Scratchbuilding a Deck Plate Girder Bridge

Written by Shawn Branstetter, photos by the author.

Bill of Materials

Evergreen Scale Models StyreneAk Interactive
.040 SheetAK708 Dark Rust
.010 x .250 StripAK710 Shadow Rust
.080 Angle StripAK711 Chipping Color
.015 x .080 StripAK 735 Flat Black
AK043 Medium Rust Pigment
Heavy Chipping Acrylic Fluid

There are a few of reasons why we, as model builders, scratchbuild something; either the model is not available, we are trying to match a specific prototype, or we just enjoy the challenge. For me, this project was a little bit of all the above. I was starting a really nice brass plate girder kit and was just about complete when, it jumped off the workbench and onto the concrete floor. I tried to salvage it to no avail.

So now I had to make a decision, do I purchase another kit or do I finally try my hand at building one for myself.

The pros: one, I could build it in styrene and use scale thicknesses to achieve a very realistic model. Two, I could build a bridge that fit the span I needed without having to try and modify a kit. Three, this will give me an opportunity to advance my scratchbuilding skills (which I desperately need). The cons: I have never tackled a project like this before and I’m not sure if I can do it.

Gathering Information and Data

The first step to any project like this is to gather as much prototype data as possible. Even if you are freelancing like me, staying true to prototypical standards will greatly add to the realism and believability of your models. I did a lot of reading: Model Railroad Bridges & Trestles, Kalmbach, Google searches and finally, Edward Traxler’s blog on building a plate girder bridge.

Once I had a good sense of what I was going to build, a rough sketch was made and material ordered.

Building the Structure

As previously mentioned, I am trying to make the bridge look as realistic as possible so I want the styrene material to be as close to scale as possible. Although the strips are really thin, when everything is secured in place, this bridge is suprisingly strong.

The Girder Plates are cut down from .040 styrene sheet. These plates are the structural foundation of the model, as the prototype. I used heavier styrene here just to add a little more rigidity to the overall bridge. If you are concerned about strength, the plates could be made from brass or aluminum.

The height of your girder will be determined by the typical train weight traveling over it as well as the length of the bridge. The heavier the equipment or longer the girders, the thicker, or taller your girder will be. Since my railroad is a shortline in the mid 1970’s, the equipment was moderate, trains short and the locomotives were two-axel, first or second generation GP’s (maybe some light steam if I ever back date the layout).

The first structural pieces I placed were the Flange Angles, which, are .080 styrene angle shapes. I glue them flush to the top and bottom of the outside with Testers plastic cement and allow to dry. Next I glue the inside angles in place.

Once these angles are completely dry, I can move on to the End and Intermediate Stiffeners. You will notice at this point your plates are starting to show less flex with the angels in place.

The stiffeners job is to do exactly what their name implies; stiffens the girder structure. There are a few different types of stiffeners, however, the most common I have found for my era in modeling are in the drawings above. Using the same angle material, mark your lines on the plates and glue them in place. My center stiffener was created by cutting a piece of angle material in half and glutting it to the opposite side of the angle.

Once all are in place, allow them to dry and then we can begin work on the interior bracing.

You will notice that there is no rivet detail at this point. My plan is to use decal rivets from Micro Mark. Archer also makes printed rivets that are slide decals. More about that later.

Bracing

The interior bracing may look complex, however, once you have a good idea of all your materials involved, the build moves fairly quickly.

The each one of the deck girder’s cross frame bracing consists of two horizontal bars attached to steal plates which in turn, are attached to the beams at each stiffener. Finally, two additional bars are attached like an “X” to the top and bottom with a spacing plate at the center where they cross over. It looks complicated, but it’s not.

To build these, I gathered my dimensions, cut my material to length and created a simple jig to assemble everything. The jig is nothing more than a piece of 1” x 4” scrap lumber as the base with strip wood from my scrap box used for the frame.

