Failure Portrait: Sometimes It’s Subtle

by Don Friedman on January 19, 2016

Not every failure is dangerous. Not every failure has a dramatic appearance. For example:

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This is a girder in a large one-story warehouse. Buildings like this are typically designed and built as efficiently as possible, meaning that the structure is as light as it can possibly be. The picture shows a shear-only connection between a cantilever end of a girder and a shorter girder span supported from the cantilever end. The splice plate was welded (probably during shop fabrication) to the cantilever end on the left and field bolted on the right. The bolt holes in the right-hand girder are slotted and therefore can allow some movement.

The paint tells the story: the girder on the right did not move for a long time and then abruptly shifted to a new position as the girder deflected down. Our investigation showed that a roof drain had become clogged and, during the thaw following a heavy snowstorm a few years ago, a very large pond built up in this area, near a drain. The water load exceeded the design snow load on the roof, and caused the girder to move. Our investigation was triggered by a foreman, present on the day the movement took place, saying it “sounded like a shot.” That was the sound of the paint breaking.

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