The Case of the Falling Floor



The Case of the Falling Floor
The line was running when suddenly there was a loud thud. The floor, supporting a vertical beam had given way. What happened?
Mysteries of Science

Transcript


The Northern Engraving metal finishing plant had every kind of metal finishing and decorating process. There were 100 big presses for cutting, punching, and shaping metal. There were also many wet processes, including metal etching and cleaning.

One morning the etching line was running when suddenly, there was a loud thud and the entire building shook. One worker pointed to the ceiling, upon closer inspection it became clear that part of the ceiling had dropped by at least a foot. The ceiling was sagging, but still supported by its steel structure and I-beams.

The floor, supporting a main vertical I-beam, had given way. The plant was on very solid ground and the thick concrete floor rested on a well-settled gravel bed.

What caused the floor to give way in this particular area of the factory?

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Could the footing possibly have been bad? Maybe the concrete was bad? There was no obvious answer.

The ceiling was supported so that the area around the column could be excavated. As the digging proceeded, they exposed a black plastic pipe that ran under the floor. The layout plan showed that it was the waste acid pipe that went to the waste water treatment plant.

A joint was leaking into the surrounding concrete. The leak contained hydrofluoric acid used to etch glass and stone. The acid partially dissolved the floor and footing. The process may have taken quite awhile.

But ultimately the floor degraded enough to cause the problem.

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