Harthope Viaduct

Any aspect related to the structures and equipment on the Caledonian Railway Company.
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WCML55.68
Posts: 276
Joined: Sat May 31, 2014 4:37 pm

Harthope Viaduct

Post by WCML55.68 »

Morning all,

I'm thinking a wee bit ahead to the construction of the viaduct itself, still have a replacement block of 2 cottages to construct plus middens and platelayers hut and finish off the block of 4 and the dwelling house. That will be this winter.

Never built anything like this before and certainly nothing so large … in 4mm, the viaduct will be around 10" high at the deepest point and the total span length will be some 4'6" comprising 2 buttresses and 5 piers supporting 6 spans of around 9”. All but the southernmost buttress are skew. There are 5 different sizes of span (the southernmost is different both sides) although three are within 11” of each other and five different lengths of lattice parapet.
Presumably the piers would be thus spaced after surveying the site?? The longest one is over the roadway, only by nine inches, but I would imagine this would have been minor in 1875 compared to say the 1950s. I canny think of any other reason why they wouldny use a common size for the majority of the spans unless the ability to measure such distances wasny too accurate??.
Also the remnants of the 1848 viaduct comprising 2 buttresses and 2 piers will be represented, but easy-peasy compared.
Purely for interest does anyone know if any plans, pictures or etchings exist of the complete 1848 structure? Ive never discovered anything at all, only the castiron spans were demolished and the piers and buttresses remained alongside its replacement until the A74 was widened in 1964/65 when both piers were removed and the only stonework remaining has been mostly buried in the 2006 bridge renewal but what is still visible has been carefully photographed and measured.

It is very difficult to tell from looking at the LMS plans whether the deck and lattices are level or rising to match the ruling gradient of around 1 in 75 as the piers taper slightly but the southernmost buttress appears to be vertical and is deep enough to lay a 10½" engineers square against. This suggests a rise of 3½mm over the 260mm/10½" which works out at 1 in 75 and coincides with the ruling gradient so it appears the deck actually rises too.
This would be in line with actual practise??

Another thought is whether to actually lay the mainline at this steep grade, I suppose it all depends on the adhesion, ability and performance of of the motive power. "Banking" may only be reliably achievable by unpowered Fairburn/BR Standard tanks coupled at the rear as an extra vehicle. I suspect, certainly with relatively light 4w goods traffic, that mid-train derailments would occur if over pushed from the banker. Unpowered would certainly leave plenty of room for a speaker but then an identical powered version would be required for each number to represent the locos as they return to Beattock in readiness for the next banking turn.
Some experimentation is needed, does anyone have any experience or thoughts?

Lastly construction, this was my original MO.
To build on a substantial level frame with quality plywood forming a solid base just for the line of the viaduct, placed a little lower than the deepest point.
Full height piers of oblong hardwood would be accurately positioned and screwed/glued to act as supports for the deck. It would be impossible to shape these accurately to a taper. Dimensions would allow for stone facing, tops would be on the 1 in 75 rising gradient.
An alternative would be to use 80th plasticard to make the carrying piers, these could be tapered accurately and simply apply the laminate facing to these. 1” deep blocks of wood glued to baseboard to locate the piers which could then be secured with countersunk screws.
It would make sense to use marine ply for the decking to match the ply base from an expansion point of view.
The facing of the piers and the girders/lattices would be completely cosmetic.
Then build up around the Evan Water, A74 and the land around as appropriate, plans don't show height so all taken from photos. Eg the relationship between rail level and the apexes of the cottages being a very moot point as most photos are looking down or up, not level.

Im thinking of using laminated sheets of 80th plasticard with 20th stone cladding applied thereon to achieve the piers' taper shape if wooden blocks win the day.
Ive managed to find some Canadian A4 embossed plastic sheets intended for dolls houses! Regular uninterrupted 5mm courses and the length of the stones in each course do vary and its very discreetly embossed, extremely realistic and almost perfect for my needs. Although I really wanted 6mm course, this is the closest match I will ever find. The only other option, Slaters 7mm is rather over accentuated relief-wise and the courses and embossing are all over the place with some blocks covering two courses. Ive even tried back-filling this and filling/dividing the double course blocks and gently sanding to reduce the relief on the most offending stones but Im not happy with the result. It may be OK for Midland Railway, Ribblehead is similar. The Canadian stuff looks really brilliant from the start and really captures the Harthope character and will save a lot of work so the 1mm reduction in courses is small price and probably would never have been noticed.
Some 17 sheets required just for the piers but wise to obtain a good few extra whilst available.
I've been wondering whether to fill the void between cladding and hardwood with a little expanding foam to aid prevention of warping or to brace them somehow. Or to dispense with the wooden blocks altogether, assemble the piers from the facing and and rely on internal bracing or even to use expanding foam.
Any thoughts??
On top of these my feeling is either a strip of 1/8” aluminium sheet, acetate/perspex or possibly RC modellers marine ply?? Ply might be a better option as far as glueing ballast and expansion in common with the baseboard is concerned. All should more than adequately support the heaviest of locos over the 9” spans and produce a nice rumble but none will bond to Plastruct or Evergreen and the difference in expansion between the different mediums chosen does concern me. Detailed planning yet to take place but it may be possible to keep the trackbed totally separate from the rest of superstructure and screw to the piers through slightly elongated holes allowing a modicum of independent expansion.
I had toyed with either strip brass or plastic for the superstructure of the bridge. Evergreen strip and section, USA, and Plastruct section, again USA, won the day because of the huge range of both readily available and covering all needs, much less so in brass, and my being far more accomplished in the former.
It has been suggested that nickel silver may be an alternative too but for the time being, plastic.
Enough plastic strip and section is already in stock and I will try assembling one section of lattice soon to gain experience and give thought time, design and make a small jig to ease construction and ensure regularity, and see how it stands up to warping. Like the Dwelling House windows, I expect the result will be amazingly strong. But effectively all the individual sections of parapets will become one when the flangeplates are added, one 4'6” piece assembled from six shorter pieces. Strength, warping and expansion does concern me.
Much thought has been given to obtaining and using some kind of printer/cutter but I think the mountain will cause too many non-tech grey cell problems and introduce too many unnecessary complications. One option would be to have them made for me. Still thinking. But pride and preference is to make myself from scratch.

As far as the lattices are concerned, there are so many different sizes it will probably be just as easy to make them by hand rather than to draw up artwork and have them made. The sample piece will be a deciding factor.
Rivets, I'm tempted only to include the most noticeable rivets which is a double row on the top of the top flangeplate of the lattices and very visible. The single ones dotted around on the lattices and the rows around the perimeter of these and the plate girders below will be far less noticeable if missing. It would also take an eternity to represent all of these and the main intention is to capture the character of the scene as a whole rather than create something down to every last nut and bolt.
Centre-punching or a tiny drill hole might be an option or application of individually applied tiny round trackpin heads too but there is a company in USA, again, called Archers, who produce sheets of waterslide resin rivets. Expensive when first discovered and have rocketed in the last couple of years. But a distinct possibility.

https://www.ebay.co.uk/itm/170736090279 ... xy3zNSerF1

So there we have it so far.

Any thoughts or advice would be most weclome!!

Paul.

Slaters left, Canadian right
Plasticard Harthope stone cladding 1 sm.JPG
Plasticard Harthope stone cladding 1 sm.JPG (110.85 KiB) Viewed 200 times
Modified Slaters left
Plasticard Harthope stone cladding 2 sm.JPG
Plasticard Harthope stone cladding 2 sm.JPG (107.89 KiB) Viewed 200 times
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