[KarlK]

Hey I'm seeing thoughtful responses on the strength from some of my favorite NW Hikers types. This prompts me to mention one of the reasons I like trail and saw work so much: I get to work with very smart and interesting people and I get to learn a lot by doing so. I've found the same to be true in the wildland firefighting realm, and very true as well in working with Team Rubicon in disaster responses and mitigation ops. TR is a vetran's led 501c(3) comprised mostly of military vets, former / current first responders, and regular civvies. TR provided me the path to get into WLFF and provided first rate chainsaw training as well. And a bunch of new friends. Highly recommend checking out Team Rubicon. https://teamrubiconusa.org/

[KarlK]

One last clarification made in relation to Sculpin's comment: the shallow arch would add strength to downward force if the ends were pinned, otherwise the load vectors get, in the words of we retired physiologists, "wonky".

[Bowregard]

Thanks for the specs KarlK. That will make interesting reading over the Winter. There was a question asked earlier by fourteen410 that I think got lost in the Design discussion:

[Now I Fly]

Thank you for the great work, and for posting this report! Well done!

[neek]

In addition to being both cool and useful, this could save lives. Well done. Can't wait to check it out.

[Carbonj]

I worked on trail crew for almost 35 years. Yellow cedar,red cedar, and doug fir in that order,were desired for rot resistance and longevity. We would generally use whats nearby on the ground, unless we flew it in, which can be a huge paperwork hassle. True firs and hemlock have a short life span. Putting in footlogs in glacier river you take what you can, but red cedar is the lightest, and when you have 50-60 ft crossings and no standing trees around for rigging light is right, also on the carbon, mowich, and west fork of the white river you can get multiple washouts in a season. One summer we replaced the south mowich 9 times. Also when the log has a curve you place it with the curve down. When a new crew placed a bridge with a pronounced curve up in we took to calling it the hobbit bridge and took bets to how long it would stay upright.

[Stefan]

I feel like I am watching a bridge builders geek club now.

[Sculpin]

[Kim Brown]

[Kim Brown]

Loving the discussion here. Most is over my head, but I like it anyway. If I could do it all over again I'd be either a musician or an engineer. Or an eccentric rich person. But all I know about engineering is what I see on Bugs Bunny cartoons. In my right-brained mind, seems that if a load were at the top of the arch, the weight is distributed to each side of the arch; once the energy meets resistance at each end, it stacks up and creates a stronger support overall. The arch itself is the distributor of energy. Am I correct? (Seems that's about what KarlK says, with perhaps some added cartoonic nonsense)

[KarlK]

In reply to fourteen410's question about what makes a good donor tree here's how this worked: The Other Mike and Joe Hofbeck (both retired engineers with abundant backcountry bridge-building experience) evaluated options that were pragmatically close to the bridge site in 2021. A nice spec-worthy Doug fir was identified on the N side of Eureka Creek (healty, sufficient diameter and length). Landon Decker (MVRD Trails Manager) OK'd the selection, and he and one of his crew members expertly felled the tree on Oct 12, 2021, dropping it between two potentially tree-busting rock features to prevent breakage.

Landon chopping the face cut

Landon and Collin sawing the backcut

There it goes!

Peeled -- A teriffic log! Note placement between rocks

[Brushbuffalo]

Karl, two minor questions not yet brought into this fascinating thread: 1)how many ripping chains did you go through on your big Stihl? 2)Did one of you locate some blocks of ABS and manufacture the shims to fit? Fantastic project. I may never get back there again, but many future wilderness wanderers will have much easier and safer access to a rough and scenic area, thanks to your collective dedication and sweat.

[KarlK]

Brushbuffalo -- The Other Mike did the chainsaw milling with his 460 and did not indicate the number of ripping chains involved. But me did mention that the job wore out the guide bar groove. 32 inch guide bars are pricey! Mike also indicated that the hardware he donated to the project equated to $300 of out-of-pocket expenses. As you know (perhaps all too well) volunteers often spend a lot of $$$. I think that one of the reasons trail vols tend to be older folks is that we old guys and gals have all the money! Joe H and Steve G made the ABS shims.

Chainsaw chains in various states of health

[KarlK]

Dear Sculpin -- Yep, I had a convo with Joe H the morning and he said what you said. All readers of this discussion are now eligible for the Joe and Karl Certificate of Backcountry Bridge Engineering. It's delivered free, in imaginary form, and has a tasteful imaginary gold trim. Possession of the JAKCBBE makes the possessee eligible to help with trail and bridge projects.

[Sculpin]