29. Through and Deck Plate Girder Bridges

(From How to Build Model Railroads and Equipment by Barton K Davis Copyright 1956)

You might not hear a thunderous rumble as your hotshot freight crosses either of the bridges pictured here, but the thrill of seeing any train thread across one of them and go on into the open countryside will be ample justification for having such a model on your layout. Bridges like these can be found literally by the thousands on the railroads of America. For short spans they fill the bill on just about every type of overhead crossing, from a river to a modern highway underpass.

The structures shown in Figs. I and 2 possess nearly identical dimensions and can be built from scratch, using some of the spare materials from your workshop or scrap box. And they're fun to have on the pike, for they break up the sameness of long stretches of trackage and add variety to the local scene.



Fig. I shows that this bridge is built up of a floor structure, the side or through girders, and the foundation. Build the girders first. Select a flat piece of l/~s" pine or plywood and cut two pieces, each measuring 9' 3" by 98' 6". Round off the top right and left corners as in Fig. I, using a 1' 9" radius. These pieces will form the web of the girders to which the flanges, stiffeners and cover plates will be attached. File all edges true and smooth; check with a square, for the flanges must lie at perfect right angles to the web of each girder to look right when the job is done.


The cover plates are made of postcard stock; all are 1' 6" wide, but they vary in length from the shortest (the top cover plate) to the longest, which spans the length of the girder around both corners and to the bases at the bottom ends as in Fig. I. Make two of each type, as you will need them for both girders. Four cover plates for the top and four for the bottom edges of the girder web complete the girders, except for the stiffeners. Cement the cover plates in place and allow cement to harden.


Cut the stiffeners from postcard stock, bending each to form an L-angle. Dimensions are given in Fig. I and in Section B-B. Rivet detail can be impressed with any sharp instrument, which has a sufficiently large tip-diameter to prevent puncturing the material. The top and base flange strips which lay flat against the web are made in the same way, and are cemented in place before the stiffeners are added. The protruding stiffener flanges at the bridge center are cemented back to back before attaching to the girder web. If you want a fully detailed bridge, then you must treat both sides of each girder in the same manner, and that will require twice the number of flange strips and stiffeners needed for use on the outsides alone.


Sections B-B and A-A show this structure to be made up simply of two longitudinal stringers and a series of transverse floor beams. Two floor beams are at the center of the bridge, and from there outward toward the ends, there is one floor beam at every other stiffener, starting with the first to the right and left of bridge center. Both the stringers and beams are notched to interlock where they join or cross, the beams having their lower halves·notched and the stringers their upper halves.

The stringers and beams are both made of soft pine. The two stringers are each 100' 6" long by 1' 6" deep by 9" wide. The ten floor beams are 16' 0" long by 1' 6" deep by 9" wide. When cutting notches, place the pieces in a vise and cut them all at the same time to be sure they will be aligned upon assembly. Locate the notches so that the beams will seat into the L-angle of the inside stiffeners. Cement the floor beams to the stringers, check for alignment and allow cement to harden. Make the joints strong, for they will bear most of the load of your heaviest equipment--locomotives.

Cut the long rail ties (part "m," Section A-A)16' by 6" by 6", to be laid atop the floor structure at each floor beam. The intermediate ties are standard or 10' in length. Using postcard or file card stock, cut the triangular stiffeners (part "g"), two for each floor beam, and set aside until final assembly. Cement or glue the ties in place, checking to see that the tie ends do not interfere with a perfect fit of the floor structure to the inside surfaces of the girders. File ends to provide clearance where necessary.

The planked walkway ("h") may be used on both sides, one side only, or omitted entirely, but the center walkway ("k") must be included. This can be easily made from pine or balsa sheet which has been scribed to simulate planking. The width of the strip will be determined by how close to the running rails you place the guard rails. After figuring this dimension, make the walkway strip. If you plan to use prefab roadbed (ties and rails attached), then check to see if your 6" by 8" guard timbers (part "j") are properly spaced to permit a good fit. Both guard timbers run the entire length of the bridge.


You can now cement or glue the floor structure to the girders, checking alignment and rigidity. Add timber guards and triangular stiffeners after the glue has set. Lastly, lay the rail and walkways. Allow the rail ends to extend beyond the ends of the bridge, and cut the running rails on your right-of-way to fit the ends of the bridge rails. The guard rails should taper to a point at the center line of the track, 10' to 20' beyond each end of the bridge .


The abutments are made up from pine and glued together. Modify the terrain work to seat the abutments properly. (Fig. I) and the half-section view of the abutment give the required dimensions. The abutment base corners are triangular in shape. The bridge support shoes are fashioned from pine and glued to the underside of the through girders. Try attaching the rail ends at the running rail level for the roadbed on both sides of the bridge, to determine the position of the bridge which, when the structure is installed, will insure level and properly aligned track. Fit the abutments to the underside of the bridge and glue in place. Shore up the abutments with plaster or wood wedges to get the alignment you want. Remove bridge for painting when you are satisfied that the mounting provisions are correct and will remain so. The entire bridge is painted a dull black and lettered in silver, white or gold, depending on the practice of your road. Install the completed model on the layout.




This type of bridge is built by the same method as the through girder model, except that in this case the ties and rails are laid on top of the structure. On a bridge of this kind a planked walkway with handrail is standard safety equipment for the protection of maintenance workers. The crossties are heavier than those used on the other bridge, as indicated by the Half Section at Center drawing. The use of X-braces gives the deck-plate bridge needed strength and rigidity, so don't omit these braces. They are spaced at every other stiffener from the bridge center out to each end.


The handrail is made from 1/32" brass wire, soldered to 1/32" wire supports spaced 7' apart for the entire length of the bridge. The wire supports are 3' high, with ends driven into pre-drilled holes at the ends of the extra-length ties, which correspond to the handrail support points in number and position. The remainder of the ties is 9' by 9" by 9". The abutments are about the same as the ones in Fig. I, except for the high back walls at the ends of the bridge. Paint the structure black; letter with a small sable brush or apply your road's decals.

Either one of these bridges will add authenticity to your pike, and also give it a new and vital look. And a custom-built bridge will increase your prestige as a model craftsman.

(From ‘How to Build Model Railroads and Equipment’ by Barton K Davis Copyright 1956) Return To "How to …Index"

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