Large Scale Central

Too bent to bother? (trestle question)

Track and Trestles
#1

OK, here is the deal. I have a spot where two tracks enter two tunnels, one of which is directly over the other. This is O scale and the height differential is 24" or so (scale nearly 100 feet.) The upper track approaches the tunnel on a curve on a trestle that runs right up to the nearly vertical face of a rock wall. The lower track approaches its tunnel in a sharper radius curve on the ground.

What I would like to do is take the middle of the trestle out and replace it with a deck bridge, but return it to a couple of trestle bents before it plunges into the tunnel. The lower track can align itself to its tunnel running in under the deck bridge. I would like to design two bents which the lower track can split as it enters its tunnel.

There is really no choice in changing the verticality or the position of the rock wall and both tracks are coming off of lift out sections that are locked into the corner of the room.

What I want is a practical bent design and not a suggestion to throw out the track plan if you please. I searched Google images but my Google-Foo failed me.

Any ideas?

Thanks

Charley

#2

a pic of the situation may help visualize what you are doing and how the bents need to work. Some prototypes go to a lower bridge like section to span obstacles

#3

Can you post a picture of what you have now? I’m visual and need to see things to figure out. Also, on the bents - do you want them steal or timber?

#4

Most railroads would have installed a bridge section, mounted on a couple of lower/shorter trestle bents designed to carry the weight of the bridge over the lower tracks…

Like they say, a picture would be better…

#5

Can’t upload a photo to save my life. It’s on my desktop, it’s in photobucket. Looked around for “how to upload photos” and struck out. Suggestions

New photo album called “trestle” with one photo. What I want is two bents much higher (and broader) with clearance where the red rectangle is (at the bottom) so that I can run a track through the bottom of the two bents, in line with the upper level track.

Sorry about not being able to post pictures.

Charley

(http://freightsheds.largescalecentral.com/users/ccsii/photos/Trestle.jpg)

OK I got it!! here is the picture ^ it’s a wooden trestle.

So obviously the weight being born by the center legs needs to be transferred to the outside legs and they may need to be doubled?

#6

OK that explains it a bit better.Since you only have two of these you need to go through this way, I would think of making two pieces of pony truss too span the truss from side to side to support the bent. Basically a pony truss bridge over the lower track that the upper bents set on.

#7

Looking at it from a technical standpoint, if you want it to plausible in the real world, it will be difficult to design.

Think of the two verticle posts carrying a majority of the weight of the train. You will have to have a major structure to hold the weight.

#8

Lose the two vertical members in the middle of these bents. They absolutely must go bye-bye.

Build a pair of rectangular bridge supports either side of the lower track. These supports should be high enough to give your lower track vertical clearance.

Straddle them with a freelance tall wooden trestle-like structure which spreads all its weight over these side structures.

This can be done either by building the upper structure rectangular, with all the vertical members resting on the side structures, or you can have a trestle bent, if you insist, but with the center posts angled out to rest on the side structures and not above the lower track.

This upper structure, which I gather is supporting a curved track, should have much more substantial diagonal and X bracing than it would have if the track were merely straight, as side forces would be substantial. It would be realistic to camber the structure somewhat from uotside the curve.

On John Allen’s original Gorre and Daphetid RR there was a bridge supported by the kind of wooden structures I am talking about. The lower track ran to his original turntable location, in the right center of his pike.

#9

You don’t need to throw out the track plan; it only needs a bit of modification.

:wink: :slight_smile:

BTW I have seen pictures where a guy built something like that on an European layout. It looks mighty peculiar to anyone who has just a bit of engineering background.

#10

In such a case the railroad would probably go from wooden trestle to a steel deck bridge and steel trestle (viaduct) as the supporting structure could be more spindly and still have good strength. Also greater strength would be needed to sustain stresses on a curve. The deck structures would be several straight segments with only the track curved on top.

#11

I was thinking along the same lines as Richard, the curved track on a straight truss. I have one on the NMNRR.

(http://i1234.photobucket.com/albums/ff403/dave2-8-0/BRG-26.jpg)

Only for your use it would start at the tunnel portal.

#12

Thanks all, I think I know which way I am going with this. It may be a while but I will post pictures (now that I know how!)

Charley

#13

Ok I came up with a quick design, hopefully this helps.

img[img]

I’ll explain what I have here. I dont know if this is an ideal situation, but you already know that.

The Green polygons would be large beams for the upper trestle bents to sit on. In real life we are probably talking 6 x 16 s or something like that. I have not drawn in all the beams because I didnt want the drawing to be too cluttered.

The white bents have a lower stage and an upper stage. The lower stage is built similar to a wood tunnel support. You can see the angle at the corners to strengthen the joint between the vertical and horizontal connection. The upper stage is built like a standard wood trestle bent.

The magenta bents are sub-supports. It would seem to me you would need extra support for the upper track and thus the need for sub supports between the primary supports.

