Bascule Bridge
08/30/2002
External Reference:
Any time you want to build a bridge for your model railroad you will want to consult Kalmbach Books' "Model Railroad Bridges & Trestles". I have read this book through a number of times. I needed a bridge that covered a 277-foot span river. Even though I would have loved to have seen it actually operate, the combination of this being my first scratch-build project, and the complexity of this type of bridge, I decided to make it a static model. However, since this river had lots of traffic (near a harbor), I needed to build a bridge that looked like one that is movable in the real world. After much pondering, I decided on something similar to the "B & OCT Bascule Bridge" (Baltimore & Ohio Chicago Terminal Railroad) on page 142 of the above-mentioned book. The article in the book is relatively sparse on technical details in the text, but it comes with a 1/2-N-scale drawing (front, rear, side, and top views). It also has an exploded view of the three types of girders used on this bridge. The article contains 4 B&W photos of the prototype model. So, hungering for more information, I turned to the Internet, and hit my favorite search engine. Quite quickly I found the "FEC Strauss Bascule Bridge" web page. The owner of this site spent a significant amount of time and effort taking photos of the entire bridge inside-out, upside-down, and in-between. Also, it appears that he is a modeler, so he included lots of technical details.

At the beginning of the movie "Excess Baggage" with Alicia Silverstone, a shot of a opening bascule bridge is clearly visible. There are two such bridges next to each other. One was closed and the other was in motion. There are other close-up shots of structural beams of bridges throughout this movie. The photo below was taken by Len Moss, who has graciously allowed me to show it here on my web site. It is his photo of the bridge shown in the movie. Thank you, Len! The bridge is the Johnson Street Bridge in Victoria, B.C. (thanks to John MacEdward for the data).
(photo: copyright Len Moss, used by permission)
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My model bridge needed to cover a scale 277-foot span. The double mainline of the layout was 20 feet apart (center-to-center) at that location. I calculated I needed to have about a 40-foot wide bridge to provide walk space and space taken up by the structural beams. The river top was 17 feet below the rail tops on one side and of the bridge and 16 feet below on the other. Most of the design for this bridge came from spending lots of time studying the photos of the FEC Strauss Bascule Bridge on the site mentioned above. By magnifying the photos you can get a pretty good impression of how the bridge was built. I had bought a Plastruct N-scale bridge kit, so I am using the raw materials from that kit for this scratch-building project. The base frame of the bridge starts off with two sets of H columns. To ensure that the H-columns are perfectly straight, I drew a line on a piece of flat 3/4" plywood and glued four pieces of strip wood along it. The photo below shows the strip wood, and the pencil line. I used regular wood glue and my favorite glue dispenser - the toothpick.
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I glued two 12-inch pieces of 2.5' x 2.5' H-beams butt-to-butt. This makes the basic length-wise span of the structure. I am using Testors Plastic Cement for the glue.
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The H-columns then rest against the strip wood pieces.
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I used the square to line up the first 35-foot I-beam that spans the distance between the two parallel H-columns. The I-beam is 1 foot wide and 2.5 feet tall.
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I then continued to place more I-beams at a distance of 40 feet on center. This means that each bridge span section is a nice 40-foot square. I will need 6 of these and then two 18-foot sections on the ends of the bridge to make the total 277 feet.
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Here is the completed ladder frame. After installing all the I-beams, I glued the other H-column span to the ends of the cross beams.
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Now that the basic frame is in place, I need to work on lateral structural support. The diagonal cross beams are going to be mounted to gusset plates, so these plates need to go in first. I decided on a scale 5ft x 5ft plate chamfered at the corners.
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The dominant cross beam is a T-shape of about 1 foot wide and 1 foot tall. This provides structural support between the spans (it keeps the bridge straight). I did this in a zig-zag pattern across the whole structure. These beams are glued to the top side of the gusset plate.
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The cross beam for the other corners are just 2-foot wide flat steel beams. They are connected to the gusset plates and attached to the under side of the T-shape beams mentioned above. I carefully cut these strips using an exacto knife and a ruler.
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Next up are the tie and track support. It consists of two I-beams that run the length of the bridge. These beams are 3.5 feet tall and 1.5 feet wide. The two beams are separated by a 6-foot stretch of the same I-beam. This makes the support structure 9 feet wide - the width of the bridge track ties.
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Glue may be sufficient to hold the model together, in the real world they use gusset plates. I made 32 gusset plates that are 3 feet square, with their corners chopped off.
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Here's a close-up of those gussetts installed.
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The foundation structure of the bridge is now complete. What you see here is the ladder framework on the bottom and the two track support structures glued on top. The track supports have been placed such that they line up with the track that is already in place on the layout. Gluing these three components together finally made the whole structure solid. It was a very exciting and satisfying moment to see all this coming together.
