Thomas Viaduct

from  https://en.wikipedia.org/wiki/Thomas_Viaduct

Interestingly, it was commisioned and built so early on by B&O's first president,...and its still in use TODAY !!

18 Photos

18 other photos
https://loc.gov/pictures/search/?q=Photograph:%20md0802&fi=number&op=PHRASE&va=exact&co%20=hh&st=gallery&sg%20=%20true
 

...and one of a single arch that I will try to get somewhat correct depending on my layouts geometry.

The main design problem to overcome was that of constructing such a large bridge on a curve. The design called for several variations in span and  pier widths between the opposite sides of the structure. This problem was solved by having the lateral pier faces laid out on radial lines, making the piers essentially wedge-shaped and fitted to the 4-degree curve.

Looks today vs yesteryear

http://thomas-viaduct-relay-maryland.blogspot.com/2014/06/thomas-viaduct-history-historic_5436.html
(great photos also)

2 Zones of viaduct, single track & double track

Here are the two zones of my viaduct marked out with the yellow marks. On the right side of the dwg is the double  track 2 mainlines leading up most of that side from its start down in the lower end, up to the tunnel entrance to the helix at the back wall.

The single track portion is represented by that track that that splits off of one of the double track mainlines just prior to entering the helix portal and travels along the back wall to curve down and eventually join back in with the inboard mainline down the left side of the layout. This is my 'alternative track' that allows a trains to run continuous loops around the lower level of the layout without having to climb the helix each time.

In both cases the viaduct(s) climb over two different tracks at their upper heights,...near the helix portal.
The longer double track portion climbs a 2.64% grade,... best I can do at the moment.
I'm not even going to mention the grade for the shorter single track portion at this time, as I am sure I will get many naysayers. Lets just say that I envision that in MOST cases the trains will be running down this grade, not up it.

 

Very rough mock-up at the beginning,...those blocks of wood are not the correct height

And those sheets of foamcore standing vertical are no where near correct,...just spare pieces thrown up to approx the outer reaches of the Balt city scene. And that viaduct there is an older plastic one I happen to have laying around.

(I was originally planning on letting the Balt property line come out and cover that curved track exiting/entering the back wall. but there were some problems there with incorporating the viaduct directly into that 'property line' with the city, so I thought it best to put the city line in back of that curved track. I think I will now let that curved track behind the viaduct be one that is exciting/entering the 'harbor tunnel' of Balt)

...working on my arch shapes/dimensions today

Turntable Cutout

Glad I did NOT cut the hole for my turntable yet. I relocated it just slightly once before, and now it appears I will have to make another 'adjustment'.

Could be impressive

Sure looks like an interesting project. When you get it done, please give photos. It has been done by others. But you have an opportunity to do as well or better.

tracks underneath

Ran into a problem with sizing the arches such that one of those tracks (at least the one that passes at an angle other than 90 degrees) could run underneath. I happen to have a dbl-track curved cord bridge that I placed over that track. May have to utilize that to span some distance between 2 segments of the viaduct. 

 
 

I was cruising thru the forums looking for something else, when I ran across this rather 'unique' bridge subject thread,

Unique Bridge,   https://forum.mrhmag.com/post/unique-literally-bridge-12196520

At first I left the stone arches out from under where the curved cord bridge was, ...something like the appearance of this,..

 

But I was not to thrilled with the square-ess opening. I'm going to see if I can include the arches underneath the curved cord bridge,.... like what might have occurred if the stone arch bridge was later in life modified to have a wider opening by hollowing out the interior of the original bridge while retaining the exterior sidewall arches.

