Mansard Stability

The defining feature of a mansard roof, a sloped facade/roof, is mildly problematic as structure. Under just the gravity load of the wall’s own weight, there is a small overturning moment, which is resisted as an inward thrust at the top and an outward thrust at the base. If the sloped wall is carrying other …

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Why Did They Do That?

A large part of field investigation is trying to get inside the head of whoever designed and built the structure you are looking at.* The idea is that people do things for rational** reasons so if we can figure out those reasons we have a head-start on understanding the built result. The more you understand …

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Partly Hidden and Accidentally Photographed

I took the picture above just before the West Thames Street bridge was put in place. The mesh-enclosed tower in the middle is the elevator that will lead to the west side of the bridge, the gray-steel west pier of the bridge is just to its right. The center pier of the bridge, where the …

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Inadvertent Structural Action

The title of this post is recycled from a talk I gave 16 years ago, “Inadvertent Structural Action in Traditional Buildings; or Why Hasn’t That Fallen Down Yet?” That talk was about how buildings that were constructed without structural design are often stronger than we think they are. The picture above is not that, but …

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