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This is the board walk between the two tracks (the photo is over-exposed). This is, I assume, where the bridge maintenance crew walked. Also, should the train need to make an emergency stop on the bridge, passengers would be able to exit the cars on foot. This board walk was made out of strip wood. The individual boards are 12 inches wide and 6 inches thick. The total number of boards across is 13. The board walk spans the entire bridge span (277 feet). The boards were glued to 12" x 12" strip boards underneath (you can barely see them on the large photo). These boards will not be visible when the bridge is installed, so I didn't make them prototypical - just functional.
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I then glued the board walk supports. They are 2.5 feet by 1 foot I-beams. Again, they are purely for functional support rather than necessarily being prototypical.
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The board walk with a brown stain applied. I also covered it with an India ink mixture to show the grain and board sections better. I just placed the board walk on the frame; it is not glued down yet.
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Now that the bottom frame is done it is time to focus my attention to the top part of the structure. This is a lot more complicated. In addition to the more traditional overhead truss structure, there is also the integration with the A frame structure that holds the motor house and the lifting structure. The vertical posts are made out of 2.5' x 2.5' H-beams.
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I did the same thing on the other side. Each column is 35 feet tall. This should provide for enough clearance for the trains and the overhead structure. I have decided on a simpler overhead design than what the FEC Strauss Bascule Bridge has. I will get to that later. The horizontal top beams have been installed. These are also 2.5' x 2.5' H-beams.
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The angled support beams at the end of the bridge have been cut and glued into place. This is just a temporary set-up. I just wanted to see if it all fits. The track is just loose flextrack with power only being supplied via the rail joiners.
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The diagonal I-beams have been installed.
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Again, off to cutting and gluing more gusset plates. This time to make sure the horizontal and diagonal beams don't wander off somewhere when a heavy diesel comes thundering by. The gussets are 4ft by 4ft plates cut similarly to the ones above.
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Today's task? 62 gusset plates. This photo shows where I am working on cutting 4-foot by 7-foot plates.
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Next, the overhead horizontal braces were installed. These were made out of 3.5 feet by 1.5 feet I-beams. I used a C-clamp to hold the two sides together after putting the bridge upside down. This made it possible to fine-tune the braces. After the glue dried they were in there nice and tight and the bridge is square.
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This is a close-up of the gusset for the motor house side of the bridge span. This is where the lifting mechanism will eventually be attached. It was made out of a sheet of 8-foot by 10-foot with corners trimmed to fit the shape of the bridge beams.
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I took two T-beams (1-foot by 1-foot) and cut them such that they make a lap joint much like you would do for woodworking. This was definitely work that required the magnifying glasses and a steady hand.
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Here they are dry-fitted.
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While the two T-beams were in a stable position on the bridge and their location matched their eventual position, I placed a drop of glue in their intersection to hold them together. This glue joint is not strong enough (neither in the model world nor in the real one), so I cut a piece of 3-foot by 3-foot gusset, trimmed each of the four corners, and glued it on top of the intersection. It was now strong enough to be lifted off the structure. I also marked with a pen where to cut the four ends of the T-beams. I used rail nippers to make the cuts.
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The diagonal support for the motor house end of the bridge still had to be installed. I ran out of I-beam material, so I fabricated one from a channel beam with two strips of styrene glued to the edges of the flat side of the channel.
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A smaller support structure across the span of the bridge can be clearly seen here because of the white styrene. This is the end of the bridge. The clearance is around 25 feet from the rail tops.
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And here is the motor house side of the bridge with its corresponding structure made out of white styrene.
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The basic structure of the movable section of the bascule bridge is now complete. I have spent a total of 31 hours in building this section of the bridge. Next, I am off to the paint shop for a coat of gray primer...
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I spray painted the entire structure with a primer gray, typically used for automotive priming. It works well, however you do have to watch for quick build-up. The lesson learned from spraying the bottom structure before building the super structure was, don't do it! Whenever plastics still need to be glued onto a structure, I will not pre-paint anything. Scraping off the paint from areas where the paint accidentally landed is very time-consuming. All that is left to do on this structure is glue the track and wooden walkway in between the tracks. I plan on doing that with slow-setting epoxy glue because of the dissimilar materials, hence the spray painting now. In the photo, the model has been painted with Poly S "Stainless Steel". It took 4 hours over three nights.
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Technically, the bridge isn't finished yet. The motor house and the weight structure still needed to be built. I never got around to doing that. I did, however, successfully use the bridge in the layout (see photo below). The only problem I found was that the bridge wasn't wide enough. If a locomotive engineer stuck out his hand from the engine's window, he would hit the structure! The related problem was that the spacing between the double-track mainline on that layout was too wide.
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