If you are planning to build a large bridge, it is amazing just how much structural steel tubing/channel/angles/etc. are required. I once looked at building a large scale version of the Devil’s Gorge bridge in 1:32 - needed something like 1200’ of various profiles for the 12’ span! I decided I’d rather have a new car.
Anyway, there was a thread on the “other” large scale site last year about the structural strength of brass shapes when used for bridge construction. It inspired me to look into the possibility of forming my own shapes from galvanized sheet steel. I’m fortunate to have a fairly complete sheet metal shop and shearing/bending up to 16 gauge steel is not that difficult for me. Anyway, I made up some 48" long “C” channel from some scrap 20 gauge sheet lying around in my garage. The results were some channels that were 3/4" high with 1/4" deep flanges.
I then did some testing on them. Simply supported (placing the ends only on a couple of bricks) I used a dial indicator to measure deflection at the center of the span for a standardized weight. For this testing I used a single, center located weight of 10# - simulating the loading of a moving large scale train gets a bit more complicated, but could be approximated by developing a distributed load test - i.e., place a 2# weight every 6", etc.
Anyway, the results showed some fairly predictable patterns, but also showed promise for large scale bridge building. For those of you that care, I performed the testing on a Grade A 36 x 48" granite surface plate utilizing a Brown and Sharp dial indicator - suffice to say that this gives an accuracy far exceeding anything that would even be remotely required for LS bridge building. The results are the averages of three separate determinations - after set up, the weight would be gently laid/balanced at the center point, the result recorded, the weight removed and the process repeated. All the testing was done within a two hour period when the temperature was between 75-78^o F.
Placing a single channel flat (the two short legs facing down) resulted in a deflection of 0.486". Flipping the channel over improved the results - 0.425". This makes sense - the latter configuration exploits the compressive strength of the steel within the short legs.
Placing a single channel vertically was relatively simple, but balancing a 10# weight on the 1/4" wide flange was impossible, so I stacked some bricks to about 18" high and suspended the weight using some fishing line. Given the larger vertical cross section, the deflection was considerably less at 0.356".
Placing two channels vertically back to back to form an “H” column on its side resulted in a deflection of 0.226"
I then clamped the two channels together, drilled holes every 6" and pop riveted them together. As expected, deflection again decreased - now it was 0.208". I would suspect that tack welding would produce an even stiffer column.
At that point, I became convinced that it would be viable to build a bridge using home made structural shapes, though I had yet to fabricate angles, T’s or tubing sections.
I also have not tested any such shapes made from aluminum (you could get rolls of 0.032" aluminum that gutter installers use - could even get them precolored in a dark brown to represent rust). While aluminum would resist weather much better, welding it is much more problematic though possible. I suppose the structure could be designed to make pop rivets less visible if one objected to them.
Brian