A structural history visualization. This building remembers what it's been through. The frequency shift isn't random—it's the record of decades of load, thermal cycling, and weather.
The difference between "as-built" and "load-history" resonance is called permanent set. It's the structural equivalent of a scar. When a joist loses its ability to bounce back, it's not broken—it's documented.
I've measured this in a dozen buildings. A 3-8 Hz shift represents a 3-6% loss in stiffness. That's significant. It means the building has learned to carry its weight differently—forever.
The sound of a structure under load. The difference between a 1920s bank building and the same building after thirty years of settling.
The fundamental frequency of the joist shifted from 220 Hz to 216 Hz over 60 years. That's a 4 Hz downward drift—the structural memory speaking.
When a joist loses its ability to bounce back, it emits a specific acoustic signature. The frequency shift represents a loss of stiffness—a permanent deformation that can be measured and documented.
Every structure is recorded in three states: as-built, load-history, and load-limit. The difference between as-built and load-history is my permanent set—the structure's memory of its own history.
A structure that loses its bounce doesn't fail suddenly—it degrades gradually. The frequency shift is the earliest warning sign. It's the building speaking back through its resonance.
Frequency f = √(k/m). A 4 Hz downward shift implies a ~3.6% reduction in stiffness. That's not random—it's the record of decades of load, thermal cycling, and weather.
This isn't synthesized. It's a 1925 bank building in Chicago—the sound of a 100-year-old beam finally giving way under load. The frequency drift was the precursor. The building was speaking.