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This is a step by step explanation of the assembly procedure of a partially subdivided Pratt bridge for my railway and is also an example of building a custom kit bridge, if one was purchased from Diversions.  The reason this bridge qualifies as a partially subdivided Pratt is the four angled braces on the ends of the major trusses.  In order for a bridge to carry more weight, more subdivisions of the basic triangle shape can be added to increase the load carrying capacity of a Pratt bridge.  This bridge will have two twin spans supported by a center pier on my railway.

The first 2 figures here, V1 and V2 show the virtual model fully assembled and broken out into the FDM machines build components.  The creation of the STL files were done in Studio Max.

Figures 1 thru 6  show the FDM build still on it's support block and surrounded by the support material used by the machine.  Figure 1 is the lower beam and X bracing of the arch.  Figure 2 shows the upper arch beams and the large X braces for the under side of the floor stringer.  Figure 3 shows the floor stringer, the gusset plates between the floor and the arch, the upper trusses and the necessary gusset plates for them. Figure 4 shows the vertical and angle beams and their included Z bracing.  Figure 5 shows the major X beams in the center panel and the subdivision beams for the ends of the arch.  Figure 6 shows the upper most X bracing across the top of the arches and the skew blocks.

Figures 7, 8, 9, 10, 11 and 12 show the above components removed from their support material and in the case of Figures 10 and 11 the Z bracing has already been added to the beams.

Figure 13 shows the assembled lower beams of the arches.  Figure 14 shows the large X bracing added to the floor stringer.  Figure 15 shows the four vertical beams and 2 angled supports added to the lower beams.  Figure 16 shows the first angled brace of the center X bracing. Figure 17 shows the completion of the X bracing in the center panel.  Figure 18 shows the addition of the upper arch and the subdividing braces which completes the arches. 

Figures 19 and 20 show the addition of the first arch and the triangular gusset plates to the floor stringer.  Figures 21 and 22 show the addition of the second arch and gusset plates.  Figures 23 and 24 show the addition of the 4 top trusses connecting the arches.

Figure 25 shows the addition of the top X brace truss and the associated gussets.  Figures 26 and 27 show the completed bridge.

The painted bridge installed on the railway.

IMG_1173.JPG IMG_1171.JPG IMG_1170.JPG IMG_1174.JPG IMG_1175.JPG Pratt Bridge