Re: iron or steel

Hi,

I think I recall that the conclusion was the original bridge was Wrought iron when they examined the burnt bridge.

The girders and cross bracing were replaced with steel. Only the bents were original on the burnt section.

Since iron and steel are stronger in compression, I suspect that the rebuilt section could support two of the K36 or K37 classes at once. Even if the entire deck was rebuilt with steel, I doubt I'd want to stress the original bents with a greater load. Fatigue failure (loading and unloading of a member not near its static failure point) would be a very big consideration.

The most notable bridge collapses (railroad or not) in recent years that I recall have been either due to an accident or fatigue failure. Until the past decade or two, most fatigue failures were undetectable because the cracks occurred internal to the metal. I believe that many forms are now detectable using ultrasonics and other methods.

If you know what a cold solder joint is, then you know what a fatigue failure is. For solder, you can just reheat and reflow the joint to allow the molecular structure to reform. For iron or steel, you basically have to remelt and reroll it at a steel mill.

Doug vV