Misleading Patterns

by Don Friedman on March 5, 2018

If we interpret the visible pattern literally, it looks like the leak that led to the rusting is worst at the bottom and least bad at the top. Thinking about it for a second leads to the almost-obvious conclusion that we can’t really tell about the top, because water will run or drip off the underside of the beam top flange. But then what?

Secondary influences can greatly change patterns of damage. The classic example is looking at burn patterns after a fire. It might look like the fire started and burned hottest at the back of a house when in reality the origin was at the front but so was the easiest access for fire-fighters. The secondary influence of geometry of access blurs the primary question of where the fire was actually located.

With secondary influences in mind, what do we see in the photo above? We can’t tell where the water was coming from because it was trapped by the thick ceiling (visible on the left) and therefore the most heavily rusted areas are there. Since water can move sideways in the space between the ceiling and the beams, we can’t even tell if the water was coming from the right, where the rust is worst.

There’s no real correlation between damage and the source of the damage. There is a correlation between the type of damage and the type of source: water rusts steel, differential settlement causes diagonal cracking, and rusting frames cause vertical and horizontal cracks.

Name That Material

February 7, 2018

That fuzzy thing that takes up most of the center of the photo? It’s one side of an old wet wall in this abandoned building. It’s a gypsum block partition, about halfway to reverting to being raw gypsum from its processed block state. Beautiful, in a morbid kind of way.

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Clickbait Headlines

January 19, 2018

The failure of the spillway at the Oroville Dam in California was a big story last year. The spillway failure had the potential to cause an overall failure of the dam, which would have been catastrophic. Emergency measures to lower the water behind the dam and repair the spillway worked, and a disaster was averted. […]

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Common Problems

January 18, 2018

The latest issue of the CROSS (Confidential Reporting on Structural-Safety) newsletter is out and I had a weird feeling of déjà vu while reading it. In the same order as within the newsletter, the topics include: Commentary on the rather grim UK government review of fire safety triggered by the horrific Grenfell Tower fire, Report […]

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Safety Is An Essentially Contested Concept

December 21, 2017

That’s a view of the wreckage of the excursion steamer General Slocum, run aground in the Bronx after burning in the East River. Over 1000 people died during that incident, so I think it’s safe to say the ship was not safe. I recently came across the definition of an essentially contested concept, and I think […]

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The Meaning of Failure

November 27, 2017

Trigger warning: The blog post below includes discussion of death in building failures. Definitions of structural engineering tend to be positive, as they should be. Safely and economically designing structures…that sort of thing. Engineers are, amazingly enough, human and prefer to think about success rather than failures. I’ve been working on a paper for the […]

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Relating Damage To Structural Type

November 22, 2017

Some stereoscopic views of Chicago after the 1871 fire: That’s the kind of devastation that a firestorm can cause. But it’s worth noting that different types of building fail differently. Nearly every building in Chicago before the fire was either of wood-stud construction (private houses and small commercial buildings) or of masonry walls with wood […]

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An Alarming Symptom, Maybe

October 23, 2017

Sometimes issues during an investigation aren’t clear. That picture is the entry to an abandoned church and that’s a really odd crack in the floor. I was there to do the most basic type of conditions assessment – hazard to the public or not? – and since the building was closed to use, the only […]

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Telegraphing Through

October 20, 2017

Another artistic photo, this time of one face of a party wall in a rowhouse. If you look closely (click on the picture to expand it), you’ll see that the plaster is well-adhered to the brick. The plaster didn’t fall off in that one area, it was removed. Why? Because the presence of that long, […]

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This Is Ungood

October 18, 2017

From a few years ago, some rotting wood beams and a failing brick pier. In 1989, I performed a long and difficult site visit to check on a structure I won’t name (confidentiality is still in place, even after all these years) that had to be reviewed once per year. The fellow who had been […]

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