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[QUOTE]Originally posted by George Harris: [QB] Train lady, I don't know quite how to deal with your long range worrying other than to quote, "Sufficient unto the day is the evil thereof" which realize really does not solve anything for you. Yes, it is a very slim chance, more like extremely slim. You must also understand that a lot of design and analysis effort deals with thing that approach the slim and none level of possibility. It must, because slim and none occassionally happens. Katrina was a good example of this. The engineers involved wanted stronger and higher levees because they knew that they were only good enough for the likely largest likely storm in 50 years. The politicians basically told them go away, you are being worry warts and scare mongers. Of course they were aslo thinking, "50 years. So what? I will be gone long before then." (A "50 year" storm means the likely largest in any given 50 year period, but it also means that you have a 2% chance every year of having one.) Katrina was something like the 200 year plus interval storm, and by the nature of its path hit New Orleans hardest at the weakest point. The New Orleans levee system started off and and is still primarily oriented toward protection against flooding from the Mississippi River with Lake Ponchartrain being the relief from the flood, not the source of the flood. We may never again have a storm hit the New Orleans and Gulf Coast as hard as Katrina did, or we may at sometime, anytime, over the next century have an even bigger one. No one really knows and those that talk like they do are talking nonsense. Back to your original question: As I said, yes, but highly unlikely. It was not a bridge, but the sort of thing that you describe is exactly what derailed the Texas Eagle near Marshall, Texas in 1983. Without going into a lot of details, the Texas Eagle was the third train to pass over what was a poorly done broken rail replacement. The new rail, not the old rail, shattered under the second or third car AFTER the TE's engines had passed over it. That is after carrying a few hundred axle loads of 20 to 32 plus tons, it shattered under an axle load of only about 15 tons. First and foremost lesson learned: The particular metallurgy of the new rail, a 1% chromium alloy, which was then being experimented with in the US, is no longer used, and so far as I know there is none left in track in the US. The improved hardness was gained at the cost of too much increase in brittleness. This is another of those things that supposedly worked great in Europe that some how rotted on the Atlantic crossing. It is no longer produced in Europe anymore, either. [/QB][/QUOTE]
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