Boller & Hodge Standard
I found a drawing of a bridge shoe that looked like it would work for what I needed. (meaning it was simple enough). I found this is a book titled “Types and Details of Bridge Construction: Plate girders – by Frank Woodward Skinner and published in 1906. On page 158 there is a nice drawing of a Boller & Hodge standard bridge shoe along with the following:
“Boiler & Hodge. — Messrs. Boiler & Hodge, New York, have designed standard sets of cast-iron shoes and pedestals for plate-girder supports which have been used for a large number of railroad bridges. The smallest has a base of 16 in. square and the lengths of the sides vary by increments of 4 in.
They are designed to distribute the loads uniformly on the base and to reduce the intensity of pressure to 200 lbs. per sq. in. on the concrete on which the pedestals are assumed to be supported, or the equivalent cement mortar with which they are leveled up on stone seats. They are made of tough gray cast-iron, which it is specified must be strong enough for a sample test piece 1 in. square and 12 in. long to bear a center bending load of 2500 lbs. The thickness of the metal varies from 7/8 to 1-3/4 in., and all angles are filleted with a radius of 1 in.
Short -span girders have both ends fixed and seated on single-piece pedestals with planed flat tops supported on longitudinal and transverse vertical webs. The bottom flanges of the girders are secured to the pedestals by four 7/8-in. bolts, and the pedestals are fastened to the masonry by two 1-1/4-in stone bolts 15 in. long. The largest size is 36 in. wide, 26 in. long, weighs with bolts 825 lbs., and has a capacity of 185,600 lbs.” 1
The point of copying and pasting all of that is – this is good info for the modeler. We are of course going to modify everything to fit our modeling – the changes we have based on the materials we have to attempt to replicate it. The important thing is that this is starting point we can work toward. We have dimensions, bolt sizes and so on.
Copy in 1:48
Here’s the result in O scale. The smallest supported wall that Shapeways will print in their Fine Detail PLastic is .3mm .. if an unsupported wall then it goes to .6mm … that is respectively 0.012″ and 0.024″ … or full-size ~ 9/16″ and 1-3/16″.
Looking at the drawing to the left that means this would have been 0.385″/18-1/2″ long, 0.270″/13″ wide and 0.221″/10-5/8″ high. The numbers don’t really mean anything .. I’m not an engineer .. I am more of a … Guess-gineer
If you look back at the original drawing, the actual bearing surface is 12-1/2″ x 16″. This is where I can do some Guess-gineering. A rectangle measuring 12.5″ x 16″ gives us 200 sq. in with 51,000 lbs bearing capacity. That means each sq. in. is supporting 255 lbs. My design has a bearing surface of 18.5″ x 13″ which gives 240 sq. in. Continuing with that then … 240 x 255 = 61,200 lbs bearing capacity.
That may not be great Engineering but works fine for Guess-gineering. We can find similar bridges in design and length to get a guessed weight and design our bridge shoes for that load.
On the right a version printed in WSF … White Strong and Flexible .. a Sintered Nylon. The one on the far right was colored by brushing on a AI mixture.