I glue each one together and allow them to dry before I attach them to the girder beams. You will notice that I did not glue the second cross member to the bracing yet. This was strictly a personal choice to add them once they were led to the beams.

Flange Plates

The flange plates are steal plates that run the length of the top and bottom of the beam to add even greater strength. Additional plates will be added to the top and bottom near the center outward to provide even more.

I created mine from .010 x .250 strip styrene. The strips were cemented to the top and bottom, allow to dry and then finally cut to length. Two additional plates were added to the bottom however, because you will not see the detail on top, I did not add the additional pieces to the top. After these are dry, I can move on to the bottom diagonal braces.

Diagonal Braces

To finish out the structural components, I will add the diagonal braces to the bottom of the bridge. The diagonal braces are there to prevent any sway that might occur. Heavier bridges will use a similar pattern as the interior braces, however, my bridge is light and shorter so, again, I will be using less material. Using the angle strips, cut each one to length. These are attached to the bottom of the flange angles with steal plates. Using .010 x .250 strip styrene I cut these plates to the desired length and glue them in place. Then I attach my angle braces.

As mentioned earlier, I am using printed decal rivets from Micro Mark. Archer also sells a wide variety of rivet arrangements as well. These are raised resin dots printed on slide decal paper. Since this was my first experience with them, applying them was a bit tricky at first. Soon, I got the hang of them and the process went fairly quickly although tedious.

To apply, I sprayed the entire model with gloss varnish to create a smooth surface for the decal to stick to. Working with the stiffeners first, I cut strips of rivets to length, soaked them in water and applied.

I added rivets to the bridge as the prototype, however, I did not add them to the interior. Since the detail would never be seen, I decided to leave them off.

Painting and Weathering

The entire bridge was sprayed with a foundation of Dark Rust from AK Interactive. Then I switch colors (I don’t clean my airbrush between colors) and sprayed the corners with AK Shadow Rust to add shadows in the appropriate areas.

Then, not cleaning my airbrush, I spray the interior flat black to really darken and hide the areas that are not going to be seen very well. Back to my Dark Rust color to add highlights to the bracing that will be seen followed by the shadow Shadow Rust.

Next, to add dimension to the rust and peeling paint, I brush on the Heavy Chipping Effect fluid by AK Interactive. Allow it to dry and lightly spray Chipping Color to the areas where your paint is going to be pealing. Wet a soft paint brush with water and then lightly remove color in the corners or any area you want your rust color to show through.

Now for the top coat. My bridge was, at one time, painted black. The weather and time have caused it to be mostly rust. I will brush on a large amount of the Heavy Chipping Effects and then carefully spray areas of the model. You will notice I faded the black into the rust color so you will see chipping and fading on the bridge. Again, using a soft brush with water and then lightly remove color.

To finish off the weathering, I dust on Medium Rust pigment from AK Interactive followed by real dirt. I then spray on a coat of dull varnish and then call it complete.

The completed girder bridge in place on the authors diorama.

I encourage you to try your hand at scratchbuilding. Maybe not something this size to begin, however, once you get the hang of working in your preferred building material, you will find your model building possibilities greatly increase. As will your enjoyment with the hobby. It continues to for me.

About the Author

Shawn Branstetter's picture

Shawn Branstetter

I am a graphic designer and front-end developer, creator of Shortline Modelers. I have been a life-long model railroader with a focus on California shortline and logging railroads.

Comments

ralphie79wi's picture

Shawn, great article. Nicely broken down into steps revealing that it probably isn't as hard as one might think. Great results on the color too.

Shawn Branstetter's picture

I really appreciate that. I was really surprised at just how easy it was. A little overwhelming at first.

Thanks again and welcome from a fellow proto48 newbie.

Shawn Branstetter
shortlinemodelers.com

eTraxx's picture

yeah .. great article .. and techniques .. and procedures .. and ... and .. well . all of it!

"I drank .. WHAT?"
--- Socrates

Shawn Branstetter's picture

I really appreciate that Ed! Thank you.

Shawn Branstetter
shortlinemodelers.com