I read the safety reports from CROSS with a kind of amused horror. As I recently said to another engineer, we all mistakes; the trick is to review our work so that we catch the mistakes before they get outside of our office. The CROSS reports describe mistakes that made it into the wild.
Report ID 1013, “Structural misunderstanding leads to historic church tower nearly being demolished” hits close to home. The short version is that people assumed there was a causal connection between some masonry damage on a tower and the carillon within. Examination showed that this was not possible in the way assumed because there was no dynamic load form the bells affecting the tower. It’s worth taking a look at the link to get the details.
I can’t even guess how many times I’ve heard someone give an explanation for structural damage – real or perceived – that was logical, concise, and wrong. It’s got to be more than a hundred buildings. In the case of the CROSS report, everyone knows that swinging bells damage church towers. I had a reviewer once criticize a gable roof design for a building extension because I did not have attic joists, saying that the thrust from the roof would destroy the building. I assumed that he had missed the fact that I had a ridge beam supporting the upper ends of the rafters, which eliminates the thrust, but in discussion found out I was wrong about that. He knew that gable roofs develop outward thrust and nothing, not the ridge beam on the drawings or a free-body diagram I drew for him, was going to convince him otherwise.
As Mark Twain said long ago: “It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”
The image is by Jacob Moore & contributors and is taken from The Mechanics Map.
