than rounded.  The rails and balusters will be like for the stairs, and no further apart than 4 inches for safety.  I'm trying to cross all my i's and dot all my t's, even to the point of extreme.  I appreciate your help and suggestions.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Jim_Rogers

cktate:
Well it sounds like you've dotted your i's and crossed your T's alright.
It always helps to know all the facts, and I know them now.
You've said it has to be 8 or 9' long but you didn't say how wide?
Also, you mentioned you'd like to work with square timbers, that OK, too.
Can the timbers go across straight and make the deck rise the foot you need?
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Bro. Noble

Seems as though PaulH made some arched beams a while back.  Maybe he'll post some pictures and tell us how he did it.
milking and logging and sawing and milking

etat

Jim the bridge needs to be appx. 4 feet wide.  The actual opening it needs to cross is appx. 5 feet.  Wanting to make it longer so as to have a more gentle rise. The timbers HAVE to have a arch, can't be straight because I need the head room underneath.  I absolutely need to gain about 10 inches underneath. Plan B, if I can't make the arch would be to go up a couple of steps on each side, and run the timbers straight across even with the TOP of these steps.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Paul_H


 
Noble,
This is the arch beam we made last year.It is about 16' from end to end,and I was told it was a 21' radius.

We laid the log down on the Mobile Dimension and blocked it up so it was fairly level.Then we sawed it with the horizontal edger until it was a flat plane.Afterward we took it off of the mill and set the Alaska mill at around 14" and milled it again leaving a 14"  two sided beam,and a nice thick curved slab underneath.

It would have been simple enough to pull two 8" beams (with a bit of wane) out of it instead of the one 14".I thought that maybe a beam saw attachment for a chainsaw would help square of the curved sides,but haven't tried anything like that yet.

If we ever had to do another one with out the MD,the plan was to lay 1 1/4" black plastic pipe along the log length,parallel to each other and fastened on to the log in such a way to guide the first cut with the Alaskan mill,instead of the usual "ladder".

I hope this helps.
Science isn't meant to be trusted it's to be tested

etat

Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Ed_K

 Thanks Jim,
 Should I put anything between the floor & beams? Like CK did with the tar paper???
 I like the beam, Paul H. What kind of tree was it?
Ed
Ed K

Paul_H

Thanks.
It was a Douglas Fir,and it was in the firewood pile.It's still sitting under cover in the yard.
Science isn't meant to be trusted it's to be tested

Paul_H



I just grabbed the kids crayons to show how my cousin built an arch bridge over my Dad's pond several years ago.

The bridge was made of 2x10  's cut at angles and glued and screwed in four layers for each stringer.Much like building a header,or a long laminated beam,only cut to make the curve.

The span is at least 20' across and sits on concrete pads like the ones in the drawing.The idea being that the the more pressure bearing down on the bridge,the more sideways pressure on the footings.

A good strong arch.
Science isn't meant to be trusted it's to be tested

Norm

Boy now you guys have me looking for curved logs instead of straight ones. I sure like the ideas in this thread.

Sure Paul the kids crayons, I'll bet you got the big box with the built in sharpener just like mine. :D  

Jim_Rogers

Ed_K:
I've heard of doing that on decking before, sounds like a good plan to me.

Square rule joinery is a method of laying out joints from a reference side and corner. All joints are draw so many inches off this side/corner, similar to doing it from center lines, but is somewhat easier because you don't have to make the center line and the framing square rests against the face of the timber. Using square rule joinery you don't have to worry about the inaccurate timber as all joints are drawn to a envisioned inner timber.
I'll have to do a demo at the next workshop and take some pictures and write up a story about it.

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

Jim_Rogers

cktate:
I'd go for plan B and make it easy for yourself. That way you don't have to deal with trying to make two or three curved beams that match.
I say three as you might need a center support as well as two outside stringers.
Think about this idea for a while.

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

Jim_Rogers

One of my timber framing teachers has used a chain saw mill to shape curved logs before. He cut a very thin board to bent over the curved log so that the mill could follow this gentle curve and cut the log to the same gentle curve. It works very well to make the curved sides smooth.

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

Jim_Rogers

Paul_H:
I'm reading a book about timber framing and the current chapter is about covered bridges.
The author has sited that the point where most bridges fail is where the wood meets the concrete or stone work. The problem is that the rain water collects there and causes the wood to rot. Hopefully your cousin has taken care of the in your Dad's bridge. If he hasn't you should look at this area during or after the next rain storm and see if the water is collecting there.
Jim Rogers
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

Paul_H

Jim,
I phoned my dad this morning to ask about the bridge.He said it was put in around 1980.About 3 years ago,him and his brother Thor replaced 6' of rotted wood on either end with treated wood.
I wonder if it would have helped to slightly slope the concrete footings and use treated plywood as a shim?

Norm,
I'm happy if I can find a pen around this place ;)
Science isn't meant to be trusted it's to be tested

Ed_K

 Jim, do you do private workshops, or teach at a school? I remember a timberframing school here in Ma, but don't remember the name  :-[. HeartWood? :-/
Ed
Ed K

Don P

CK,
In your case I think the bridge is looked at as a ramp. The max rise would be 1:8...you need 14' to come up and back down 10" Plus the timber thickness :-/. Steeper than that and they like a step, course you could do the step or 2 then arch.