Bellaire Ohio, Great Stone Viaduct

Now I know where I saw some of those single track stone viaducts that B&O utilized. They were in Bellaire, Ohio
 

https://remarkableohio.org/index.php?/category/76

Arch Shape

I was looking for the shape of the arches as they got down to ground level,....just a bit hard to determine here, but only photo I found so far
 

https://thecourier.typepad.com/.a/6a00d834ca83d669e201a73df4cf6c970d-500wi

Scratch Building with Plaster

Scratch Building with Plaster Mold

http://www.gatewaynmra.org/2010/casting-and-scratch-building-stone-arch-viaduct/

Arch Bridge from Plaster

These bridges have always impressed me, both for their beauty and as testaments to the skills of the early railroad builders. One in particular I’d like to Model is the B&O single track one heading heading into Wheeling from Pittsburgh. The line emerges from a tunnel, bridges another line at right angles then immediately enters the long curving viaduct. After the line crosses the valley the viaduct spans it curves into the city of Wheeling, using street running to pass through part of the way. It would make a great modeling project if a person had about 8-10 feet to fit it in.

One very usable plaster casting technique is presented in the old Kalmbach softcover book, “HO Railroad That Grows”. Some modeling ideas are oldies but still goodies.

Barry P

At some point as the viaduct gets closer to ground level they

would use fill for a ramp up to the viaduct.  If you look closely at the steel arch bridge in the center of an arch viaduct, you will notice that the steel arch is not squared off.  Instead the stone viaduct is squared off on either end of the steel arch and the steel arch continues all the way down part of the squared off end of the viaduct arches on both ends.  If the steel arch is cut off to blend into the stone instead of the other way around, I think the steel arch looses strength.  

Geometry !

In my younger days I was superb at geometry and math, but I think those days are over .

I've spent the last 3-4 days trying to work out the dimensions for the arches (narrowed down to 2 now), and the grades tracks in the curves, the heights of the risers in the curves, and the other spacing interference with other tracks, etc, etc.

But in doing so I have come up with construction ideas utilizing the foam-core I collected up as scrap from the sign shop,...ideas for both this viaduct, and my elevated track on the upper deck logging area.

Last night I water tested some of this foam-core product I salvaged, and it turned out GREAT. Its also easy to cut with a fine tooth jig saw blade, and a fine tooth hand saw blade. It did not do well with a fine tooth hack saw blade, nor one of those vibration cutters? I must visit my sign shop on Mon or Tues and find out exactly what material i have here, as their are no ID markings.

Construction Material Ideas

I have several construction ideas at the moment:

1) One similar to what Michael is doing here with Taskboard
https://forum.mrhmag.com/post/the-breitenbach-rosenheim-railroad-v3-12210516

2) A similar idea but using this foam-core product I found as a substructure, and layering on a cosmetic covering

....this foam core i just did a little water test with,...
https://forum.mrhmag.com/post/elmers-foamcore-enhancement-12213432

Suggestions

Foam can be embossed with a form.

An old paint brush without brushes can be formed with a plier as a rectangular fashion tool to simulatre bricks or stone.

Tapping the embossed surface with a old tooth brush give relief and irregulaities to the stones

The foam board can be used for this purpose just by peeling of the cardstock sheet, may be it could be curved, but not sure.

You can also cut the whole arched assembly in a thick foam piece blue or pink and emboss the massive pieces of the bidges in stones relief.

Big work, many times and lot of patience, not for me .

NOCH offer  embossed foam stones on big board, don't know if you are able to curve them.

You can also use a styrene skeleton and glue on stones plastic plate like the  KIBRI ones or use the  flexible stone pattern made by CHOOCH and cut the pieces to fit the skeleton.

A kitbash could be possible with some old FALLER stone arched bridge or the ATLAS one, research on the web for references, if out of production look at E bay.

You can do a master, make a rubber mold of the master and build the bridge in plaster.

The old FALLER stone bridge is a good start for a good master or the stones plates made by KIBRI

Or also make the whole bridge in thin plywood and glue plaster stone molds and carve them to fit on the plywood structure.

You can also use modeling paste, glued on the plywood form and carved like the foam.....good luck !

Or a custom order for a laser engraving work on a big plate and you cut it in form to reduce cost.

Just some suggestions.

And some link about stone wall scratch and kit build

Marc

multiple links

Thanks for those multiple links Marc. I'll have a look later today, this evening. Right now I've got to get back to more sawing/gluing of my mock-up.

