aggiehawg said:
Here's a picture of the railway bridge while it was under construction. Maybe some of our resident engineers can comment on how redundant this structure is?
Also
I will use this pic to try and answer some of questions regarding steel melted in the recent vids.
The main structural beams are the two pairs of I beams assuming these carry through and are not just for launching during construction. This thing is a beast. On top of these is a deck that looks like a combination of box beams and stringer beams. The outside beams are ballast retainer beams to hold the gravel in. So there is several feet below top of rail to get to these main beams. This a 200+ foot span and bigger than anything we have done or even seen. I will say that at 150' those beams would be over 10' tall. There is a lot extra steel in this thing that i am not sure is for architectural or possibly corrosion resistance or both.
The beams shown melted are probably just ballast retainer and or the stringers in the deck. The ballast retainer would separate grades and or walkway from the rock.
Seeing the rail melted and the trucks is a good sign as those can be thicker than the web or flanges of the main beams. Even better at some point in the vid there is no ballast around a couple of ties. I suspect this is over the bent where an expansion joint is and the cover is simply a 1/2" plate whicb has melted allowing the ballast to fall through the joint, which means fuel could have also seeped though allowing fire to burn down where the critical steel is. This said we would rather have the steel weakens in the middle of the span where max deflection would occur on normal loading cycles. The ballast is typically 8-12" thick below the ties and 8-12" within the ties. Timber ties on BD bridge are 8" I cantt recall what concrete ties are which are on this bridge, we almost never see them.
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