This is 99% Invisible. I’m Roman Mars.
I want to be careful not to overstate what it means for a building to die. A building’s worth is an infinitesimal fraction of the worth of a person’s life. Even two buildings don’t even move the needle in comparison to real human loss. But a building is still a living thing in a way. It breathes. And it moves. This movement makes a sound. The structural engineer who designed the World Trade Center towers said that the people working inside couldn’t feel this movement of the towers swaying in the breeze. But they could hear it.
[Sound of the World Trade Center creaking]
Often buildings speak to you. What happens in a tall building is that, in the wind, as the building moves, the floor above moves with respect to the floor below. My full name is Leslie Robertson. I’m a structural engineer and I was responsible for the design of the World Trade Center. This cassette tape is one of many that we took during the construction and later occupation of the building. For each cycle of oscillation of the building, you hear two creaking noises. And therefore, if you have a tape of it, you can measure, rather precisely, the frequency of oscillation of the building itself. It takes ten seconds for the World Trade Center to go through a cycle of oscillation.
“This concludes the recording at the 67th-floor Tower A projection room.”
I don’t know much more I can say about it. I used to be an extremely sound sleeper. I’m the kind who would my head down on the pillow and go to sleep, and sleep for just a short while and get up and go back to work or do whatever. But it’s kind of not like that anymore. But I don’t have images of the Trade Center in my dreams. I do wake up with the thoughts in my head that I do, but it’s sort of like instantaneous and as you wipe your eyes, you wipe the thought out of your mind. People keep saying, “Well, you did everything you could have done. The design was the best it could be and, you know, all those thoughts. Which are nice but I guess ultimately the responsibility for… the criteria for, the Trade Center, that was mine, those were my decisions. And the fact that they stood up as long as they did was because we had designed the project for the impact of a 707 aircraft and we had a great team working on the project and they did what they were supposed to do. They stood up under the impact. And while it’s true that the plane that hit it was a bit heavier and it was flying a whole lot faster and therefore a whole lot more energy was put into the building, I think it’s a tribute to the people who worked on the project. That they did as well as they did and yet I know, as well as I’m here right this moment, that the buildings could have been made more solid, sure. They could have been made stronger and they could have stood up longer and that was my decision and that’s … I think in a sense I can’t be faulted because the structure’s performed in many ways admirably, but there’s always that nagging thought that maybe I should have done something else. And that I can’t… can’t just push that out of my head.
This episode of 99% Invisible was produced by the “Kitchen Sister,” Davia Nelson and Nikki Silva, and me, Roman Mars. It’s comprised of extracts and outtakes from the Peabody award-winning “Sonic Memorial Project” produced in 2002. A new 10-anniversary edition of the Sonic Memorial Project, which is narrated by my literary hero Paul Auster, is going to be playing on public radio stations around the country, is very much worth your time to seek out. You can find out more at kitchensisters.org.
This program, 99% Invisible, is made possible with support from LUNAR, making a difference with creativity. It’s a project of KALW 91.7, local public radio in San Francisco, the American Institute of Architects in San Francisco, and the Center for Architecture and Design. Find out more at 99percentinvisible.org.