etat

Don, I think that's the best feasible way to go.  Couple of steps and slight arch.  angle iron underneath the steps, and lag bolts through the floor and joists.  I went out to the house after your post and roughly mocked the idea up with scrap 2/4s.  Also this way I can get the actual arched timbers down to about 6 feet long, Probably much easier to come up with.  What I do have on hand, is some full 8/8 yellow poplar beams, 10 feet long, boxed heart.  The ends of these are sealed, but there is some checking, nothing really serious.  These have been air drying since June.  One thing I'm wondering is if I put these in a open shed side by side and supported on both ends on concrete blocks, and Stacked a LOT of weight on them , this I could easily do with bundles of shingles, if they would bow naturally enough to get some arch.  I could let them sit until spring as since mother fell I now have a temporary bridge across the gap.  Only thing is you have to remember to duck yer head.  This I can live with for a while.  Another crazy thought would be to stack em high enough that you could get a couple of large wash pots with burners underneath them and let them steam, for a Long time.  I've never heard of anyone steaming lumber of this size.  If anyone thinks this is even remotely feasible do you think it would be better to go with a different type lumber such as oak or pine etc.  How about some green lumber supported and weighted? With a couple of steps the rise would only need to be enough to give it a little character.   Laminating 2/10's or 2/12's as described so a slight arch can be cut into them also sounds like a pretty good idea.  I don't know though, I just like the sound of solid beams.  Maybe if I were careful enough choosing, gluing, laminating, and cutting they would appear to be solid.  I'm starting to get the idea in my head what the finished product needs to be, and how I want it too look.  As I said, I'm pretty determined.  I mortise and tenoned all the exposed beams holding up my porches.  With a skillsaw, sawsall, chainsaw, drill, and chisel, and I had never done anything like that before.  With conventional fasteners and metal plates I could have put them up in a day, or less.  Wound up spending a week on them.  I've been trying to work a little craftsmanship into the design and look of the house and not only had it been a learning experience for me, it's been a lot of fun (and headache too).  I guess I'm saying I don't want this to look like something just throwed together with the easiest available materials.  We've waited a LONG time to build this house.  Want it to be part of our legacy.
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

etat

Oh, and don, I just realized you're probably right about it being a ramp.  But please, don't tell a :nyone else, I want to call it a bridge. :) :) :)
Old Age and Treachery will outperform Youth and Inexperence. The thing is, getting older is starting to be painful.

Don P

 :D :D A rose by any other name ;D...just kinda dawned on me the residential code doesn't address bridges but it does ramps, you have to think where they would bury stuff in the book sometimes. Come to think of it one of the moon bridges I mentioned did have cleats nailed to it, the deck had a pretty heavy arch and was slippery when wet.
My guess is you'll never bend something that large, I've got a locust beam under a stack of wood trying to flatten it...9 years under an 8' stack and its still lookin like firewood. What about ripping into 1X drying and planing, then epoxying to a curved form? You could number the pieces to reassemble in order. In one of Tedd Benson's books, Norm Abrams describes a timber for his house being made this way. There are some glulams using fiberglass in the laminations to increase strength also.
You can rip a groove into what will be the top edge of the poplar timber to help the check form there, it will then be covered by the deck.

Jim_Rogers

Paul_H:
The book I just finished had a chapter about covered bridges and they say that they put some wood in near the stonework and/or concrete work to be a cushion between the bridge truss timbers and the stone/concrete area. This other wood is there to protect the truss work and if it rots in 20 or 40 years they jack up the bridge and put in some more to replace it. That way the bridge truss system doesn't rot and therefore make the bridge fail.
So a treated plywood shim would seam to be the correct way to go.

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

Jim_Rogers

Ed_K:
I teach timber framing here in my sawmill yard. We're cutting out a frame for a small barn/cabin/shed.
I'm located in Eastern Ma, and Heartwood School is in Western Ma. A very good school, and the guild holds many classes there also.

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

L. Wakefield

   OK, this is a cheat- but look at www.gardenbridges.com. Not CAD, but photos. A little math and you have your parts dimensions. See one, do one.

   I think you're having more fun with crayons, tho.

   I'm still scratching my head over the MD post. Can't figger out if the log was curved to start or not. I'll have to read it again.  lw
L. Wakefield, owner and operator of the beastly truck Heretik, that refuses to stay between the lines when parking

L. Wakefield

   Oh yeah, I was just thinking as I read the part about steaming the LARGE beams. There was a thread or 2 awhile back about trees that grew under stress would bend naturally as you cut them- it was a thread predicting which WAY they'd bend. Not starting with bent stuff but ending up with it by mistake. Could you take advantage of that or is the curve not enough?
  
   I think Tom had a bit to do with that thread IIRC- it was a long time ago, shortly before or after the first mention of a barber chair type hazard.  

   ps- I figured out the MD thread by looking at the grain. That one was curved to start and you were describing how to cut flat faces, right? It looks WAY rugged for this application.

   This all reminds me of the calculations my x-husband did for the beams for the underground house- the lateral forces and torque that would come with loading the arch. He musta had something 'on the beam' (so to speak)- it hasn't fallen down (yet).

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

Paul_H

LW,
Yes,you're right about the log being curved before it was milled on the MD.The hardest part was getting it to lay flat for the initial cuts.

And you were right about the "fun with crayons" too :D

I call it my DAD program.
Science isn't meant to be trusted it's to be tested

Jim_Rogers

DAD program! LOL  :D :D :D :D :D :D
Whatever you do, have fun doing it!
Woodmizer 1994 LT30HDG24 with 6' Bed Extension

james

 arch bridge presses out at the ends as it trys to straighten out under load  The ends need to be 2 to 3 times the weight of the bridge plus the max load that will ever be on it or they will move   not a good thing if they are aginst the top of a wall in a house: for safty have the plan for the bridge checked out by a structural engineer who is familiar with arched bridges :o

james

oops ment the supports under the ends need to be heavy  or the bridge trying to straighten out will push them and the walls they are sitting on out away from the area the bridge is spanning :P

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