I dont know if this is really sound, structure wise. But it would work in a modeling world. And it does have the appearance of proper engineering.

#14

Well, Jake, I’m not sure that if I were an engineer I would approve of that, but hey, it’s your railroad! The magenta bents, that you have called sub supports, merely sitting on beams, regardless of their size, are a serious problem, and would never get approval, except perhaps in a Bangladesh clothing factory, and then the owner would get arrested…

If it were me, I’d prolly build a couple of stone arches over the lower track to act as bridge supports, and run bridges between them to the tunnel.

Attractive as we may find them, I really don’t think trestle-style structures are the correct thing here. Trestles were most often used over dry gulches, or the dry part of river crossings, and later these locations would be filled in by the railroad with material from a nearby cut until the trestle was partly or completely buried, thus the trestle over time would be converted to fill. There are many large railroad fills in existence today that conceal complete trestles buried within them!

Clearly, completing that kind of earthwork would not be the intention of your railroad in the location described to us here.

#15

It would sure be nice if we could see a track plan, even a rudimentary one.

That said, let me see if I understand what Charlie wants…

He has two curves approaching a cliff face with tunnels, one over the other, separated by 24 vertical inches, with the lower curve being on a sharper radius than the upper curve.

Neither radius is given.

He wants the upper curve to be supported by a wooden trestle, and the lower track approaches the tunnel at ground level.

Have I got that right?

Now, if memory serves, a wooden trestle bent has cross members about every 12 to 16 scale feet, maybe even stretched to 20 feet sometimes. In 0 scale, that is every 4 - 5 inches.

(http://freightsheds.largescalecentral.com/users/ccsii/photos/Trestle.jpg)

Let us remove the lower two cross members, as well as the interior vertical supports, and double or triple up the lowest remaining cross member. From there, you can drop vertical or angled supports to the foundation, leaving open sufficient room for the right of way. Make however many you need.

I hope that description suffices, because I have no talent at drawing.

OR, another approach is to treat the lower track as a “river” and use a girder bridge from the last trestle bent to the upper tunnel opening, thereby removing the need for this Rube Goldberg monstrosity/

#16

Hope this works, I’ll post the explanation in a subsequent post.

Doesn’t work.

I uploaded the track plan to the same album the bent was in, freight shed doesn’t see it. I go to my albums and there it is. I delete the bent design so that the only two photos are my profile and my trackplan, edit this post and choose freight shed, and there is the deleted trestle plan and no trackplan. I go to my albums and there is the track plan (even shows on the home page) Edit-there is the deleted picture and no track plan.

My next try will to be to add a new place holder message and try to find it from the new edit.

#17

Here we go.

Sure enough, there is the deleted trestle bent plan. What are we running on, a Tandy computer?

I really appreciate all the help every one is trying to give me. I shall return.

I’m back. I deleted all of my albums, my albums tells me I have no albums, freight shed in the edit part of this message brings up the bent plan.

#18

As Count Basie used to say:“One more once.”

I had to shut down and restart my computer. apparently my browser cache was holding all the old stuff in place.

(http://freightsheds.largescalecentral.com/users/ccsii/photos/track plan.jpg)

The dark blue is the lower level On30 (there is an Fn3 level below that but we won’t go there now.) The red is the upper level, essentially a loop that passes over french doors at the bottom of the plan. Dashed red and blue are hidden tracks. The two faint partial ellipses at the top of the plan are structural elements that cannot be pierced by the upper level. My plan is to scenic them down to the lower level and up to the sloped ceiling about two feet above the upper level track.

The left hand side of the layout is mining-desert red rock that goes up to ten feet or so. The right hand side is logging in granite cliffs that go up to twelve feet or so.

The pale turquoise is the room and the lower level bench work. The space is roughly sixteen by sixteen feet. In the top left corner there are two lift out sections that will be truss bridges. The thick black lines represent trestle bents (afraid to type that for fear the dreaded bent plan will reappear) the green figures are scenery, the dashed green lines are the approximate terrain backbones. The dashed red line at the top of the plan runs in a cove that hides it. The long straight line at the bottom of the plan runs over french doors.

What have I left out?

Charley

#19

Oh, and the point in question is in the upper left corner, coming off of the lift out and going into the left structural element.

#20

I would say the ideal way to go is, as has been said earlier, a steal deck or through truss bridge over the lower track. about half way through the curve you would build a steel support to replace the bent that “should” be there. the outriggers would be outside the clearance points of the lower track with a lattice work girder (doubled)(keeping with your era) to support the middle of the upper bridge. Same way the prototype did in many places were they had another track or some other impediment in the way. Some where in Trains there is a picture from the 50’s of 3 railroads crossing each other - one on the ground, 2 on bridges above one another. The top RR had to support their bridge over the middle RR in a similar fashion. If I can find the picture, I will post it.