Synchronized rhythmic motion from ordinary dancers can resonate a huge building

Evidence

Some years back an older 40-story building in New York City abruptly began swaying from time to time, sometimes making occupants on the upper floors nauseous. Elevators stuck in their shafts. Norman Dotti of Russell Acoustics was called in to investigate. The cause turned out to be a new dance class held on an upper floor. About 30 people were stepping on and off stools in synchrony to music. That small periodic driving accumulated enough energy to noticeably sway a large office building to and fro! New flooring that reduced the coupling to the building was installed, but a much cheaper solution would have been to change the music to beat faster or slower! — Eric J. Heller, Why You Hear What You Hear- An…, 903

Categorization

• CANDY: 30 dancers on stools swaying a 40-story building is a perfect elevator-conversation fact.
• SHARE: Worth sending to an architectural or structural engineering friend — a concrete resonance failure case with a practical fix.
• ADDENDUM: Directly extends ‘On Sacrifice’… no — but relates to resonance infrastructure; actually supports the trees-as-infrastructure frame? It’s about structural resonance, loosely relevant to vibration physics of infrastructure.