Deck Plate Girder Bridge - Abutments
02/02/2009
For my S-scale Pennsy Branch Line layout I needed two steel plate girder deck bridges. Most of these types of bridges were built on top of cut-stone abutments. There was usually about 10ft (3m) of clearance under the bridges. All the bridges are of the open floor type (as opposed to a ballasted floor). The abutments and piers are wide enough to hold two tracks.

The abutments are meant to appear to be made out of cut stone. From studying the photos I have found, my estimate is that each of these stones measures about 16 inches high by 36 inches wide. I'm not sure how deep/thick they are. However, weeds and grasses will probably cover up the tops, so their depth is not too critical to me. The design diagram below shows the arrangements of the stone for a single-track plate girder bridge abutment (measurements are in inches). Again, by looking at prototype photos, the top row of the stack of stones is about three times the width of the ties, so about 20ft (6m). For the models I am building I need about 13ft (4m) from bottom of the ties to the top of the modeled creek, so eleven rows of stone are needed. By offsetting them with each row, the bottom row winds up being 49ft (15m) wide. The top three rows of stone are set back so as to allow for the bridge's pedestals.
Deck Plate Girder Bridge
Because I will be making two bridges, needing a total of four abutments, I decided to cast them. I have written an article about how I made the mold for these abutments. To install them on the layout, I first had to make sure the layout's surface where the abutments were to sit was actually clean and smooth. Next, I started by filing down the bottom of the abutment. Using a square, I made sure that the filing kept the bottom perpendicular to the layout's surface.
Deck Plate Girder Bridge
I kept filing down the casts until they were even with the top of the sub-roadbed, as shown in the next photo. This takes a bit of time and quite a bit of elbow grease.
Deck Plate Girder Bridge
I filed them down with two flat files. One is very rough and removes a lot of material. The other one is more gentle and allows for delicate adjustments. It generates a lot of plaster dust. The brass brush shown in the photo was used to clean the files every so often.
Deck Plate Girder Bridge
The next step was to paint and weather the abutments. The first thing I did was to cover the entire casting with India ink diluted in rubbing alcohol. The purpose of this layer is to bring out the dark shadows of the mortar lines. For the remainder I used acrylic paint thinned way down by taking a very small amount of paint and stirring it into a small container filled with water. I used these paints: Raw Sienna, Burnt Umber, Burnt Orange, Hooker's Green Deep Hue, followed by covering the entire casting with a thin layer of Yellow Oxide. Now done with all the bright colors, it was time to focus on the years of traffic on the bridge above. I used very diluted black acrylic paint to make the heavier vertical marks. I then applied several layers of diluted Charcoal Gray over the entire casting. I added even more layers (probably around 7 or 8 total) on the bottom two rows of stone. The idea is that previous high-water lines have deposited extra debris on the stone's surface. The final layer is a dry-brush application of pure white acrylic paint (undiluted). This brings out the edges of the stone and makes them look like rock. It also is used to identify streaks of bird dropping. This photo is a close-up of the finished abutment's top rows.
Deck Plate Girder Bridge
Another close-up view (kind of over-exposed).
Deck Plate Girder Bridge
The final abutment installed. I used five-minute epoxy to attach the abutment to the layout's surface after thoroughly cleaning the area.
Deck Plate Girder Bridge