Time-frequency analysis of Transitory/Permanent frequency decrease in civil engineering structures during earthquakes

TL;DR

This paper employs advanced time-frequency analysis to monitor how resonance frequencies of civil structures change during earthquakes, revealing damage-related frequency drops in strong motions versus ground spectrum effects in weak ones.

Contribution

It introduces the use of the reassigned smoothed pseudo-Wigner-Ville method for precise frequency tracking during seismic events, distinguishing damage effects from ground motion influences.

Findings

Strong earthquakes cause quick frequency drops indicating structural damage.

Weak earthquakes show frequency variations due to ground motion spectrum, not damage.

Frequency increases slowly after initial drops in strong seismic events.

Abstract

The analysis of strong motion recordings in structures is crucial to understand the damaging process during earthquakes. A very precise time-frequency representation, the reassigned smoothed pseudo-Wigner-Ville method, allowed us to follow the variation of the Millikan Library (California) and the Grenoble City Hall building (France) resonance frequencies during earthquakes. Under strong motions, a quick frequency drop, attributed to damage of the soil-structure system, followed by a slower increase is found. However, in the case of weak earthquakes, we show that frequency variations come from the ground motion spectrum and cannot be interpreted in terms of change of the soil-structure system.