Need to make a log bridge.

[L. Wakefield]

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

Now this sounds really Japanese- is that what you meant?  lw

[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

[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

[Jim_Rogers]

Ed_K:
I'll start thinking of a design and see what I can do with my cad program.
Jim Rogers

[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 . 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

[Jim_Rogers]

Ed_K:
Are you thinking about something like this?:

[Ed_K]

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

[Jim_Rogers]

Ed_K
What is the diameter of the arc logs for your "Half Moon" bridge?
Jim Rogers

[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

[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

[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.

[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

[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.

[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

[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.

[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.

[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.

[etat]

WOW!!!!!!!!!!!!!!!

[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

[Paul_H]

Thanks.
It was a Douglas Fir,and it was in the firewood pile.It's still sitting under cover in the yard.

[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.

[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

[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