I took Plastruct's bridge kit and drastically modified it making it from a through truss bridge to a deck truss bridge. This change required me to re-draw the entire bridge in Coreldraw, print it out in 1:1 scale (1:48) and build the bridge directly over the plans using T-pins like building a model airplane. My work bench's top surface is Homasote which is a great surface to hold T-pins. I tape the plans to the Homasote and then cover with some polyethylene film so nothing sticks to the plans. I used the H-, I- and T-Beams that came with the plastruct kit, and also used the sheet ABS for the gusset plates. Instead of embossing rivets into the plates, I used Archer Decals rivets which worked nicely. I used Plastruct's instructions on handling the joinery details, but applied them to my plans.
To cut the gussets, I printed out the gusset patterns on plain paper, temporarily adhered it to the ABS and used a scissors to cut them out. Gluing gussets to the bridge was all done with Bondene liquid plastic cement.
The top and bottom longitudinal members have to be continuous pieces if possible. The top rail is Ross Bridge Rail with the guard rails included. The design of the deck truss has another set of longerons directly under the running rails.
Archer Decals applied. The gussets actually comprised all the primary strength of the build. The individual joints of the members to each other was secondary.
The twin bridges are very strong and could probably each support 50 pounds or more. A 12 pound loco going across causes no deflection at all.
Here's a drawing I made. Also attached is a full-size PDF of the same. You can print it out on multiple pieces of paper and tape them together to make the building pattern.
