Large Scale Central

Trestle Design & Construction on the V&T

Seems like I need to splain the actual design. In short, the geometry was “set in stone” when I built the surrounding roadbed and mountain, both of which are (thick) concrete. Nine years ago I attempted the first version design, but just a couple weeks ago did a full redesign (to simplify things… long story, but the 1st version was whack job).

A week ago, I made a paper template showing what my new design “expected” from the existing conditions, because the roadbed forms were set out per the same CAD plan. I laid this template on the track, to ensure all lined up.

But tolerances are a b!tch, especially in this case of wonky concrete forms & etc. Nothing real matched my CAD-driven paper template. So I took measurements, marked the template up, corrected the template in CAD to match the conditions, re-cut the template and put it back out.

Here’s template attempt #4, which finally matched the conditions in where all the roadbeds are, and where all the bents should go. And how tall the bents need to be.

An experiment in photogrammetry, fwiw:

Now having a reliable geometry set, I reworked all the trestle design. Which will take a long time to build, because that’s how I roll (slow).

To my mind, installation is the tricky part, in conveying CAD-driven geometry back into the 3D site, for setting for piers. I imagine there are vastly simpler ways of doing it, but here’s my plan.

First, take out the track and the unnecessary 4x4 plywood supports, and put in temp blocks above the lower roadbeds.

I have a pier-pouring jig design in mind, very subject to further thought. Lasered scrap 1/8" plex, suspended via 3/4" pvc pipe from the existing plywood bridge. The point here is forcing the CAD geometry back to the site. It’ll require the BIG “hammer” [edit: I added quotes to “hammer” because Bruce’s comment made me] to get some concrete out of the way.

When that’s done, the remaining posts are removed, while the jigs are strapped to the plywood to hold it in place. Then come the remaining jigs for the 2nd set of piers.

In both pier steps, cement is poured through the upper holes of the jig boxes. The cement will reach down into the terrain, however it needs to. Upper pier surfaces are ground flat after the forms are removed.

And then Little Red Riding Hood said, “What nice teeth you have, grandma!” And mostly everyone lived happily ever after.

But back to my fairy tale, here’s the intended result.

Assuming all goes perfectly* with the bents and bent-assemblies, here’s how they will perfectly* go on the perfectly* cast piers.

*Re “perfect”: a relative term. Here used in the sense of being within 1 foot of the intended location.

Then the deck…

And the build jig (insulation foam with lasered cardstock templates):

And the eventual miracle:

So that’s my story.



Well, I DO have a MAUL…it’s SO much better (and bigger) than a hammer! :innocent:

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Thanks for that photo, Bob. Wow, evidence indeed.
As Rooster would say, Ho Lee Fluf! Or something like that…

Cliff, a big hammer will work … but … this will work much better :crazy_face:

Looks like you have a well enginnered plan for your trestle. Looking forward to seeing it come to life.

If you need any help, please let me know …

… I’ll get @Devon_Sinsley to come help you :upside_down_face:

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Haha! Thanks Dan. Stayed tuned, because around 20 years from now, I’ll be re-engineering it so I can finally install it from the wheelchair I’ll be using.

:grimacing: :stuck_out_tongue:

Cliff, I think I am on that schedule myself.

Nope. Now that you have let the cat out of the bag we’ll be asking “Is it done yet?” daily.

And I thought I over-engineered stuff! Jeeze! Looks great though.

This isn’t sounding like a good sign…

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I really don’t think that Cliff needs help with delaying this… :innocent:

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I think Cliff needs his own Department of Over-Engineering

Oooh, moving parts!
Yeah that’s the ticket…

My only complaint about the way folk build “curved” trestles (or any other bridge for that matter,) is that nothing in the construction of the bridge is curved except the rails.

A trestle has beams under the bridge ties that are straight from one trestle bent to the top of the next one.

So making a top surface out of curved plywood strip looks horrible - to me. Guess I am too picky.

I quietly say nothing but agree whole heartedly. I have several trestles that I need to build and they all are curved. I haven’t even begun making them yet but will make them as a series of straight sections with curved rails.

That’s why the plywood is the temporary bridge, which is getting replaced by the trestle.

Here’s the base jig design. Will use 1" insulation foam, lasered cardstock and some glue.

We don’t care what Rooster says and the history books have documented that over the years!
However bridge ties are different but there is always concrete decking !

I’m about to bag the handrails and refuges, since

  1. this is a non-prototype backstage bridge
  2. many prototype trestles lack them anyway
  3. they’re a pita to build on a curve
  4. they’ll easily bust off (especially with curved construction)

Idealism dies hard… But I’ll be able to go more proto on the other (straight) trestles, since they’re well documented for the V&T.


You could put some clear Lexon type of product on the outer side if you worried of stock falling off…

Thanks Sean, but I’m not worried about that. I’m just looking for ways to simplify, and reduce all the little pieces on the ground the following year. :slight_smile: