Re: Box Girders and 6000 Flat Car Loading
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These are typical laced channel tower posts, also once widely used as bridge truss posts. Most of the weight is in the webs of the channels, which can vary considerably, within any one size. Channel size is measured across the web and over the flanges. Flange width is typically about 1/4 of the depth over flanges, and almost independent of weight.
From the 1932 Illinois Steel Shape Book, under structural channels, I find:
15" -- 6 weights, 33.9 to 55.0 lb/foot
12" -- 5 weights, 20.7 to 40.0 "
10" -- 6 weights, 15.3 to 35.0 "
9" -- 6 weights, 13.4 to 25.0 "
8" -- 5 weights, 11.5 to 21.3 "
7" -- 5 weights, 9.8 to 19.7 "
6" -- 4 weights, 8.2 to 15.5 "
I expect earlier shape listings to show a larger selection of sizes, and of weights within any one size, but these will give a good start.
Bridge post lacing sizes also vary considerably, but 1/4 by 3" is about the minimum cross section, and runs 2.518 lb/foot.
The size and weight used in any one application depended on design loading, post length, joint constraints, and the current cost and availability of specific sizes. The latter varied widely with the state of the steel market, enough occasionally to even dictate general design, so about all that can be said is that both size and weight generally increase with construction date and were driven by locomotive weights.
Let us know what you conclude.