How about a stone or concrete viaduct, like Starucca. You could fabricate it out of plywood. There is actually another set of tracks that run through the arches on the other bank.
Oh, I'm not worried at all about the 2x8's strength. I was just saying that would be the bottom of the bridge. Now that I think about it, I'm gonna tear up my basement for a few years to build this!!! Well, it'll be worth it.
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Sure it's a feasable option, if I had the room. 12' x 12' is jaut about my limit. I'm trying to cram a fair amount of running space, with a small engine yard up top, while staging yards are about a foot below.
As for the 2x8, I think that would be amply stiff. (The main concern here is deflection, not strength.) If you would like to calculate the deflection yourself for various beams, here is how to do it:
D = W*L^3/(6000000*psi*H^3*B)
W is the load, at the center of the beam, in pounds. L is the beam length; H is the beam's thickness; and B is the beam's width, all in inches. D is the deflection at the center, in inches. Exponentiation is denoted by ^. I assume a Young's modulus of 1500000 psi, which is typical for structural lumber.
For lumber, a nominal dimension of 1 inch is .75 inch, 2 inches is 1.5 inches, 4 inches is 3.5 inches, 6 inches is 5.5 inches, 8 inches is 7.25 inches, and 10 inches is 9.25 inches. So your 2x8 is actually 1.5x7.25. Plugging all that into the formula, along with a length of 13'8 or 164 inches, gives a deflection of .03 inches per pound, or about 1/32 inch.
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What about the feasability of modifying the track plan and incorparating a single helix, inside a mountain that would connect to all three levels ? However that would also require the addition of reverse loops on each level.
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First of all, thanks for the quick response. Secondly, I plan on using either O48 or O60 curvers, so I can run AC4400CW or 4-8-4 Northerns somewhat realistically. I may have accidentily made a mistake on my calculations, because now your 13'8" seems correct for O27. I now think it will be around 12' since it will be my middle level, which sticks out a fair amount. That actually helps, if I have to dismantle and move the layout.
Thanks again.
-Scott
Even with O27 approaches, I don't see how you can get a bridge longer than 13'8 onto that layout.
Hi there.
I am in the process of building a 12' x 12' O scale layout. I have mountains on the way, but I plan on having lower, middle, and top track levels (all connected by grades in the back, out of view) but the middle level is going to connect kitty-corner (basically, across the entire layout). I was thinking of modeling the Helgate Bridge, but any bridge with work (except wooden trestle). I have worked out the calculations, and it ends up being around 15'6" or so. I was planning on building it in 2 parts, for easier transportation. I was thinking about a 2x8 as an under-support (two-track mainline).
Any revisions, ideas, questions or coments would be greatly appreciated!!!
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