|The Central Valley Model Works Plate Girder Bridge|
This was origianlly a thread on Railroad Line Forums titled – L&CRR Plate Girder Bridge
Just down from where the pump house was a need for a bridge. The On30 track that serves the Hill Valley Coke Company Coking Ovens siding is owned by the Deep river Railroad. Since the purpose of a model railroad is to have trains that run on it .. a pump house or coke ovens are of little use without a rail connection. To that end I figured I needed to get my trains running .. and for that I need to be able to cross my river.
At one time I had intended to model HOn30 .. but .. at some point I was seduced by the Dark Side. During that pre-HOn30 time I had got my clamy hands on a Central Valley Model Works #1903 72’ Plate Girder Bridge (single track).
I was happy with the kit and when I went over to On30 I decided I wanted to take the bridge with me. It has great details and would be a shame to not make use of it.
|Run Away .. MATH!|
The Cross Girders and Rail Bearers of this casting are 1/4″ high. In HO that would represent an I-Beam 22″ high. In O scale of course, it would be 12″.
Just for fun. When you double the size of something .. H x W x L it cubes the volume. Looking at that another way .. if you had a steel cube measuring 1″ x 1″ x 1″ it would equal 1 cu. in. .. if you double the dimensions so you get .. 2″ x 2″ x 2″ the volume now is 8 cu. in. A narrow gauge locomotive is about 2/3 that of a standard gauge locomotive or 0.666~ …. therefore that same 1″ sq. cube reduced to .666″ x .666″ x .666″ would be 0.295 cu.in.
Round that to .3 .. so something 2/3 the size will weigh about 1/3. From the ‘American Civil Engineer’s handbook’ we have a chart. An I-Beam 21″ high weighing 100 lbs per foot has a Coefficient of strength of 1,766,100 (calculated load in pounds that will produce a stress of 16,000 lb per sq in on the extreme fiber when the span is 1 ft. By dividing this coefficient by the span in feet, the safe load uniformly distributed in pounds is found). Figuring 1/3 of that we get 588,111 COS. That equals to around a 15″ high beam at 40lbs per foot. a 12″ beam (that’s what the CV beams work out to in O scale) would have a COS of about 500,000. Since in “my world” the locomotives that will be using this bridge will be on the light side .. even for narrow gauge, that 12″ beam would probably be ok.
With that in mind I looked at what I have in my parts box as far as I-Beams. I have .. 3/16″, 5/16″ and 3/8″ Evergreen I-Beams. Cool. The 3/16″ I-Beam is too small as it would only be a 9″ I-Beam. The 3/8″ I-Beam would be a 18″ beam. The 5/16″ I-Beam would be a 15″ beam. Shazam! That will work! Now, the Evergreen 5/16″ I-Beam #278 has a flange width of .134″ which equals 6-1/2″. That is close to a 15″ I-Beam running 85 lbs per foot and having a COS of 1,131,000 which means it will more then be sufficient for our bridge. Cool.