Model Railway Viaduct

(A Work In Progress)

What is a viaduct?

A viaduct is a bridge consisting of a series of spans or arches that is used to carry a railway / railroad, or road  over a wide valley. In terms of a railway viaduct these are usually built to join two areas of equal height to allow the railway to remain level and thus to allow for the fast running of trains.

Where as it is easy for a train to turn left or right it is not easy for a train to go up or down. Trains can only cope with a gradual gradient change. This is why railways often meander through the countryside following the contours of the land as well as avoiding natural obstacles like rivers. The Great Western Railway probably the most famous railway in the world, built buy Isambard Kingdom Brunel was given the nickname the "Great Way Round" due to the fact that it's routes were not the most direct because they followed the contours of the land giving the railway the most level and smooth ride possible. It is a testament to how level and smooth the railway line was that today it can carry HST's at 125mph without modification to the line.

When it is not possible to follow the contours such as across areas with hills and valleys, the railway builders used a technique called cut and fill were you cut out a some of the hill to lower the level of the track bed and then use the fill to build up the level of the track bed in the valley. Where this was not an option they then had to turn to constructed embankments, bridges and in the deepest and longest valleys, Viaducts. Likewise with hills they first dug cuttings then cuttings with supported sides and then for the biggest hills they built tunnels to go through them.

My reason for building a railway viaduct.

The modular layout I choose to build required a removable section of tract to allow entry and exit from the inner circle of the layout when not in use. My decision was to construct a thin board to carry two running tracks across the gap in my layout. Once constructed it immediately came to mind that it was the perfect shape to be turned into a bridge.

The reason I choose a viaduct bridge was because it fit the shape and size of the bridge and by using a viaduct rather than a more modern design of bridge I would not date the layout thus allowing me to run steam and modern diesel and electric trains without them looking out of place.

I also had access to a brick pattern and by using this it would tie the bridge into the tunnel portals which will also be covered with the same brick pattern.

Railway Viaduct Resources

For more pictures visit Railway Pictures at www.railwaypictures.co.uk and search for viaduct

Brick Pattern used: word document (brick pattern was resized)

How to build a Model Railway Viaduct?

Materials:

16 x printed sheets of brick pattern.

2 x A1 size 1mm mounting card.

PVA glue

Note: (It is assumed that you have already built a board to carry the track bed. Below gives instructions for decorating this board to look like a viaduct).

You can also build the viaduct out of ply, mdf etc, but I choose card to keep the weight down.

Tools:

scissors, craft knife, cutting mat, metal rule, a round plate or other round item, pencil and pegs.

Instructions:

The first stage was to measure and cut out the sides of the viaduct. For this I used the 1mm mounting card which I measured and drew on the shape I wanted for the viaduct. There are so many different designs that you have a lot of freedom in your choice. I worked out I could have 4  arches on my bridge The arches were never intended to go down much further than the point at which the aches stop and the abutments start as I will need to crawl underneath it when I am running the layout to get in and out. Thus the viaduct is more of a representation of the top of one.

My arches are 22cm across and have abutments that are 4 cm wide. I have also allowed 2cm above the track bed to act as a wall for the top of the viaduct.

Once you have cut out both of your viaduct sides you will need to fix them (I used PVA) to your track bed making sure the arches are opposite to each other and that they are spaced an equal distance from each other (square). In my case I also had to make sure the wall at the top of the viaduct is the same height across the length of the bridge. Once the glue has dried you can start strengthening the structure.

To make the viaducts arches strong and ridged I decided to glue pieces of card between the two railway viaducts legs. I laid the bridge on it's side, inserted the glued sections of card making sure the viaducts sides remained square and straight. I then placed weights on top of each leg until the PVA glue dried. Once dried this created a very strong and ridged structure.

To build the sides and roof of the arches I first needed to measure the distance between each viaduct side. I then added 1cm each side which will be used as a gluing surface to hold the arch in place. I came to the conclusion that I would only build part of the arches as I needed some where to hold on to when I need to remove the viaduct section of board from the layout.

After you have cut out the section of arch wall I scored down both sides 1cm in from the edge and then bent the card over to make a right angle. I then put slits into the extra bit of card that was bent over, to allow the card to follow the curve in the bridge. These extra tabs that I had created are to allow me to glue the viaducts walls in place (see picture below).

I then glued the side wall in place following the curve in the viaducts arch wall (see pictures below). To hold this in place I used some small clamps (I also used pegs).

This process was repeated seven times more until all the arches had side walls. As you can see from the pictures shown below you will need a lot of clamps or pegs.

The next step was to cover the viaduct with a decorative covering of brick or stone (various colours). I choose to use the brick pattern, which is available in the download section, to cover the viaduct in a red / blue brick colour and pattern. It was a simple process of cutting away any of the white paper left after printing and then gluing the sheets onto the viaducts sides with a thin layer of PVA glue (see picture below).

Each sheet was large enough to fit across the arch and after a few minutes of drying I cut out the centre of the arch leaving a 1cm overlap. I then cut slits in the 1cm overlap and like I did with the arch sides, I folded these over and glued them to the inside of the arch. This left a nice curved shape to the arch and will allow for some overlap in the brick pattern between the viaducts sides and the inside of the arch (see pictures below).

Once you have covered both sides in the brick pattern you can move onto the inside of the arches. Firstly you will need to cut the brick pattern paper to the correct width. When cutting you can leave some overlap at the top and bottom as you can use the excess to wrap around the end of the card which will help secure the brick pattern further. When you are happy with the size of the brick pattern paper you can glue it down with PVA.

The last step is to glue some more brick pattern paper to the inside walls of the viaduct either side of the tracks.

And your done.

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