Need to make a log bridge.

[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.

[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

[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 ;)

[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

[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.

[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.

[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

[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

[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]

   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

[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.

[Jim_Rogers]

DAD program!  :D :D :D :D :D :D

[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

[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