| England has lots of Victorian railways bridges. Now, the Victorian engineers knew perfectly well how to build a railway bridge, which is why those bridges are still there. But they hadn't yet got to the place where you always properly document your work as you go, and they also didn't think too hard about (from their perspective) the distant future, our present. So a modern railway engineer inspecting a Victorian bridge has a problem. The bridge was built in the usual fashion of the time, and it's impractical to fully inspect the load-bearing materials without dismantling the bridge. There is no detailed paperwork because the Victorians didn't keep any. Still, it stands to reason that if the cast iron load structure exposed in one place has 15-20 years of life left in it, the unexposed structures you can't see are similar and this bridge can be scheduled for replacement in say 10-15 years. Right? And then, one night, as a fully laden freight train crosses it, the bridge collapses. The driver feels something wrong on the bridge and then, a few seconds later, the locomotive automatically brakes to a full halt - unable to sense the rear of the train which is in fact now laying in the rubble of the broken bridge. The Victorians saved a little money by using thinner metal for the unexposed girder, which had therefore failed earlier than the predictions based on the thicker metal. Documentation is essential. If your 30 year old C project doesn't have adequate documentation chances are you don't know whether those unexposed elements are as strong as the parts you can see or if they're paper thin and likely to fail at any moment. |