Foam-core Mock-up

This foam-core mock-up was originally going to be just that,...a mock-up. But I have discovered that this particular foam-core product is much more deserving of being the actual structural portion of the finished product,....then cosmetic skins added to this backbone structure.

 

I started out using some 1/4” thick material for the roadbed. Then I experimented around with the arch dimensions. I ended up with 2 arch dimensions,...a 6” inch center-to-center column dimension with a 5” dia arch,...and a 5” cen-to-cen one with a 4” dia arch

 
….the larger arch for the double track portion and the smaller arch for the single track portion.

In order to make those arches line up I spaced them along the inboard edge of the rising bridge roadbed,...every 6'' for the double track portion. So now I knew where my risers needed to be,...behind the vertical columns of those arches. I cut these risers out of 1/2” foam-core,..the same type of material I had on hand for the roadbed. But every 6” ?....not really necessary for supporting that foam-core roadbed. AND then I doubled up the thickness of the risers by gluing two side-by-side making them 1” thick risers...overkill, but I will explain my reasoning later.

Now I had to get the height of each of those multiple risers correct. I measured my ultimate rise, my minimum rise. And the curving lineal distance along the roadbed between those 2 points. I plotted those two heights on the edge of my plywood work table and drew a straight line between them. Now I could go to any point along that line and measure what height riser I needed.

 
(BTW, my plywood work table was NOT long enough to get the whole distance in there, so I had to add a temp alum beam to the edge of that table to get an extra 40 + inches in there).

I am going to make the risers the same width as my roadbed, 5”, so I cut a 5” wide strip of 1/2” foam-core, then proceeded to cut off the different height risers. Turns out I need to cut 2 pieces for each riser location so I could double them up to get my 1” thick riser.

Thats where I am today.

I like the simplicity of this approach

I like the simplicity of this approach Marc

Just need to find a good existing pattern.

Or I wonder in this modern day if such a 'skin covering' could be created by some photographic/printing process like they use to create backgound scenes?

Not much progress today

Didn't get too much done today,..lots of interruptions

But I did take the arches out from under the bridge (they are just manila folder paper cut-outs), and I am growing more fond of that idea.

In a curved viaduct, the

In a curved viaduct, the external length of a span is bigger than the inner. If the arch of the span is not skewed, then the piers have to have thicker the outer face dimension, a trapezoidal cross section. 
I don't understand the use of a larger span in the double track bridge than the single track, but if everything will be in proportion then ok.

close to the walls & size of arches

For the most part my arch bridges are going to be fairly close to their back walls,...and/or their backsides are not going to be viewable. So it was my intention to leave off the decorative facings on the back sides.

The two different size arches came about as a result of the spacing of those 2 tracks passing underneath, and the bridge in that one section. Turns out that bridge is 18" long, so divided by 3 it came out to 6" each arch span. I then made the manila paper cut out and it looked good.

When I extended that on towards where the single track curved off to the left and crossed that other track the continued 6" spacing did not work out correctly. So I made the smaller arch at 5". Wala, it worked out just fine. So I just chose to make the single track section all in 5" arches.

I had wanted to limit the number of different size arches, thinking I might end up making duplicate moldings, or duplicate somethings. At the moment I think I have that with only 2 different sizes,...and their legs can be shortened as the grade drops in elevation.

Wonder if I can get someone to create a nice 'master plug' of those 2 arches, that I could take and mold duplicates of?   The vertical joint lines would be covered by a third molding of that proud portion on the columns in the original bridge.
Check out the 2 photos HERE
https://forum.mrhmag.com/post/stone-arch-viaduct-bridge-12213517

How Thin

BTW, how thin can you mold things these days, and what materials?  (1/16")??

The arch 'plates' would not be structural at all, just decorative.

Making Arches

I just made this posting asking about make 'plugs' to create molds for the arches with a laser
https://forum.mrhmag.com/post/if-you-can-have-only-one-which-and-why-12209250
 

Then I ran across these postings,..

Moving my other posting

About an hour ago I made this posting to a subject thread that had a lot of interesting participants, BUT it was titled very badly to attract the subject under discussion. So I am moving my question from that thread back over where it will get more attention/responses