Misleading Intuition

by Don Friedman on March 30, 2017

In a recent conversation with an old friend who is simultaneously interested in and baffled by building engineering, I decided that the success of modern building technology has hidden itself. It’s ubiquitous, so no one thinks about it, so no one understands it.

The picture above is the old New York Times building under construction in 1903. (That’s the building with the ball drop on New Year’s Eve; the one that changed Longacre Square to Times Square.) It’s not just a modern steel-frame building, it’s showing off the new structural technology. The building is on a narrow triangular lot that couldn’t be used for a tall bearing-wall structure. More dramatically, the facade of the 6th through 9th floors is more or less complete while the facade of the 3rd through 5th floor has not been started. This is an example of the drama of constructing a masonry wall in mid-air, which depends on the use of skeleton framing.

In talking about an old building*, I mentioned in passing that it was a good example of an early steel-frame skyscraper. My friend asked where the steel was…was it behind the brick? The average non-engineer doesn’t really get the idea of how building structures work any more than I can point at my torso and say “here’s where my pancreas is.” It’s not a lack of intelligence, it’s the opaque nature of structures and the counterintuitive way in which we build. Bearing-wall buildings are intuitive: the things that look like they support the upper floors – the brick walls – do support the upper floors. When we say a building has a steel frame, people expect to see steel.

Skeleton-frame buildings are not intuitive in two different ways. Those that have masonry walls, like the Times Building, have prominent features that look structural but are not. The walls of older skeleton-frame buildings can be very thick: when I was working on some facade repair at the Whitehall Building about twenty years ago, I was shocked when I saw a six-wythe-thick (24 inches) brick parapet. But those thick walls are non-structural “curtain walls,” and a topic of conversation among designers and builders at the time of their construction was how thin they are. Those that have thin walls – glass curtain walls, for example – have little or no apparent vertical structure. They are physically transparent but logically opaque: what holds them up?

To those of us in the field, the structure is “visible” in that we understand the basics of the portions of the building we can’t see by inferring them from the portions we can. Certain types of exterior suggest steel frames and certain types suggest concrete. It is difficult for us to not see these things and so when we talk to the uninitiated we may gloss over concepts that they don’t know.

The solution to this problem, assuming that it is a problem and needs a solution, is for architects, engineers, and builders to use everyday language when speaking outside our circle and to gently explain what may seem obvious to us.

* The Bowling Green Offices at 11 Broadway.

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